Electronic device with magnetization control functionality

Abstract

An electronic device is presented comprising: at least one basic block, and a control circuit. Each basic block comprises an active unit configured and operable to be responsive to one of circularly polarized electromagnetic field or circularly polarized spin current by a change in magnetization orientation in the active unit. The control circuit is configured and operable to carry out one of the following: (i) monitoring changes in at least one electrical property of the active unit to thereby monitor the change in magnetization orientation in the active unit in response to the circularly polarized electromagnetic field being applied to the active unit, or (ii) managing generation of the circularly polarized spin current in the active unit to thereby induce said change in the magnetization orientation in the active unit.

Description

ELECTRONIC DEVICE WITHMAGNETIZATION CONTROL FUNCTIONALITYTECHNOLOGICAL FIELDThe present disclosure is in the field of magnetization control techniques, and relates to magnetic devices, particularly magnetic sensors and magnetic memory units.BACKGROUND ARTReferences considered to be relevant as background to the presently disclosed subject matter are listed below:1. C.D. Stanciu, F. Hansteen, A.V. Kimel, A. Kirilyuk, A. Tsukamoto, A. Itoh, T. Rasing, All-Optical Magnetic Recording with Circularly Polarized Light, Physical Review Letters, 99 (2007) 047601.2. S. Mangin, M. Gottwald, C.H. Lambert, D. Steil, V. Uhlif, L. Pang, M. Hehn, S. Alebrand, M. Cinchetti, G. Malinowski, Y. Fainman, M. Aeschlimann, E.E. Fullerton, Engineered materials for all-optical helicity-dependent magnetic switching, Nature Materials, 13 (2014) 286-292.3. C.-H. Lambert, S. Mangin, B.S.D.C.S. Varaprasad, Y.K. Takahashi, M. Hehn, M. Cinchetti, G. Malinowski, K. Hono, Y. Fainman, M. Aeschlimann, E.E. Fullerton, All- optical control of ferromagnetic thin films and nanostructures, Science, 345 (2014) 1337- 1340.4. G. Kichin, M. Hehn, J. Gorchon, G. Malinowski, J. Hohlfeld, S. Mangin, From Multiple- to Single-Pulse All-Optical Helicity-Dependent Switching in Ferromagnetic Co / Pt Multilayers, Physical Review Applied, 12 (2019) 024019.5. G.-M. Choi, A. Schleife, D.G. Cahill, Optical-helicity-driven magnetization dynamics in metallic ferromagnets, Nature Communications, 8 (2017) 15085.6. G.P. Zhang, T. Latta, Z. Babyak, Y.H. Bai, T.F. George, All-optical spin switching: A new frontier in femtomagnetism — A short review and a simple theory, Modem Physics Letters B, 30 (2016) 16300052.7. R. Chimata, L. Isaeva, K. Kadas, A. Bergman, B. Sanyal, J.H. Mentink, M.I. Katsnelson, T. Rasing, A. Kirilyuk, A. Kimel, O. Eriksson, M. Pereiro, All-thermal switching of amorphous Gd-Fe alloys: Analysis of structural properties and magnetization dynamics, Physical Review B, 92 (2015) 094411.8. J. Gorchon, Y. Yang, J. Bokor, Model for multishot all-thermal all-optical switching in ferromagnets, Physical Review B, 94 (2016) 020409.9. Y. Quessab, M. Deb, J. Gorchon, M. Hehn, G. Malinowski, S. Mangin, Resolving the role of magnetic circular dichroism in multishot helicity-dependent all-optical switching, Physical Review B, 100 (2019) 024425.10. A. Capua, O. Kami, G. Eisenstein, A Finite-Difference Time-Domain Model for Quantum-Dot Lasers and Amplifiers in the Maxwell & Schrodinger Framework, IEEE Journal of Selected Topics in Quantum Electronics, 19 (2013) 1-10.11. A. Capua, O. Kami, G. Eisenstein, V. Sichkovskyi, V. Ivanov, J.P. Reithmaier, Coherent control in a semiconductor optical amplifier operating at room temperature, Nature Communications, 5 (2014) 5025.12. G. Klughertz, L. Friedland, P.-A. Hervieux, G. Manfredi, Spin-torque switching and control using chirped AC currents, Journal of Physics D: Applied Physics, 50 (2017) 415002.13. M. Brik, N. Bernstein, A. Capua, Coherent control in ferromagnets driven by microwave radiation and spin polarized current, Physical Review B, 102 (2020) 224308.14. B. Assouline, M. Brik, N. Bernstein, A. Capua, Amplification of electron- mediated spin currents by stimulated spin pumping, Physical Review Research, 4 (2022) L042014.15. A. Capua, C. Rettner, S.-H. Yang, T. Phung, S.S.P. Parkin, Ensemble-averaged Rabi oscillations in a ferromagnetic CoFeB film, Nature Commun., 8 (2017) 16004.16. A. Capua, S.-H. Yang, T. Phung, S.S.P. Parkin, Determination of intrinsic damping of perpendicularly magnetized ultrathin films from time-resolved precessional magnetization measurements, Physical Review B, 92 (2015) 224402.17. M. Caminale, A. Ghosh, S. Auffret, U. Ebels, K. Ollefs, F. Wilhelm, A. Rogalev, W.E. Bailey, Spin pumping damping and magnetic proximity effect in Pd and Pt spinsink layers, Physical Review B, 94 (2016) 014414.18. R. Mondal, M. Berritta, C. Paillard, S. Singh, B. Dkhil, P.M. Oppeneer, L. Bellaiche, Relativistic interaction Hamiltonian coupling the angular momentum of light and the electron spin, Physical Review B, 92 (2015) 100402.19. A. Capua, T. Wang, S.-H. Yang, C. Rettner, T. Phung, S.S.P. Parkin, Phase- resolved detection of the spin Hall angle by optical ferromagnetic resonance in perpendicularly magnetized thin films, Physical Review B, 95 (2017) 064401.20. T. Devolder, S. Couet, J. Swerts, G.S. Kar, Gilbert damping of high anisotropy Co / Pt multilayers, Journal of Physics D: Applied Physics, 51 (2018) 135002.21. C. Wang, Y. Liu, Ultrafast optical manipulation of magnetic order in ferromagnetic materials, Nano Convergence, 7 (2020) 35.22. H. Gomi, T. Yoshino, Resistivity, Seebeck coefficient, and thermal conductivity of platinum at high pressure and temperature, Physical Review B, 100 (2019) 214302.23. W. Lv, Y. Wang, W. Shi, W. Cheng, R. Huang, R. Zhong, Z. Zeng, Y. Fan, B. Zhang, Role of micro-nano fabrication process on the temperature coefficient of resistance of platinum thin films resistance temperature detector, Materials Letters, 309 (2022) 131313.24. G.-M. Choi, J.H. Oh, D.-K. Lee, S.-W. Lee, K.W. Kim, M. Lim, B.-C. Min, K.-J. Lee, H.-W. Lee, Optical spin-orbit torque in heavy metal -ferromagnet heterostructures, Nature Communications, 11 (2020) 1482.25. M.S. El Hadri, P. Pirro, C.H. Lambert, N. Bergeard, S. Petit-Watelot, M. Hehn, G. Malinowski, F. Montaigne, Y. Quessab, R. Medapalli, E.E. Fullerton, S. Mangin, Electrical characterization of all-optical helicity-dependent switching in ferromagnetic Hall crosses, Applied Physics Letters, 108 (2016) 092405.26. Elichai Frohlich, Chanan Naiman, Nirel Bernstein, Ranen Ben-Shalom, and Amir Capua “Localized excitation of magnetic fields using ultrashort optical pulses”, American Physics Society (APS), March meeting 2022 USA 2022.27. R. Medapalli, D. Afanasiev, D.K. Kim, Y. Quessab, S. Manna, S.A. Montoya, A. Kirilyuk, T. Rasing, A.V. Kimel, E.E. Fullerton, Multiscale dynamics of helicitydependent all-optical magnetization reversal in ferromagnetic Co / Pt multilayers, Physical Review B, 96 (2017) 224421.28. K.D. Stenning, X. Xiao, H.H. Holder, J.C. Gartside, A. Vanstone, O.W. Kennedy, R.F. Oulton, W.R. Branford, Low-power continuous-wave all-optical magnetic switching in ferromagnetic nanoarrays, Cell Reports Physical Science, 4 (2023).Acknowledgement of the above references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.BACKGROUNDThe ability to control and properly affect the magnetization of magnetic materials (i.e., the magnetic dipole moment per unit volume of the material) is fundamental to many applications, such as data storage, switching, etc. Generally, the techniques of affecting the magnetization of magnetic materials include: exposing the material to an external magnetic field; applying mechanical stress or strain; passing an electric current through the material.It is known from the literature [1] that an ultrafast laser pulse can be used to manipulate the spin degree of freedom allowing all-optical helicity-dependent spin switching (AOS), where a single ultrafast laser pulse can permanently switch the spin state in a magnetic material or compositions of magnetic materials without any assistance from a magnetic field. The experiments conducted based on this concept found dependencies on a variety of parameters including material composition, magnetic structure, and laser parameters, that were often experiment-specific.Magnetization affecting techniques are also used for implementation of logic nodes, i.e., use of magnetic elements to perform logic functions or store information. The introduction of non-volatility (NV) at cache level is a major challenge for advanced logic nodes as it would lead to a large decrease of the power consumption of microprocessors. Among NV memory technologies, Spin-Transfer-Torque (STT) magnetic random-access memory (MRAM) has gained a lot of attention due to its scalability, low power and relatively low access times, as well as a compatibility with scaled CMOS processes and voltages. Standard MRAM devices are magnetic tunnel junctions (MTJ). They consist of two ferromagnetic layers with perpendicular or in-plane magnetic anisotropy (PMA or IMA, respectively), separated by a thin oxide tunnel barrier, one of the layers being the storage layer (free layer) and the other used as reference layer (RL). Depending on the relative orientation of the magnetization of these two layers (parallel / anti-parallel), the MTJ cell exhibits low / high resistance, measured through the tunnel magneto-resistanceeffect (TMR), defining the reading state (0 / 1). The most common writing operation relies on STT, the transfer of spin angular momentum from the reference layer to the free layer.GENERAL DESCRIPTIONThere is a need in the art for a novel approach for affecting magnetization of materials, which can advantageously be used in variety of applications, while simplifying the device configuration and operation, and improving the device performance, e.g., by reducing the writing threshold of a Magnetic Random Access Memory (MRAM) device.The inventors have found that when using structures made of materials or material compositions possessing a spin orbit coupling (SOC), and properly configuring and operating such structures, control / altering of the magnetization can be improved. Moreover, such control / change of magnetization can be achieved in non-magnetic materials therefore simplifying the device configuration and its use in various applications.As described above, the all-optical helicity-dependent spin switching (AOS), where a single ultrafast circularly polarized laser pulse can permanently switch spin without any assistance from a magnetic field, has been proposed [1], The earliest demonstrations of the demagnetizing capability of intense optical pulses were carried out in metallic ferromagnets and explained by a phenomenological three-temperature model for phonons, photons and spins. Thereafter, the control of the magnetization using CP optical pulses was demonstrated in orthoferrites, and magnetization switching was demonstrated in ferrimagnets in the interaction known as the all-optical helicitydependent switching (AO-HDS) [1], Since then, the AO-HDS was discovered in a variety of materials, including ferromagnets [2, 3], and an extensive inquiry into the underlying mechanisms of the AO-HDS followed, resulting in the discovery of a multitude of mechanisms that entangle photons, spins, and phonons [9], These mechanisms encompass helicity-independent thermal effects that demagnetize the sample [7], photomagnetic effects induced by the absorption of photons such as magnetic circular dichroism, and non-ab sorptive optomagnetic effects that include the coherent stimulated Raman scattering and the inverse Faraday effect (IFE).Recently, the inventors have identified an additional mechanism for the transfer of angular momentum from the optical beam to spins of the material. Based on this mechanism, a helicity-dependent torque can be evaluated by introducing the opticalmagnetic field in the Landau-Lifshitz-Gilbert (LLG) equation, as will be described in detail further below. The findings revealed that the magnitude of the torque is proportional to the optical fluence and the spin-orbit coupling (SOC). In the LLG equation, the SOC of the material manifests through the Gilbert damping term (dissipation of energy when the magnetization of a magnetic material switches), which is prominent in heavy metals such as Pt. Interestingly, AO-HDS was reported in various studies which involve Pt layers [3, 5], strongly suggesting that beyond its primary function of inducing perpendicular magnetic anisotropy, Pt also plays a significant role in enhancing the optical torque.In the present disclosure, the inventors present novel configurations of electronic devices providing the generation of a helicity-dependent torque, further related to as “helical torque” (HT), in SOC-materials or material compositions, which may or may not be magnetic materials.In particular, heavy metals, such as Platinum (Pt), Gold (Au), as well as Bismuth (Bi), have strong spin-orbit coupling. Also, materials possessing SOC include transition metal oxides; some semiconductor materials (e.g., such as Indium Arsenide (InAs) and Gallium Arsenide (GaAs) exhibiting significant SOC due to their crystal structure and elemental properties; and Mercury Cadmium Telluride (HgCdTe) having strong SOC due to its heavy elements).Generally, the SOC-material or material composition suitable to be used in the technique of the present disclosure may be any electrically conductive material / material composition containing heavy atoms providing the desired SOC of said material / material composition. For example, Graphene, having typically weak SOC (due to its low atomic number carbon atoms), can be modified by incorporating heavy adatoms or creating bilayer graphene structures, to engineer the desirably SOC.The present disclosure, in some of its aspects, provides a novel approach for writing and / or reading data in a magnetic memory element by applying helical torque to the relevant layer of the memory element.Considering magnetic data storage techniques, as described above, the most common writing operation relies on STT, the transfer of spin angular momentum from the reference layer to the free layer. However, the shared read / write path of STT-MRAM devices can impair the read reliability, while the write current can impose a severe stress for the memory cell leading to a possible time dependent degradation of the MTJ. Tomitigate these issues, a next generation of STT-MRAM has been proposed, named Spin Orbit Torque MRAM (SOT-MRAM). SOT-MRAM uses a three terminal MTJ-based concept to isolate the read and the write path, significantly improving device endurance and read stability.Unlike STT-MRAM, magnetization reversal by spin-orbit torque (SOT) is performed using in-plane currents rather than passing the current through the tunneling barrier of the MTJ that has high resistance. Therefore, the magnetization reversal threshold in SOT-MRAM devices occurs in a low resistance mode. This lower threshold is one of the advantages of SOT-MRAM, as it potentially allows for faster switching speeds and lower power consumption. However, improvements are still required to allow adoption of this technology for commercial purposes.The technique of the present disclosure provides for generation of a helical torque resulting from circularly polarized spin current or circularly polarized electromagnetic field. Such helical torque provides higher torque on the magnetization reversal as compared to that achieved solely by the conventional DC current based approach used in SOT-MRAM technology.The results of the studies conducted by the inventors have shown the pivotal role of the spin-orbit coupling (SOC) in the transfer of angular momentum from the circularly polarized magnetic fields to spins in solids, in particular non-magnetic solids. For example, heavy metals such as Platinum and Palladium possessing high SOC can be used. The inventors demonstrated the relevance of this effect to the microwave regime, and provided DC field-free reversal schemes induced by circularly polarized (CP) microwave radiation and CP spin-orbit-torque (SOT), which are for example relevant for heavy metals, being a non-limiting example of SOC-materials (as described above). These schemes have broad ramifications for spintronics-based devices for magnetic memory applications, e.g., the magnetic tunneling junction (MTJ).The MTJ is a structure constituted from a free (floating) ferromagnetic (FM) layer, an insulator layer, and a fixed FM layer. The relative orientation of the magnetization of the two FM layers determines the resistance of the MTJ, where the magnetization of the free FM layer is switchable. Writing a bit is realized by passing a current through the MTJ. This is known as the STT-MRAM (spin transfer torque-MRAM), which is a commercially available technology. The next generation is the SOT-MRAM (spin orbit torque) and is generally based on spin currents that are generated for example but notlimited to the spin Hall effect. In the SOT-MRAM, writing occurs by introducing the Spin Hall effect metal layer underneath the free FM layer, where the current passing through the heavy metal generates a spin current and consequently exerts a magnetic torque on the free FM layer. However, the torque generated in the SOT-MRAM so far is not sufficiently strong for commercial purposes today.The present disclosure provides for using CP spin currents to exert the helical torque and switch the magnetization and / or using CP spin currents to reduce the switching current density threshold of a ferromagnetic layer, e.g., free layer in the MTJ-type magnetic memory unit. For example, a CP current (i.e., a charge current rotating in some plane clock- wise or counter-clockwise) is injected into the SOC-material layer and is converted into a CP spin current. The CP polarity and state of the spin current is controlled by a phase shifter. For a right (left) CP spin current, the resulting magnetic torque is upwards (downwards). Such a device can also be integrated in addition to conventional DC sources, such as DC magnetic field and / or DC spin current. In another example, CP RF radiation can be used, that can be generated by two micro-antennas, to irradiate the free layer of the memory element.More specifically, in some embodiments of the present disclosure, a magnetic memory element comprises: a ferromagnetic layer structure (e.g., free layer); and an electrically conductive non-magnetic unit located in a vicinity of the ferromagnetic layer structure, wherein the non-magnetic unit responds to alternating charge current passing therethrough by inducing a helical torque effect applied to the ferromagnetic layer structure. By this, magnetization reversal within the ferromagnetic layer structure is obtained, with significantly reduced magnetization reversal threshold.For example, the helical torque effect may be provided by configuring the nonmagnetic unit from two non-magnetic substrates and supplying thereto phase shifted (±7i / 2) alternating currents such that a circular spin-polarized current flows through the substrates and passes into the ferromagnetic layer structure interfacing with the nonmagnetic substrates. In another example, the helical torque effect may be provided by configuring the non-magnetic unit as antenna unit formed by a pair of antenna elements with the proper phase shift between the electric currents passing through the antenna elements, which results in that the non-magnetic unit responds to the alternating current passing therethrough by generation of circularly polarized RF field which irradiates theferromagnetic layer structure thereby applying the helical torque effect thereto causing magnetization reversal.In some other aspects, the present disclosure provides an electronic device which responds, by change in magnetization orientation, to interaction with externally applied circularly polarized electromagnetic field of an optical beam, or RF radiation or THz radiation or X-ray radiation. This allows for using the electronic device as sensor for radiation detection and evaluation of the radiation parameter(s). The sensor may include an MTJ-like structure (preferably with in-plane magnetization orientation of a free layer) or a Spin Valve structure, where an electrical property of the structure varying with the change of the magnetization orientation is resistance (i.e., tunneling magnetoresistance in case of the MTJ-like structure or Giant magnetoresistance in case of the Spin Valve structure). Thus, the resistance is measured to determine a change of tunneling magnetoresistance or giant magnetoresistance in response to the incident electromagnetic radiation (e.g., light beam), in order to extract the radiation parameter.In some other aspects of the present disclosure, it describes examples and theoretical support provided by the inventors of how the helical torque applied to SOC possessing structure (made of SOC-material or material composition as described above) can be used in optical applications, in particular in controlling / measuring intensity of optical field interacting with the SOC-structure.More specifically, the inventors have shown that when a circularly polarized optical field interacts with a SOC-structure, the magnetic field component of the circularly polarized optical field applies a helical torque to the SOC-structure causing local spin alignment in the interaction region of the SOC-structure, which is indicative of the intensity of the optical field in the interaction region.Thus, the inventors have shown that exposing a SOC-structure (i.e., a substrate, which is configured from a material composition possessing SOC) through which DC current flows, to interaction with CP light beam, provides for direct measure of the light beam intensity or a change in the light beam intensity. Based on such direct measure of light beam property from a local interaction of the light beam with the SOC-structure, a small and simple optical sensor can be provided, which can be integral with / embedded in an integrated structure of an electronic device.It should be noted that such a non-magnetic SOC-structure can be configured and operable as a Hall-element. This enables simple optical sensing by measuring the Hallvoltage variation caused by the Hall-element interaction with an optical field (incident light beam) to obtain data indicative of the optical field intensity.It should also be noted that such SOC-based optical sensors eliminate the need to provide specific crystalline structure of the sensor material, as needed with conventional optical sensors based on the detection of the electrical field of the optical radiation (for example, in semiconductor based detectors). The notion of the inventors that material composition possessing SOC is sufficient to implement the optical sensor, allows easy integration of the sensor e.g., during VLSI circuit design where the sensor can be placed directly on / in the chip. Further, if such SOC-structure is made of / contains magnetic material(s), a region / point of interaction with the CP light beam causes a local change of magnetization of the substrate, which can be used for example for data writing.Thus, according to one broad aspect of the present disclosure, there is provided an electronic device comprising: at least one basic block, each of said at least one basic block comprising an active unit configured and operable to be responsive to one of circularly polarized electromagnetic field or circularly polarized spin current by a change in magnetization orientation in the active unit; and a control circuit configured and operable to carry out one of the following: (i) monitoring changes in at least one electrical property of the active unit to thereby monitor the change in magnetization orientation in the active unit in response to the circularly polarized electromagnetic field being applied to the active unit, or (ii) managing generation of the circularly polarized spin current in the active unit to thereby induce said change in the magnetization orientation in the active unit.In some embodiments, each of said at least one basic block is configured for use with a magnetic memory unit. For example, each of said at least one basic block is configured for use with a magnetic unit of a magnetic tunnel junction (MTJ) type.In some embodiments, the basic block is configured as an integrated structure comprising: the active unit comprising a ferromagnetic layer configured with an initial magnetization, and a helical torque generator layer structure interfacing with said ferromagnetic layer, said helical torque generator layer structure being made of an electrically conductive material composition possessing spin orbit coupling (SOC). The control circuit is configured and operable to provide a phase shifted AC current supply to the helical torque generator layer structure thereby producing the circularly polarized spincurrent therein passing to said ferromagnetic layer interfacing with the torque generator layer structure resulting in a helical torque effect inducing the change of magnetization orientation by magnetization reversal in the ferromagnetic layer.In some embodiments, the basic block is configured as an integrated structure comprising: the active unit comprising a ferromagnetic layer configured with an initial magnetization to serve as a free layer of the magnetic memory unit, and a helical torque generator layer structure interfacing with said ferromagnetic layer, said helical torque generator layer structure being made of an electrically conductive material composition possessing spin orbit coupling (SOC). The control circuit is configured and operable to provide a phase shifted AC current supply to the helical torque generator layer structure thereby producing the circularly polarized spin current therein passing to the free layer interfacing with the torque generator layer structure resulting in a helical torque effect inducing the change of magnetization orientation by magnetization reversal in the free layer.In some embodiments, each of said at least one basic block is configured as a magnetic unit of a magnetic tunnel junction (MTJ) type. The basic block may comprise: an integrated structure comprising: the active unit comprising a first ferromagnetic layer configured with an initial magnetization and operable as a free layer, an insulator layer, and a second ferromagnetic layer having fixed magnetization; and a helical torque generator layer structure interfacing with said free layer, said helical torque generator layer structure being made of an electrically conductive material composition possessing spin orbit coupling. The control circuit is configured and operable to provide a phase shifted AC current supply to the helical torque generator layer structure thereby producing the circularly polarized spin current therein passing to the free layer interfacing with the torque generator layer structure resulting in a helical torque effect inducing the change of magnetization orientation by magnetization reversal in the free layer.The control circuit may be further configured to supply DC current to the helical torque generator layer structure.In some embodiments, the basic block comprises: the active unit comprising a ferromagnetic layer configured with an initial magnetization, and a helical torque generator comprising an antenna unit formed by a pair of antenna elements located in a vicinity of said ferromagnetic layer. The control circuit is configured and operable to provide a phase shifted AC current supply to the antenna elements producing generationof the circularly polarized electromagnetic field, being an RF field, by the antenna unit thereby applying a helical torque to said ferromagnetic layer inducing the change of magnetization orientation by magnetization reversal in the ferromagnetic layer.In some embodiments, the basic block comprises: the active unit comprising a first ferromagnetic layer having initial magnetization and being operable as a free layer, an insulator layer, and a second ferromagnetic layer having fixed magnetization; and a helical torque generator comprising an antenna unit formed by a pair of antenna elements located in a vicinity of said first ferromagnetic layer. The control circuit is configured and operable to provide a phase shifted AC current supply to the antenna elements producing generation of the circularly polarized electromagnetic field, being an RF field, by the antenna unit thereby applying a helical torque to said first ferromagnetic layer inducing the change of magnetization orientation by magnetization reversal in the first ferromagnetic layer.In some embodiments, the helical torque generator layer structure is made of at least one electrically conductive material composition comprising heavy atoms.In some embodiments, the helical torque generator layer structure is made of at least one electrically conductive material composition comprising one or more heavy metals.The helical torque generator layer structure may be made of the at least one electrically conductive non-magnetic material composition possessing spin orbit coupling.In some other embodiments, each of said at least one basic block is configured as a sensor for electromagnetic radiation being incident on / interacting with the active unit.In such sensor, the active unit may comprise an integrated structure configured as a magnetic tunnel junction (MTJ) structure comprising: a first layer, being either a ferromagnetic having an initial non-zero magnetization and operable as a free layer, an insulator layer, and a second ferromagnetic layer having fixed non-zero magnetization, the active unit being responsible to interaction with the circularly polarized electromagnetic field of an incident electromagnetic radiation beam by the change in the magnetization orientation in the free layer. The control circuit is configured and operable to provide electric current supply to the active unit and performing said monitoring of changes in resistance of the active unit caused by the change in the magnetization orientation in the free layer, and extracting data indicative of intensity of the incidentelectromagnetic radiation beam. The initial non-zero magnetization is preferably of inplane magnetization orientationIn another example of the electromagnetic radiation sensor configuration, the active unit comprises an integrated structure configured as a magnetic tunnel junction (MTJ) structure comprising: a first layer being a non-magnetic layer configured as a spin orbit coupling structure, an insulator layer, and a second ferromagnetic layer having fixed non-zero magnetization, the active unit being responsible to interaction with the circularly polarized electromagnetic field of an incident electromagnetic radiation beam by the change in the magnetization orientation in the first layer. The control circuit is configured and operable to provide electric current supply to the active unit and performing said monitoring of changes in resistance of the active unit caused by the change in the magnetization orientation in the first layer, and extracting data indicative of intensity of the incident electromagnetic radiation beam.In yet another example of the radiation sensor configuration, the active unit comprise an integrated structure configured as a Spin Valve structure comprising: a first ferromagnetic layer having an initial non-zero magnetization, an electrically-conductive layer, and a second ferromagnetic layer having fixed non-zero magnetization, the active unit being responsible to interaction with the circularly polarized electromagnetic field of an incident electromagnetic radiation beam by the change in the magnetization orientation in the first ferromagnetic layer. The control circuit is configured and operable to provide electric current supply to the active unit and performing said monitoring of changes in giant magnetoresistance of the active unit caused by the change in the magnetization orientation in the first layer, and extracting data indicative of intensity of the incident electromagnetic radiation beam. Similarly, the initial non-zero magnetization is preferably of in-plane magnetization orientation.In all the above examples of the sensor configuration, the active unit may further include a circular polarizer assembly accommodated at a side of said first layer intended for exposure to interaction with the incident electromagnetic radiation.In some other embodiments of the sensor configuration, the active unit comprises a Hall element made of one or more electrically conductive material compositions possessing spin orbit coupling. The control circuit is configured and operable to monitor the voltage changes in the active unit to thereby monitor the induced magnetization in the Hall element in response to the circularly polarized radiation being applied to the activeunit, and to extract data indicative of intensity of the circularly polarized radiation being incident on the Hall element from the voltage changes being measured. Similarly, the active unit may further comprise a circular polarizer assembly accommodated at a side of the Hall element intended for exposure to incident radiation.The Hall element may be made of the at least one electrically conductive nonmagnetic material composition possessing spin orbit coupling.It should be noted that in all the configurations of the basic block according to the present disclosure, the electronic device may comprise an integrated layer structure comprising: an array of spaced-apart individually operable basic blocks, each connected to the respective control circuit.BRIEF DESCRIPTION OF THE DRAWINGSIn order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:Fig- 1 is a block diagram of an electronic device based on the principles of the technique of the present disclosure;Fig. 2A illustrates, by way of a block diagram, a magnetic memory unit configured according to some embodiments of the present disclosure, where a helical torque generator is configured as SOC-structure supplying a circularly polarized spin current to the free layer of the memory unit;Figs. 2B to 2D more specifically illustrate three examples, respectively, of the implementation of the magnetic memory unit of Fig. 2A;Fig. 3A illustrates, by way of a block diagram, a magnetic memory unit configured according to some other embodiments of the present disclosure, where a helical torque generator is configured to apply a circularly polarized RF field to the free layer of the memory unit;Fig. 3B more specifically exemplifies the implementation of the magnetic memory unit of Fig. 3 A;Fig. 4A illustrates, by way of a block diagram, a sensor unit of yet further embodiments of the present disclosure, in which an active unit is configured to respondby induced magnetization to helical torque applied by magnetic field components of incident optical field;Fig. 4B exemplifies a sensing system utilizing the sensor device of Fig. 4A;Figs. 4C to 4F show exemplary embodiments of optical sensors based either on MTJ or on a spin valve configuration, wherein Figs. 4C and 4E show optical sensors based on MTJ configuration where the tunneling magnetoresistance of the MTJ is measured horizontally (Fig. 4C) or vertically (Fig. 4E) across the sensor layers following an incident CP light on the free layer; Figs. 4D and 4F show optical sensors based on spin valve configuration where the giant magnetoresistance is measured horizontally (Fig. 4D) or vertically (Fig. 4F) across the sensor layers following an incident CP light on the free layer;Fig. 5A illustrates schematically the analogy between the magnetization dynamics and the electrically pumped TLS, wherein left panel illustrates M on the Bloch sphere, and right panel illustrates the electrically pumped TLS; Fig. 5B illustrates the interaction withof Eq. (6), specifically, the temporal plots of Mz / Ms, Hpump yand normalized to unity are shown, corresponding toalternation between Hpumpiand Hpumpiis indicated by the shaded areasand occurs when \MZ\ reaches 0.99Ms; Fig. 5C illustrates interaction with Hpumpand a more realistic trailing edge, for the same conditions in Fig. 5B, full lines correspond to Hpumpl and dashed lines correspond to Hpumpy, The simulations in Figs. 5B and 5C are presented for Ms= 3 • 105A / m and Gilbert damping a = 0.025 (dissipation of energy when the magnetization of a magnetic material switches)

[0015] , and Hpumpiwas turned on at t = 0;Figs. 6A and 6B show the temporal evolution of the components of M under the influence of alternating Hpumpiand Hpumpi, wherein in Fig. 6A a = 0.025 and in Fig. 6B a = 0.25; an RCP (LCP) component in the trajectory of M is acquired for the application o Insets illustrate the trajectory of M along the Blochsphere; Black dashed lines indicate the alternation between Hpumpiand Hpumpy, In Fig. 6Bpto preserve while the large a was chosen forvisualization purpose;Fig. 7A shows magnetization reversal induced by an RCP Gaussian pulse for a = 0.035, Ms= 3 • 105A / m, η = 2.5 • 10-4and tpeak= 10 psec, top and middle panels depict the temporal evolution of the x and y components of M and Hoptin normalized units, bottom panel depicts Mz / Ms,.Fig. 7B shows Mz / Ms, for the application of an LCP pulse;Fig. 7C shows magnetization reversal induced by an RCP Gaussian pulse for η = 1 and tpeak= 50 fsec, Top panel presents the temporal behavior of | Hopt| and rα, where H Second and third panels depict the temporalevolution of the x and y components of M and Hoptin normalized units; Bottom panel depicts Mz / Ms(black solid lines represent the analytical solution of r / Ms. Insets: trajectory along the Bloch sphere for t > 55 fsecyFig. 7D shows Mz / Ms, for the application of an LCP pulse (black solid lines represent the analytical solution of r / Ms. Insets: trajectory along the Bloch sphere for t > 55 fsec),Fig- 8 shows magnetization dynamics induced by a 0.3 T RCP pulse, for a = 0.025, Tp= 675 fs, results are normalized by Ms;Figs. 9A and 9B show the effects of inclusion of Hanis(anisotropy field), specifically, the temporal trace of the magnetization simulated for the same conditions as in Fig. 7A, without the inclusion of anisotropy (Fig. 9A) and with the inclusion of anisotropy (Fig. 9B), respectively; M was initialized in the x direction;Fig. 10 shows numerical calculation of the amplitude of the Gaussian envelope of Hopt(t) when |Mz(t) | decreases to 0.5Msduring the reversal. where m800nmcorresponds to an opticalwavelength of 800nm and a = 0.025; The different curves correspond to applied pulses with three different wavelengths A G {533nm, 640nm, 800nm} and two different pulse durations The three solid thin lines correspond tofor the three different wavelengths and reproduce thecalculated curves well; Hx / 2isseento be independent from Tp;Fig. 11 shows 6 panels of temporal evolution, wherein: first, second, and third panels depict, respectively, the temporal evolution of the normalized Mxand Hpiase x,Myand Hpiase y, and Mz; fourth, fifth, and sixth panels depict the temporal evolution of the not-normalized primary torque, damping torque, z component of the total torque, respectively; the insets show: z component of the primary (total) torque for t = 60 — 75 fsec where the reversal of Mzoccurs, p = 1, a = 0.035, Tp= 10 fsec,Fig. 12 shows magnetization switching induced by RCP and LCP pulses, for a = 0.025, Tp= 10 fsec, for a 1pm wavelength;Fig. 13 shows magnetization switching induced by RCP and LCP pulses, for a = 0.0075, Tp = 10 fsec, for a 1pm wavelength;Fig. 14 shows magnetization switching cannot be induced by RCP and LCP pulses when a = 10-4, Tp= 10 fsec, for a 1pm wavelength;Fig. 15 shows magnetization switching induced by RCP and LCP pulses, for a = 0.025, Tp = 10 psec, for a 1mm wavelength;Figs. 16A to 16C show temporal trace of Mz / Mssimulated for the same conditions as in Fig. 7A, for Hpeak= 7.3 • 107zl / m and a = 0.025 (Fig. 16A), a = 0.035 (Fig. 16B), and a = 0.06 (Fig. 16C);Fig. 17A shows temporal evolution of M induced by a CW RCP microwave magnetic field under p = 1.5 x 10-2; Top and middle panels depict the evolution of the x and y components of M and HRF cwin normalized units, and bottom panel depicts Mz / Ms, M is initialized in the x direction; Fig. 17B shows temporal evolution of Mz / Ms, M is initialized in the z direction; Fig. 17C shows temporal evolution of M induced by a CW LCP STT excitation under Jc ac~ 2.5 x 1010[A / m2] ; Top and middle panels depict the evolution of the x and y components of M and SRF cwin normalized units, and bottom panel depicts Mz / Ms. M is initialized in the x direction; and Fig. 17D shows temporal evolution of Mz / Ms, M is initialized in the z direction, a = 0.025;Fig. 18 shows 8 panels of temporal evolution of M under pulsed microwave radiation \ STT excitations, for different polarization states, wherein first, second, and third panel in each plot in the right (left) column depicts, respectively, the temporal evolution of the normalized Mxand SRF x(HRF x), Myand SRF y(HRF y), and Mz, where SRF(HRF) is a 1 GHz STT (radiation) excitation; M starts aligned in the x direction, and a = 0.025;Fig. 19 shows 8 panels of temporal evolution of M driven by RCP \ LCP CW STT excitations in the absence of an external static field, wherein first, second, and third panel in each plot depicts, respectively, the temporal evolution of the normalized Mxand SRFcwx, My and SRF CWy, and Mz, where SRF cwis a 1 GHz CP STT excitation induced by an ac charge current of amplitude Jc ac, Left column: SRF cwis RCP, M starts aligned in the x direction, and a = 0.025; Right column: SRF CWis LCP, M starts aligned in the x + y + z direction, and a = 0. 05; andFig. 20 shows 8 panels of temporal evolution of M driven by RCP \ LCP CW STT excitations in the absence of an external static field, wherein first, second, and third panel in each plot depicts, respectively, the temporal evolution of the normalized Mxand SRFcwx, My and SRF Cwy, and Mz, where SRF CWis a 2 GHz CP STT excitation induced by an ac charge current of amplitude Jc ac, Left column: SRF cwis LCP, M starts aligned in the x direction, and a = 0.05; Right column: SRF CWis RCP, M starts aligned in the x + y — z direction, and a = 0. 025.Fig. 21A schematically illustrates the longitudinal and transverse torques induced by the optical pulse., Fig. 21B shows the transverse torque |TZ| after the application of an RCP Gaussian magnetic pulse as a function of p = ay'Hpeak / fopt, zp= 540 fsec,- the different curves correspond to a = 0.025, 0.05 and A = 800, 640 nm; dashed lines correspond to quadratic fits; Fig. 21C shows the dependence of |TZ| on zp, under p = 2 x 10-4; dashed lines correspond to linear fits; Fig. 21D shows Tzas a function of Φ, under p = 2 x 10-4and Tp= 540 fsec,- dashed lines correspond to — fits; Figs. 21C and 21D follow the color code of Fig. 21B;Fig. 22A shows temporal evolution of m = M / Msinduced by an RCP Gaussian pulse under p = 2 x 10-4and Tp= 540 fsec, tpeak= 2 psec, top and middle panels depict the temporal evolution of the x and y components of m and Hoptin normalized units, and the bottom panel depicts mz(t); Fig. 22B shows temporal evolution of m under i] = 2 x 10-4and zp= 54 fsec, induced by 10 RCP Gaussian magnetic pulses; for visibility, green dashed lines representing Tzinduced by each pulse were added; Fig. 22C shows | Tz| after the application of RCP pulses as a function of p and the number of pulses, where zp= 54 fsec for each pulse; yellow and green curves correspond to quadratic andlinear fits, respectively, and are guides to the eye; a = 0.025 and A = 800 nm in Figs. 22A to 22C;Fig. 23 shows temporal evolution of m induced by a CW RCP magnetic field under g = 10-7; top and middle panels depict the evolution of the x and y components of m and Hopt cwin normalized units, and bottom panel depicts mz; m is initialized in the x direction;Figs. 24A and 24B show log10(]Tz|) after the application of an RCP optical magnetic pulse of duration Tpand amplitude r / Hth. a = 0.025,2. = 800 nm; M is initialized in the x direction, wherein Fig. 24A shows numerical integration of the LLG equation, and Fig. 24B shows fitted matrix generated according to heatmapsare presented on a logarithmic scale for visibility; andFig. 25 shows log10( | Tz|) after the application of an RCP optical magnetic pulse of duration Tpand amplitude g; the different panels correspond to simulated values of a = 0.05, 0.025, 0.0125 and A = 800, 640 nm; M is initialized in the x direction; Hthis scaled according to the relevant a and foptin each panel; Tpis given in units of the optical cycle time.DETAILED DESCRIPTION OF EMBODIMENTSAs described above, the present disclosure provides a novel approach for affecting magnetization of materials, i.e., inducing magnetization in the material or inducing magnetization reversal of the material.Reference is made to Fig. 1 illustrating, by way of a block diagram, an electronic device 10 configured and operable according to the technique of the present disclosure. The device 10 includes an active unit 30 which is configured to respond to an effect of helical torque produced by a helical torque generator 14 by induced magnetization or by induced change in magnetization orientation (e.g., magnetization reversal). The electronic device 10 is associated with a control circuit 16, which is configured to manage operation of the active unit 30 and / or the helical torque generator 14 as will be exemplified further below.The electronic device 10 (or at least the active unit 30) may be configured as a basic block or unit cell of a magnetic assembly formed by an array / matrix of such individually operable unit cells.In some embodiments, the active unit 30 presents the basic block or unit cell and is configured as a magnetic unit cell (such as used in magnetic memory applications), where the application of the helical torque (produced by the helical torque generator 14) enables to read and / or write data in a free layer, constituting the active unit 12, of the magnetic unit cell 10.Fig. 2A schematically illustrates a magnetic unit cell 100 configured according to some embodiments of the magnetic unit cell of the present disclosure. To facilitate understanding, functionally similar elements in all the examples described herein are designated by the same reference numbers. The magnetic unit cell 100 includes helical torque generator 14 which is configured to produce the helical torque effect in the form of a circularly polarized (CP) spin current, which is supplied to the active unit 30 (which may be constituted by the ferromagnetic layer 12) to induce a change in magnetization orientation resulting in magnetization reversal in the ferromagnetic layer 12. In this case, the active unit 12 / 30 and the helical torque generator 14 are implemented as integrated structure with direct interface between the helical torque generator and active unit layers.The helical torque generator 14 is configured as an electrically conductive structure that can generate spin currents, for example by the spin Hall effect (SHE). If the SHE is used, the helical torque generator 14 is preferably configured as spin orbit coupling (SOC) structure, i.e., is made of electrically conductive material(s) or material composition(s), which may or may not be magnetic, possessing relatively strong spin orbit coupling. The spin orbit coupling results in a sizable SHE, for example having a spin Hall angle of more than 0.01 (unit less number). It should be noted that additional ways can be implemented to generate spin currents besides the SHE, for example by the orbital Hall effect, Rashba-Edel stein effect and similar.As described above, a SOC-structure suitable to be used in the electronic device of the present disclosure may be made of any electrically conductive material(s) / material composition(s) containing (e.g., engineered to contain) heavy atoms providing the desired SOC of said material(s) / material composition(s). In particular, heavy metals, such as Platinum (Pt), Gold (Au), Tungsten (W), Tantalum (Ta), as well as Bismuth (Bi), having strong spin-orbit coupling can be used.As also shown in Fig. 2A, the control circuit 16 includes an AC current supply unit 18 configured and operable to supply a phase-shifted AC current to the helical torquegenerator 14. As also shown in the figure, the control circuit 16 may also include a DC voltage supply unit 20.Figs. 2B to 2D illustrate specific but not limiting examples of the implementation of the magnetic memory unit cell 100 of Fig. 2A. In the non-limiting examples of Figs. 2B-2D, the unit cell 100 is configured for use with a typical MTJ structure (which may constitute the active unit 30) of the SOT-MRAM technology. It should, however, be noted that for the purposes of the technique of the present disclosure the active unit may be constituted by a ferromagnetic layer structure, which is not necessarily a part of the MTJ structure. It should also be noted that in these non-limiting examples, the MTJ structure is exemplified as having perpendicular magnetization; however, such structure can work also with in-plane magnetization.The MTJ structure 30 is formed by a free ferromagnetic layer FL (12), an insulator layer IL, and a fixed (pinned) ferromagnetic layer PL, wherein, for the purposes of the present disclosure, the free ferromagnetic layer FL constitutes the active unit 30 interfacing with (e.g., located on top of) a layer structure of the helical torque generator 14. According to the present disclosure, the helical torque generator layer structure 14 is configured and operable to generate CP spin current therein which flows into the free layer 12 enabling magnetization reversal thereof.In the example of Fig. 2B, the generation of the CP spin current in the layer structure 14 is achieved by configuring the SOC layer structure 14 as an SHE metal structure (i.e., structure exhibiting a significant Spin Hall Effect (SHE) due to its intrinsic spin-orbit coupling and conductivity properties), wherein such SHE metal structure is supplied with phase shifted (±K / 2) AC current, resulting in the creation of the CP spin current (instead of conventionally used spin current resulting in DC torque). To this end, as shown in the figure, the control circuit includes the AC current supply unit 18 including an AC signal generator and a phase shifter. As noted above, the SHE metal(s) composition of the layer structure 14 may be heavy metals containing composition.In the example of Fig. 2C, the magnetic memory unit cell 100 is configured generally similar to that of Fig. 2B, i.e., the layer structure 14 is configured as an SHE metal structure. Here, however, the SHE metal structure is connected to the conventional DC voltage supply 20 typically used to operate SOT-based memory unit cells and additionally supplied with the phase shifted (±K / 2) AC current from the properly configured AC current supply 18. This results in the generation of the CP spin current, inaddition to a conventionally used spin current (i.e., DC torque) in the layer structure 14 and transfer of the CP spin current to the free layer 12, thereby applying higher force torque resulting in magnetization reversal with a reduced threshold thereof.Fig. 2D more specifically exemplifies the magnetic memory unit cell 100 configured according to the present disclosure for attaching / coupling (e.g., via material deposition) to the other layer structure 35 to complete the MTJ resulting in a novel magnetic memory device 300 of the present disclosure. In this specific non-limiting example, the SOC structure of the helical torque generator 14 is shown as being made of heavy metals. However, it should be understood that the principles of the present disclosure are not limited to this specific example of the implementation of the SOC structure. As shown, the SOC-structure is supplied with the phase-shifted AC current to thereby create the CP spin polarized current in the structure 14 propagating to the free layer 12, to thereby enable magnetization reversal effect.The configuration and operation of the MTJ structure are known per se and do not form part of the present disclosure and therefore need not be specifically described. However, it should be understood that the novel magnetic memory device 300, in which the free layer of the MTJ structure interfaces with the helical torque generator 14 in the form of SHE structure in which CP spin current can flow (due to the phase shifted AC current supply), provides for data writing in the MTJ structure with significantly reduced magnetization reversal threshold and, in some embodiments, may make the conventional DC current completely redundant.Reference is made to Figs. 3A and 3B exemplifying some other embodiments of using the technique of the present disclosure in magnetic memory technology. Here, the helical torque effect is in the form of a CP RF field which when applied to the free layer of the magnetic memory structure induces magnetization reversal thereof.Fig. 3A illustrates, by way of block diagram, a magnetic memory unit 200 including an active unit 30 constituted by the free layer of e.g., MTJ structure, and a helical torque generator 14 located in the vicinity of the active unit 30 and configured for generating RF field. The magnetic memory unit 200 is associated with a control circuit 16 which includes an AC current supply unit 18 configured for supplying phase-shifted AC current to the RF field generator, inducing circular polarization of the RF field. Exposure of the free layer 12 to such CP RF field results in the creation of the CP currents in the free layer 12 inducing magnetization reversal thereof.As shown in Fig. 3B, the RF field generator 14 is an antenna unit formed by a pair of two micro-antenna elements 14A and 14B, through which electric currents flow with a phase shift between them. This results in circularly polarized RF field generated by the antenna 14.Reference is now made to Figs. 4A to 4F exemplifying how the principles of the present disclosure can be used in electromagnetic radiation sensing technology. The technique of the present disclosure provides for monitoring properties of electromagnetic radiation (typically, radiation intensity) via measurements of changes in electrical property of an active unit 30 in response to an effect of the magnetic field component of a circularly polarized radiation beam interacting with the active unit.In some embodiments of the radiation sensing configuration, the active unit is configured as a magnetic unit, e.g., magnetic unit having configuration generally similar to that of MTJ structure or Spin Valve structure. In these embodiments, the electrical property being changed in response to interaction with the circularly polarized incident radiation may be induced magnetization or a change in magnetization orientation.In some other embodiments of the radiation sensing configuration, the active unit may include a Hall substrate made of SOC material(s). In this case, the electrical property being changed in response to interaction with the circularly polarized electromagnetic radiation is induced magnetization in the SOC Hall substrate that can be measured via a voltage change.Generally, such external electromagnetic radiation may be optical, THz or X-ray radiation. More specifically the technique of this aspect of the present disclosure is used for measuring properties of a light beam and is therefore exemplified here with respect to this application.As shown schematically in Fig. 4A, the electronic device 400 of the present disclosure includes an active unit 30 which in this non-limiting example is illustrated as an MTJ-type structure or a Spin Valve structure (SVS). Such active unit 30 includes a layer 12 exposed to the interaction with the light beam. This layer may be a ferromagnetic layer (free layer) having initial non-zero magnetization (which is preferably in-plane magnetization), or a non-magnetic SOC-structure (e.g., heavy metal containing structure). Exposing this layer 12 to circularly polarized electromagnetic field of the circularly polarized light beam results in a change in the magnetization orientation in the ferromagnetic layer 12, or induces magnetization of the non-magnetic SOC structure(change from zero magnetization) being maintained while interacting with the light beam. Such change in the magnetization orientation of the layer causes a change in the resistance of the MTJ / SVS that can be measured, and used to extract the light beam intensity.More specifically, the active unit 30 is configured to respond, by either one of induced magnetization, a change in magnetization orientation, or magnetization reversal, to the magnetic field component of incident / interacting circularly polarized optical field. The change in the magnetization of the layer 12 is sensed by measuring the resistance of the active unit 30.Thus, in the optical sensor embodiments, the element 12 of the active unit 30 is exposed to a helical torque effect induced by a circularly polarized magnetic field being the magnetic field component of a circularly polarized light beam 414 which operates as the helical torque generator. To this end, a circular polarizer 15 is provided at the light interfacing side of the element 12 of the active unit. The circular polarizer includes a quarter-wave plate 15A, and possibly also a linear polarizer 15B located upstream of the quarter-wave plate 15A (with respect to the incident light propagation direction towards the element).As also shown in the figure, the electronic device 400 may optionally include a lens unit 17 (one or more lenses) to enable properly focus the incident light beam onto the element 12 of the active unit and by this concentrate the optical field fluence on the active unit.The electronic device 400 is associated with a control circuit 16, which includes an electrical current supply unit 18A, and resistance measurement circuit 18B, and also includes a light intensity extractor circuit 22 which extracts data indicative of the light intensity of the interacting circularly polarized light beam from the measured change in resistance. Such data indicative of the light intensity may include the intensity value or a change of the intensity.As exemplified in Fig. 4B, the present invention provides an imaging system 500 including a layer structure including a layer 112 formed by an array / matrix of AT spaced apart individually operable active units 30 (e.g., magnetic memory units as described above, or SOC Hall-substrates), a circular polarizer layer 15 in the vicinity of the active units' layer, forming together a pixel arrangement. Also preferably provided is a microlens layer 117 formed by an array of K (K<M) spaced-apart micro-lenses 17. A readout circuit 116 (which may be incorporated in a substrate layer carrying the active units' layer)includes M individual control circuits 16 associated with the M active units, respectively, each managing the electrical current supply to the respective active unit, measurement of the resistance change (or Hall voltage changes) and extraction of data indicative of light intensity of a light beam being incident on / interacting with the respective active unit (layer 12).Figs. 4C to 4F show exemplary embodiments of optical sensors utilizing either MTJ-type configuration or a Spin Valve configuration. Figs. 4C and 4E show optical sensors 700 and 720 utilizing the MTJ configuration where the ferromagnetic layer, being a free layer having certain initial non-zero magnetization, is spaced by an insulator layer from a ferromagnetic layer, being a pinned layer PL having a certain fixed non-zero magnetization. Figs. 4D and 4F show optical sensors 710 and 730 utilizing the SVS configuration where the ferromagnetic layer being a free layer is spaced from a ferromagnetic layer being a pinned layer PL by a non-magnetic electrically conductive layer.It should be noted that the optical sensor may function also when the ferromagnetic free layer in the Spin Valve structure is replaced with a non-magnetic SOC layer, e.g. made of heavy metal.While the magnetization in the pinned layer PL is fixed, the orientation of magnetization of the free layer FL is determined by the torque acting on the magnetization in the free layer. For a small perturbation, the relative orientation is linear with the torque. At large perturbation the sinusoidal of the relative orientation equals the torque: 5m(0) oc Torque (Tz).Referring to Figs. 4C and 4E, the operation of sensors 700 and 720 is based on measuring the resistance (i.e., tunneling magnetoresistance) of the MTJ while passing current therethrough horizontally (sensor 700 in 4C) or vertically (sensor 720 in Fig. 4E) enabling to detect and measure the resistance change caused by incidence of CP light on the free layer FL. The circular torque induced by the incident CP light affects the initial magnetization orientation M of free layer and thus affects a relative magnetization alignment in the free layer FL with respect to that of the pinned layer PL causing a change in the resistance of the sensor (MTJ structure). The measured resistance of the sensor relies on the tunneling magnetoresistance (TMR), where electrons tunnel through the insulator, with resistance depending on the relative magnetization alignment. As will beshown further below, the measured resistance is quantitatively related to the applied light intensity.In the sensor configuration based on spin valve structure giant magnetoresistance (GMR) is measured. Figs. 4D and 4F show optical sensors 710 and 730 based on a spin valve configuration. A spin valve is a device used in spintronics that exploits the electron's spin and charge. Each of the sensors 710 and 730 includes two ferromagnetic layers, PL (pinned layer) and FL (free layer) separated by a non-magnetic electrically-conductive (metallic) layer. The electrical resistance of the spin valve depends on the relative alignment of the magnetizations of the ferromagnetic layers: it is low when the magnetizations are parallel and high when they are antiparallel. This change in resistance, known as giant magnetoresistance (GMR), is utilized in applications such as magnetic field sensors and data storage.It is noted that in general, MTJs typically offer higher sensitivity and larger resistance changes compared to spin valves, making them more efficient for certain applications like MRAM. The differences between MTJs and spin valves (e.g., structural differences) result in distinct operational mechanisms and applications for spin valves and MTJs in the field of spintronics. However, in both configurations (MTJ and spin valve) the measured resistance of the device is determined from the relative orientation (angle) between the pinned layer (PL) and the free layer (FL).Various initial relative orientations can be used: the magnetization of the pinned layer PL can be either fixed in-plane or out-of-plane. For the purposes of the optical sensing of the present disclosure, the magnetization of the free layer FL is initialized inplane, such that the longitudinal torque induced by the CP optical field excitation would change its longitudinal component and hence its relative orientation as compared to the pinned layer PL, resulting in a continuous change of resistance irrespective of whether the magnetization reversal is reached or not.It should be noted that an all-optical helicity dependent switching (AO-HDS) effect resulting from interaction of optical pulses with magnetic materials is generally known. The inventors have previously shown

[0026] that ultrafast optical pulses are capable of inducing spin reversal resulting in localized magnetic fields even in non-magnetic metals, and demonstrated the results in an electrical Hall measurement on Pt and Ta layers, in the absence of an external magnetic field. A correlation between the Hall sign of the paramagnets Pt and Ta and their optical Hall helicity-dependent response has beenfound. The signal being measured during the influence of an incident beam was analyzed, and it was shown that it can be regarded as comprised of both an effective magnetic field and thermal components, which lead to the identified signal asymmetry.In the present disclosure, the inventors present theoretical understanding of the inventors of their previously conducted measurements resulting in further improvement of the system configuration and practical applications based on this theory, such as optical sensors and magnetic memory devices. More specifically, the inventors have shown the advantageous use of the non-magnetic electrically conductive material(s) or material composition(s), provided they possess sufficient SOC that translates to Gilbert damping of more than 0.0001 (it can work with even lower values). It is also important to note that the technique of the present disclosure advantageously eliminates a need for crystalline structure of such non-magnetic SOC materials, which is particularly important for optical sensors because this enables easy incorporation / integration of the optical sensors of the present disclosure in integrated circuit structures, i.e., technology with many devices on one chip. Further, it should be noted that the technique of the present disclosure provides for using electromagnetic radiation pulses to induce spin reversal resulting in localized magnetic fields even in non-magnetic metals.Ferromagnetic resonance (FMR) experiments are usually carried out at the GHz range. In contrast, optical fields oscillate much faster, at ~ 400 — 800 THz. Therefore, it seems unlikely that such fast-oscillating fields may interact with magnetic moments. However, the amplitude of the magnetic field in ultrashort optical pulses can, temporarily, be very large such that the magnetization may respond extremely fast. For example, in typical experiments [1, 4] having 40 fs — 1 ps pulses at 800 nm, with energy of 0.5 mJ that are focused to a spot size of ~0.5 mm2, the peak magnetic flux density can be as high as ~ 5 T, for which the corresponding Gilbert relaxation time reduces to tens of picoseconds in typical ferromagnets.In the following, the inventors show that ultrashort optical pulses may control the magnetization state by merely considering the optical magnetic field in the Landau- Lifshitz-Gilbert (LLG) equation. The principle behind the interaction is that the magnetization is incrementally affected within each optical cycle, such that a significant net torque can build up over the entire pulse duration in typical experimental conditions. The inventors find that the strength of the interaction is determined by = ccyH / fopt, where foptand a are the angular optical frequency and the Gilbert damping, respectively,and y is the gyromagnetic ratio. Accordingly, the loss of spin angular momentum to the lattice is key to the interaction. Moreover, it is shown that for circularly polarized (CP) pulses, the polarity of the optically induced torque is determined by the optical helicity. From a quantitative analysis, the inventors find that a sizable effective out-of-plane field is generated, which is comparable to that measured experimentally in ferromagnet / heavy- metal (FM / HM) material systems [5], However, the calculations indicate that an additional in-plane field is required to explain the experimental observations such as the optical spin transfer torque (OSTT). The inventors’ results provide an additional torque to the AO-HDS [1, 3, 6] that has been considered on grounds of thermal [7,8], photomagnetic [9], and optomagnetic [5] mechanisms. The critical role of a brings an additional explanation as to why an helicity-dependent torque is found in a variety of material systems that consist of heavy metals, such as Pt and Pd

[0003] , which are excellent absorbers of spin angular momentum.The LLG equation is typically not applied in the optical limit, and hence requires an alternative mathematical framework whose principles are adopted from the Bloch equations for semiconductor lasers [10,11], The inventors exploit the analogy between the magnetization state and the Bloch vector of a two-level system (TLS) [12-14] by transforming the LLG equation under a time-varying magnetic field excitation to the dynamical Maxwell-Bloch (MB) equations in the presence of an electrical carrier injection. In this transformation, the +z and — z components of the magnetization are mapped to the occupation of the ground and excited states of the TLS so that the reversal of the magnetization is described in terms of population transfer between the states.In the following description, the LLG equation is transformed to the density matrix equations of a TLS. Then, the mathematical form of a time-dependent magnetic field in the LLG equation, Hpumpis identified and is mapped to a time-independent carrier injection rate into the TLS. Such excitation induces a population transfer that varies linearly in time, and accordingly to a magnetization switching profile that is also linear in time. The mathematical Hpumpfield emerges naturally as a temporal impulselike excitation. The inventors then show that when a is sizable, Hpumpacquires a CP component whose handedness is determined by the direction of the switching. By substituting Hpumpfor an experimentally realistic picosecond CP Gaussian optical magnetic pulse, it is shown that it can also exert a net torque on the magnetization. In thiscase as well, the helicity determines the polarity of the torque. Finally, a quantitative analysis that is based on experimental data is presented [5],I: Derivation of Hpump^The LLG equation describing the dynamics of the magnetization, M, where the losses are introduced in the Landau-Lifshitz form is given by:Here Msand H are the magnetization saturation and the time dependent externally applied magnetic field, respectively. The inventors define by:(2)and in addition, where K and K0can be regarded as effective AC and DC magnetic fields acting on M, respectively. The inventors transform M to the density matrix elements of the Bloch state in the TLS picture having energy quantization along z by substituting the longitudinal component of M for the population difference,and the transverse components for the off-diagonal term The normalization condition isP11 + P22=Ms. Under this transformation, the LLG equation takes the form:Equation (3) describes a general TLS subjected to an effective field via K and K0. It is compared to the Bloch equations describing a semiconductor laser that is electrically pumped

[0010] :In this reference model, and Λ2are injection rates of carriers to the ground and excited states of the TLS, respectively. They are assumed to be time independent and represent a constant injection of carriers from an undepleted reservoir

[0010] , Yi and y2are the relaxation rates of the ground and excited states, and Yinh is the decoherence rate due to an inhomogeneous broadening. k12is the interaction term and ωTLSis the resonancefrequency of the TLS. Typically, ωTLSrepresents a time-independent interband energy gap, where h is the reduced Planck’s constant. However, here can depend on time.Fig. 5A illustrates schematically the analogy between the magnetization dynamics and the electrically pumped TLS. From Eqs. (3) and (4) the connection between the LLG equation expressed in the density matrix form and the model of the electrically pumped TLS is found:The pumping of the excited and ground states by the constantand Λ2rates implies that the reversal of the magnetization along the + z direction is linear in time. Using Eq. (5) K is found, and hence a field H, that produces suchand Λ2. The application of such a field as the sole excitation in the LLG equation results in yi = y2= V12= 0, and consequentlyThe inventors define this field as Hpump:Hpumpdepends on the temporal state of M while is theeffective field strength parameter. Applying such Hpumprequires to know a-priori the state of M, therefore it is referred to as a mathematical field. Hpumpiand Hpumpiinduce a linear transition of M towards the -z and +z direction, respectively. The constant carrier injection rate in the Bloch picture requires that Hpumpdiverges as M reaches the poles of the Bloch sphere.Fig. 5B presents the outcome of the application of Hpumpby numerically integrating the LLG equation. M was initialized in the x direction, so that Hpumpis polarized in the y direction and drives M in the z direction. Fig. 5B illustrates H(t), Mz(t), and the z torque, (— M X H) for alternating Hpumpiand Hpumpithat switch M between +Msz. The magnitude of Apdetermines the switching time, chosen hereto describe a picosecond regime. Equation (5) yields:in which Mzis driven from Mz= 0 to Mz= +MS(for derivation, see Appendix A below).It is seen that (— M X H) is constant when Hpumpior Hpumpiare applied so that the switching profile of Mzis linear in time. It is also seen that Hpumprequires that \H | diverge as Mzapproaches ±MS, which is not experimentally feasible.To account for a more realistic excitation, as exemplified in Fig. 5C, the inventors simulated a pulse whose trailing edge was taken as a reflection in time of Hpump, and that is shorter by an order of magnitude as compared to the leading edge. In this case H A Hpumpand does not induce a transition so that M remains in its final state when H is eventually turned off.II: Effect of the Gilbert damping on HpumpThe polarization state of Hpumpis determined from the polarization state of the transverse components of M. Particularly, if Mx(t) and My(t) follow a circular trajectory, HpUmpi,i- acquires a CP component as readily seen from Eq. (6). In Figs. 5B and 5C, a was relatively small, so that the damping torque was negligible and M remained in the x — z plane. Therefore, Hpumpremained linearly polarized in y.Next, the inventors show that for larger a, My(f) becomes appreciable such that HpUmpi,i- acquires an additional CP component. This result emerges naturally from the Bloch picture: it should be noted that the transverse components of M are expressed by the off-diagonal density matrix element, p12= (Mx— jMy^ / 2Ms. According to Eq. (4), p12oscillates at <nTLSand decays at the rate y^, whereas the sign of <nTLSdetermines the handedness of the transverse components of M. Namely, the ratio between <nTLSand yinhdetermines the magnitude of the circular component in thetrajectory.Under the application of Hpump, Eq. (5) yieldsreadily showing that \^TLs / Yinh\= aMs / Mzincreases with a, so that Hpumpacquires an additional CP component (see Appendix B below for full derivation).Figs. 6A and 6B illustrate these results. Fig. 6A presents the components of M(t) for the same simulation in Fig. 5B. It is seen that My(t) is negligible and thus Hpumpremains linearly polarized. When a is increased, an elliptical trajectory of M in the x — y plane emerges, while the constant transition rate of Mzpersists as illustrated in Fig. 6B. In this case, Hpumpacquires a right-CP (RCP) or left-CP (LCP) component depending on the choice of Hpump ior HpumpIII: Interaction with optical CP Gaussian pulsesThe coupling between the handedness and reversal direction in an ultrashort excitation is reminiscent of the switching reported in AO-HDS experiments [1] and emerges naturally in the model described herein. These results call to examine the interaction of the CP magnetic field of a short optical pulse with M. Fig. 7A presents the calculation for experimentally realistic settings following Ref. [4], where only the optical magnetic field is substituted into the LLG equation. The results are shown for an 800 nm optical magnetic field of an RCP Gaussian optical pulse modeled by Hopt(t) = Hpeak• The pulse has a duration determined by Tp, an angular0 / frequency <nopt, and a peak amplitude Hpeakthat is reached at t = tpeak. In the simulations Tp= 3 psec and tpeak= 10 psec. The pulse energy was ~ 5 pj and assumed to be focused to a spot size of ~ 100 pm2, for which Hpeak= 8 • 106Alm. Such spot size is much larger than typical size of a domain wall, therefore, the exchange energy is accounted for in the macrospin approximation. Here a = 0.035 is taken, which is typical for Pt / Co based systems [3], For such conditions, the Gilbert relaxation time corresponding to Hpeakis It is readily seen that for suchTathe magnetization responds within the duration of the optical pulse, indicating that the interaction between the optical pulse and M becomes possible by the LLG equation. Following the interaction, Mzis given by:namely a sizable net longitudinal torque results, which builds up from cycle to cycle of the optical radiation. This torque is not affected significantly by the anisotropy field, as discussed below in Appendix C.It should be emphasized that this mechanism is fundamentally different from the precessional switching mechanism by an optically induced DC longitudinal field. Such field can be generated, for example, by the inverse Faraday effect (IFE) which arises from the optical electrical field in contrast to the optical magnetic field considered for the purposes of the present disclosure. An equivalent effective DC magnetic field, B y, required for such transition within 10 psec is estimated to be ~ 50 mT (see Appendix C below).In agreement with the prediction of the TLS model, pulses of the opposite helicity induce an opposite transition as shown in Fig. 7B. The strength of the interaction depends on the ability of M to decay towards the oscillating optical magnetic field within the optical cycle. Hence, the magnitude of Tais key to the interaction. Accordingly, for a given pulse duration, the inventors define the interaction strength parameter which expresses the ratio between Taand the optical cycle andis 2.5 • 10-4in Fig. 7A.IV: Dynamics in the p -> 1 limitThe principles of the interaction can be better understood at the limit where i] -> 1 and for which the interaction can be described analytically. To this end, p is set to p = 1 so that the Gilbert relaxation time equals the optical cycle. The higher optical magnetic fields required for this limit are achievable using conventional amplified femtosecond lasers, for example by focusing a ~ 5 mJ pulse into a spot size of ~ 1 pm2. However, in practical experiments such pulses surpass the typical damage threshold of the metallic film. Nevertheless, the study of the LLG equation in this limit is instructive.Fig. 7C illustrates the results for an RCP Hoptpulse of a duration of 20 fsec determined by the full width at half-maximum of the intensity. Fig. 7C reveals the different stages of the interaction. During the leading edge, for t < ~ 40 fsec, the relative phase between Hoptand M seems arbitrary. As tpeakis reached, the Gilbert relaxation time becomes as short as the optical cycle, allowing M to follow Hoptuntil it is entirely locked to Hopt. In this case, M undergoes a right-circular trajectory about z. The switching of M takes place at the final stage of the interaction: During the trailing edge of the pulse, the amplitude of Hoptreduces and Taextends, thereby releasing the locking between M and Hopt. In this case, the switching profile of Mzis monotonic linear-like in time, closely resembling the transition stemming from a constant carrier injection rate in the Bloch picture.The optically induced transition can be described analytically following the calculation presented below in Appendix D, from which the transition rate is found:where is the value of Hpeakat η = 1.The rate r / Msis plotted as well in Fig. 7C and reproduces the numerical calculation, f depends on the ratio between Hpeakand Hthand is only weekly dependent on Hpeak. Namely, when Hpeak» Hth, the circular trajectory of M in the x — y plane persists longer after tpeak, but as the amplitude of the pulse decays below H M isdriven out of the x — y plane and the reversal takes place (see Appendix E below). This analysis also holds for LCP pulses, which result in an opposite reversal of M, as shown in Fig. 7D.In the following, the theoretical predictions presented above are compared with experimental results. η describes the efficiency of the interaction, namely, the ability of M to follow Hopt. When η « 1, as in the case of experimentally realistic intensities, the transition is partial as seen in Figs. 7A and 7B. In this case, an incremental torque acts on the magnetization within each optical cycle and builds up to a sizeable effective torque over the pulse duration. This illustrates the pivotal role of a since and is explored indetail in Appendix E.Interestingly, the AO-HDS effect was found in a variety of material systems that included Pt, which was introduced to induce a perpendicular magnetic anisotropy by the Pt / Co interface. However, Pt is also well known to be an efficient sink for spin angular momentum

[0017] , therefore it also increases a and enhances the optically induced torque according to the LLG equation.The measured time-resolved magnetization dynamics [5] provide quantitative data for testing the calculations performed by the inventors, as presented above. To this end, the inventors simulate an optical pulse having a fluence of 2.35 mJ / cm2and thesame sample parameters of the Co / Pt and Fe / Pt systems of Ref. [5] (Appendix C). From the response of My,is estimated [5]= 1 mT.Following similar analysis, the inventors find from their calculations that which is of the same order of magnitude. Ref. [5] further calculatedinduced by the IFE from the theories by Mondal

[0018] and others, and found a largerange of predicted~ 3 • 10-6— 40 T for the same conditions. Additionally, based on first-principles electronic structure calculations and the Keldysh nonequilibrium formalism, Ref. [5] estimated~ 1.5 — 20 mT. Thus, it is seen that the effective transverse torque emerging from the LLG equation is of comparable magnitude to that generated by the IFE.In a similar manner, an effective transverse field B^ can also be evaluated from the Mzdynamics. From the experimental data presented by Ref. [5], B^ is found to be in the range of ~ 0.05 — 0.87 mT for the various Co, Fe, and Ni based samples. In the calculations performed by the inventors B^ = 0.014 mT is found. Namely, an additional contribution to B^ should be accounted for. It was found that the electrical field associated with the magnetic field of the typical ultrashort pulses affects the electronic band structure. Consequently, the resultant nonequilibrium Keldysh states were shown to induce an OSTT wherein spin-polarized photo-carriers are generated according to the optical selection rules and contribute to B^ . Namely, the helicity dependent torque stemming from the calculations of the present disclosure should be considered alongside the IFE and OSTT mechanisms. Considering the LLG equation, SOC also enhances a and consequently also the efficiency parameter 77, resulting in a larger optically induced torque.Thus, the inventors demonstrated that the control of the magnetization of SOC- structure by an optical field arises from first principles by introducing the magnetic part of the optical radiation to the LLG equation. The principle of the interaction is that the magnetization is incrementally affected within each optical cycle such that a significant net torque can build up over the entire pulse duration. This was seen from the comparison between the experimentally realistic case where η « 1 and the case of η = 1. The process is independent of resonance conditions and is enhanced with increasing magnetic field amplitude and Gilbert damping. Using the TLS model, the inventors demonstrated thecoupling between the optical helicity state and the polarity of the longitudinal torque. A quantitative analysis of the optically induced torque revealed that it can be comparable to that generated by the IFE, and further stressed the important role of the OSTT. These results illustrate the generality of the LLG equation to the optical limit in the interaction between optical magnetic fields and spins in solids.Appendix A: Magnetization switching using HpumpThe inventors start with the calculation of the time duration ΔTduring which the Hpump- fields have to be applied in order to reverse the magnetization state, i.e. to drive Mzfrom Mz= 0 to Mz= Ms(in the manuscript M is initialized in the x direction). Assuming that Hpumpin Eq. (6) above is the only excitation acting on M, it follows that:Under the application of Hpumpfrom Eq. (6) above, Λ1= — A2, so that: (51.2)Both sides are integrated, for the duration ΛTduring which Mzincreases from 0 to Ms: (51.3)The right-hand-side is simply multiplied by AT, as Axis a constant: (51.4)Λxis expressed using Λp: (51.5)Finally: (51.6)The parameters of the simulations of Figs. 5A-5C and Figs. 6A-6B described above were chosen to model a realistic NM-FM bilayer sample such as the Pt / CoFeB system

[0019] with a = 0.025, thickness of the FM layer of tFM= 12 A and saturation magnetization of Ms= 3 • 105A / m. In Figs. 7A-7D, a = 0.035, which is typical for Pt / Co based systems

[0020] Appendix B: Calculation of the TLS termsThe procedure described in Eq. (5) above is implemented in order to derive expression for the TLS terms At, A2, y1y2, yinh, ωTLS, V12as a function of terms from the LEGS equation M, a, and Ap. The field Hpumpfrom Eq. (6) above has the following form:The "±" sign notation used herein correspond to the application of either Hpumpiror Hpump, respectively.The inventors start with the Generalized Heff field (Eq. (2) above):In components form it takes the following form:Next, K and K0are calculated similarly to the description above:Before starting the calculations, a useful identity should be pointed out:Now, the calculation is started in order to express the TLS terms Λ1and Λ2from the rate equation of p11(Eq. (3) above):Using the identity from Eq. S3.6:(S2'9)Similarly, for p22:(52'10)Using Eq. (4) above:Consequently, the TLS terms Λt, Λ2, y17Y2,V12are expressed:Next, the two remaining TLS terms ωTLSand yinhare expressed using the rate equation of p12in Eq. (3) above:(S2.ll)Inserting K and K0from Eq. S3.4 and S3.5:(S2.12)Reformulating the expression with p12:Using Eq. (4) above:Consequently, the TLS terms and yinhare expressed as:Appendix C: Evaluation of the effective induced fieldFollowing Ref. [5], the effective field is evaluated along — z from the small angle dynamics of Myby the effect of the field-like torque:On the other hand, the effective field can also be evaluated from the dynamics ofMzby the effect of a damping-like torque:For the case of Fig. 7A, Eq. S3.4 is used to evaluate:In Fig. 8 the action of the mechanism presented here is compared to that demonstrated by Choi at. al. [5] for a lOnm Co / 4nm Pt sample. Fig. 8 presents the optically induced dynamics of Myand Mz. The inventors introduce an RCP pulse to the LLG equation and set Δtpuise= 1.1 ps, tpeak= 2.5 ps and a = 0.025. In Fig. 8 it is found that introducing a CP optical field of 0.3 T in the LLG equation results inThe influence of the magnetic anisotropy on Beff(primary torque) was examined as well. To this end, the inventors introduced the anisotropy field Hanis= —Mzz to the LLG equation in addition to the optical pulse simulated in Fig. 7A.Figs. 9A and 9B readily show that the longitudinal torque induced by the optical pulse remains unaffected by Hanis. The change in Beff(primarytOrque)wasfound to be smaller than 10-4percent.Appendix D: Derivation of F / MsThe optically induced transition, for the case of η > 1, can be described analytically by making the following assumptions. To this end, Hpeakcorresponding to η = 1 is defined by It is first assumed that M is already locked to Hoptatt = tpeakand precesses in the x — y plane, and that the switching is initiated when the power of the pulse reduces to half the power of electromagnetic radiation having \H | = Hth. This occurs when Hopt(f) reaches the magnitude of Hcrit= The inventors calculate the transition rate, T, from Mzwhen the z torque is maximal. This point is found to occur approximately when | Mz(t) | ~ 0.5Msat which |Hopt(t)| reduces to H1 / 2= 0.27Hthas shown in Fig. 10.The inventors consider the case of t > tpeak+ tcrit, where tcrit= and start by presenting the components offor the RCP and LCP pulses. It is assumed that Hpeak> Hthand accordingly M is locked to the optical pulse at t = tpeak, and starts to decay from the x — y plane only after t = tpeak + tcrit- H is assumed that Mxand Myhave Gaussian envelopes:for the RCP and LCP pulses, where tcritand TMdefine their Gaussian profile. TMis the relaxation rate of M from the CP motion, which is now calculated: At t = tpeak+ G / 2 ,Hopt(t) decreases to H1 / 2and |Mz(t) | reaches 0.5Ms, so thatIn this case:which determines TMby the relation:Finally, using the normalization condition of\ \ it is found thatThe inventors calculated the transition rate, f, by taking the slope of Mz(t) at t = peak +fi / 2> from which it is found that:Appendix E: Magnetization reversal induced by circularly polarized magnetic field pulses Fig. 11 presents a similar simulation to Fig. 7C with additional details on the torques.Figs. 12-15 present the magnetization switching induced by circularly polarized pulses, in the absence of other excitations. Figs. 12-15 illustrate the effect of different pulse amplitudes for LCP and RCP pulses. They clearly show that while the phase- locking condition H is fulfilled, the LCP pulses fully reverse themagnetization upwards while RCP pulses reverse it downwards. In Fig. 12 a = 0.025 while in Fig. 13 a = 0.0075. In this case, a smaller damping still results in reversal. However, since the damping is at the core of the interaction, for the case where a = 10-4no reversal is built from cycle to cycle for any pulse amplitude, as readily seen in Fig. 14. In Fig. 15 a = 0.025 and the timescale is enlarged by three orders of magnitude, namely to the ~30 psec duration, while the wavelength is increased to 1mm. In this case, the Hthamplitudes required for the full magnetization reversal are also lower by three orders of magnitude as compared to the ~30 fsec pulses in Figs. 12-15.In Figs. 16A-16C the pivotal role of a to the interaction is shown and simulate the same conditions as in Fig. 7A are simulated for different a values and for Hpeak= 7.3 • 107A I'm.. It is readily seen that the response is enhanced with <z, namely Mz / Ms= 0.014, 0.02, 0.034 for a = 0.025, 0.035 and 0.06, respectively.Thus, the disclosure presented above shows that a helicity-dependent optical torque emerges by merely considering a circularly-polarized (CP) optical magnetic field in the Landau-Lifshitz-Gilbert (LLG) equation. These results were utilized in the novel optical sensing technique and imaging system utilizing the same, as described above with the reference to Figs. 1 and 4A-4B.The inventors also demonstrated the relevance of the above effect to the microwave regime and considered field-free reversal schemes induced by CP microwave radiation and CP spin-transfer-torque. These schemes provide novel spintronics-based magnetic memory devices, as described above with reference to Figs. 1, 2A-2D and 3A- 3BIn the following, analysis of CP microwave radiation and CP STT is more specifically described. The inventors show that the torque induced by a CP excitation in the LLG equation also applies to the microwave (RF) regime and propose a field-free CP- RF based magnetization reversal scheme. The effect of the magnetic RF field, Hr^ on the magnetization, M, is examined by numerically integrating the LLG equation in which the losses are introduced in the Landau-Lifshitz form:where Msis magnetization saturation.Reference is made to Figs. 17A-17D. In Fig. 17A an RCP CW magnetic field excitation of frequency fRF= 1 GHz is simulated, where a = 0.025. The strength of the interaction, r / is set to r / = 1.5 X 10-2, which corresponds to a ~ 34 Oe amplitude. Similarly to the optical regime case, large-scale oscillations are induced and a net longitudinal torque results. In Fig. 17B M is initialized in the z direction, and a complete transition of M to the — z direction is achieved.The applicability of the theory extended by the inventors to the RF regime provides for a field-free reversal scheme induced by CP spin currents. In the case of a spin-transfer-torque (STT) excitation, the LLG equation is driven by a term of the following form:where S is the normalized spin polarization vector of the STT excitation and HSHE= | amplitude of the STT excitation generated by the spin Hall effect. Theparameters were chosen to model a realistic normal-metal ferromagnet (NM-FM) bilayer sample such as the Pt / CoFeB system

[0019] , with a spin Hall angle of ©SHE=0.15, FM layer thickness of tFM= 12 A and AC current density amplitude of Jc ac~ 2.5 X IO10A / m2. h is the reduced Planck constant and e is the electron charge.Fig. 17C shows simulation of an LCP CW STT excitation of frequency fRF=1 GHz under η = 1.5 X 10-2, for which |HSHE|~ 34 Oe. Similarly to Fig. 17A, large- scale oscillations and a longitudinal torque in the response are observed, where fenv= (see the following section). The polarity of the torque induced by CPSTT excitations is inversed as compared to that induced by CP radiation. The magnetization reversal depicted in Fig. 17C displays different characteristics to that in Figs. 17A and 17B: while the Mzprofile induced by radiation is nearly uniform throughout the process, the Mzprofile induced by STT becomes more pronounced as \MZ| increases. In order to further point out this discrepancy, in Fig. 17D M is initialized in the z direction. It is readily seen that the Mzprofile becomes more pronounced as \MZ\ increases and vanishes when \MZ\ -> 0.Fig. 18 presents the temporal evolution of M under pulsed microwave radiation \ STT excitations, for the linear \ elliptical \ circular polarization states of <p = 0°, 45°, ±90°. SRFis a 1 GHz STT excitation under r / = 2 x 10-2, generated by an ac charge current of Jc ac= 3.2 x 1010[A / m2]. HRFis a 1 GHz microwave field under r / =2 X 10-2. Similarly to Figs. 17A-17D, it is readily seen that also for pulsed excitations the longitudinal torque is maximal for CP excitations and vanishes for LP excitations.Figs. 19 and 20 show the temporal evolution of M driven by RCP \ LCP CW STT excitations in the absence of an external static field. The RF frequency is fRF= 1 GHz and 2 GHz, respectively. The initial state of M varies between the x, x + y + z, and the x + y — z direction, a varies between 0.025 and 0.05, r] varies between 2.5 x 10-3, 5 x 10-3, 10-2, 2 X 10-2corresponding to Jc ac~ 2 X 109— 3.2 X 1010[A / m2]. It is readily seen that fenvis independent of the initial states of M.Table 1 shows the calculated fenvas a function of TJ, a and fRF.Table 1.From Table 1, fenvis determined by whichcorresponds to 0 isthe amplitude of the STTexcitation generated by the spin Hall effect.In the following, the discrepancy in the reversal profile induced by CP radiation and CP STT is explained, using the analogy to the TLS Bloch vector formalism [ 12,14], To this end, M is transformed to the density matrix elements of a two-level-system (TLS) having energy quantization along z according to: Mz= p1 1— p22and p12= (Mx~ j My) / 2, where pxland p22are the occupation probabilities of the ground and excited states, respectively, and p12is the off-diagonal term of the density matrix. The normalization condition is pxl+ p22= Ms. Under this transformation, the LLG equation describes the dynamics of an effective TLS as follows

[0010] :In this reference model, and Λ2are injection rates of carriers to the ground and excited states of the TLS, respectively,and y2are the relaxation rates of the ground and excited states, and yinhis the decoherence rate due to an inhomogeneous broadening. aiTLSis the resonance frequency of the TLS, and V12is the interaction term. V12is able to induce a population transfer between p1;Land p22in the TLS picture, which corresponds to the evolution of Mzin the LLG equation.With the above transformation applied on Eq. (8), P12is given by:(the derivation is presented below in Appendix F), where / / (t) is the driving AC magnetic field. In this case, j hence follows the’amplitude of / / (t) throughout the interaction, independently of the temporal evolution of M.On the other hand, for an STT excitation described in Eq. (9), F12is given by:wherIn this case, namely thereby revealing that the reversal profile induced by CP STTbecomes more pronounced as |MZ| increases. Moreover, it is readily seen that a determines |F121 in the Mz-> 0 limit, namely it allows the transition to pass the xy plane.Thus, the inventors showed that the principles of the interaction of the magnetization with various circularly polarized excitations in the LLG equation, apply also to the microwave regime, and pave the way for energy-efficient CP microwave radiation \ STT driven reversal schemes without external field assistance. These schemes can advantageously be used in magnetic memory applications as exemplified inFigs. 3A-3B.Appendix F: Calculation of V12The procedure described in [ 12, 14] is implemented by the inventors in order to derive expression for the TLS term f12as a function of terms from the LLGS equation: M, a, Hx, Hyand HSHE X, HSHE Y.The definition of the generalized B' field is:In components form:Following [ 12, 14], K and KQare calculated:K and KQcan be regarded as effective AC and DC magnetic fields acting on M, respectively. Under K and K0, Eq. (10) is given by:Next, the calculation is started in order to express the TLS terms V12from the rate equation of p11by inserting K from Eq. (S4.3):Finally, one obtains:Similarly, for p22:Using Eq. (10):The TLS term V12is expressed:In the following, a relation between the measured resistance of the optical sensor (described above with reference to Figs. 4A-4F) with the incident light intensity is described.Fig. 21A illustrates the longitudinal (Tz) and transverse torques (Ty) acting on the FL. Overall, the change in the resistance ΔR of the spin valve or MTJ is proportional to the longitudinal torque Tz.For a pulsed optical excitation: (8)where zpis the pulse duration, IRCP— ILCPis the difference between the intensities of the RCP and LCP components of the beam, a is the Gilbert damping (stemming from the spin-orbit coupling), foptis the optical frequency, y is the gyromagnetic ratio, c is the speed of light, e is the natural exponent and Cois a proportion coefficient.For a CW excitation:(9)where tcwis the CW exposure duration.In the following, the longitudinal torque Tzis calculated.First, the inventors examine the effect of a single optical pulse on the magnetization, M, as illustrated in Fig. 21A. To this end, the LLG equation is numerically integrated, in which the losses are introduced in the Landau-Lifshitz form:(10)Here, Msis the saturation magnetization and y ' = y / ( 1 + α2). A right circularly- polarized (RCP) Gaussian pulse is applied of the formwhere Φ = 90°. The full-width at half maximum (FWHM) of the intensity isand peak amplitude Hpeakis reached at tpeak. Throughout the simulations, M is initialized in x and Ms= 3 X 105Alm. which is typical of Co based films.The inventors first examine the dependence of Tzon F where the latter is proportional to the product of the intensity and pulse duration by Tzisdetermined from the induced z component of M following the interaction and is represented in normalized units, Tz= Mz / Ms. Fig. 21B presents Tzas a function of 77, fortypical experimental conditions of a and the wavelength, λ. η is variedby sweeping over the relevant range of Hpeak. Fig. 21B readily shows that Tzis quadratic in η , namely, Tzis linear in the optical intensity, I. Fig. 21C illustrates the dependence of Tzon Tpfor a constant iy Tzis linear in Tpillustrating that Hoptinduces an optical torque that builds up with each optical cycle. A similar trend was reported experimentally in Refs. [27, 4], Since Tzscales with Hpeakand rp, it is concluded that Tzoc F. A linear dependence of the torque on F was also reported experimentally. Following a detailed analysis, as will be shown below, it is found thatwhere e is the natural exponent (throughout the description herein it is assumed that y ' « y). This relation also shows that the torque is enhanced with a and decreases with fopt. Interestingly, the AO-HDS was demonstrated in a variety of multi-layered material systems that consist of heavy metals such as Pt and Pd that possess large a.Next, the dependence of the optically induced torque on the polarization state is examined. Fig. 21D presents Tzas a function of the polarization state, 0. It is readily seen that Tzvanishes for LP beams (0 = 0°, 180°) whereas for CP beams (Φ = 90°, 270°) it is maximal. Such behavior is typical of AO-HDS and was reported experimentally in various works [4, 1], For a general polarization state, Tzoc — sin(0) which is proportional to IRCP— ILCP. Hence, Tzis determined by:where c is the speed of light.Next, the inventors show that the torque induced by a single pulse can be equivalently achieved by applying multiple pulses who’s total fluence equals that of the original pulse. Figs. 22A and 22B show the temporal evolution of the normalized magnetization m, m = M / Msunder various irradiation conditions. Fig. 22B shows the temporal response of M to 10 Hoptpulses for the same conditions of Fig. 22A each having a duration of rp / 10 and an arbitrary carrier phase. It is seen that each pulse exerts Tzsuch that following the entire interaction the accumulated torque is equal to the torque induced by the original single pulse simulated in Fig. 22A and is independent of the relative carrier phases.Fig. 22C presents the optical torque induced by multiple RCP Hoptpulses as a function of η and the number of applied pulses. In this general case,such that the optically-induced torque builds up with each applied pulse as also reported experimentally [27, 4], Since the total torque can be induced either by a single pulse or by multiple pulses, the inventors conclude that it is determined by the accumulated exposure time. This suggests that the effect is more general and may be also relevant for longer pulses, reaching the CW limit.The dynamics induced by a CW beam of a duration tcware depicted in Fig. 23. The inventors introduce an RCP CW beam, Hopt Cw( )at800 nm and tcw= 100 nsec and a = 0.025. The, simulation of Hopt cwcorresponding to a power of 5 mW focused to a diameter of 500 nm is performed. Under these settings, Hpeakwas ~ 10 mT for which η ~ 10-7. Fig. 23 reveals a similar accumulation of the torque as in Figs. 22A and 22B. A similar analysis as the one carried out for the pulsed excitations of Figs. 21B to 21D, reveals that the torque induced by a CW beam iswhereas for a general polarization state, it is proportional to IRCP— lLCP.In the following, the inventors describe the optical torque induced by a single pulse under parameter variation.Fig. 24A shows the heatmap of Tzafter the application of an RCP optical magnetic pulse in the LLG equation for 10-4< η < 2.5 x 10-3, a = 0.025, and = 800 nm.The heatmap is presented on a logarithmic scale for visibility. The amplitude of the pulse is is the magnetic field amplitude required for 77 = 1.Fig. 24B shows fitted matrix, readily showing the dependence of the optically-induced torque on the optical fluence, where C is a constant coefficient. The analysis over various a and A values yields where e is the natural exponent. The term e stemsfrom the temporal Gaussian envelope. Additionally, from this relation the inventors can quantitatively define a criterion for full reversal (i.e. Tz= 1), whereFig. 25 shows similar heatmaps of Tzafter the application of an RCPoptical magnetic pulse. Dashed curves correspond to the H criterion in every panel.Fig. 25 reveals that a similar behavior prevails for a variety of experimentally realistic a and A values.The inventors remark that the higher optical magnetic field amplitudes simulated in above ( η > ~ 10-2) are achievable using conventional amplified femtosecond lasers, for example by focusing a ~ 0.5 mJ pulse into a spot size of ~ 150 jim2. However, in practical experiments such pulses surpass the typical damage threshold of the metallic film. Nevertheless, the study of the LLG equation in this limit is instructive, as it highlights the fundamental principles of the interaction, which apply also for lower η values.Thus, the present disclosure provides a novel approach for controlling, inducing of and / or affecting magnetization change (e.g., magnetization reversal) by application of helical torque. The present disclosure presents the comprehensive theoretical support for this effect and describes and exemplifies specific devices based on the same. Such devices include sensors (e.g., optical sensors) or magnetic devices.

Claims

CLAIMS:

1. An electronic device comprising: at least one basic block, each of said at least one basic block comprising an active unit configured and operable to be responsive to one of circularly polarized electromagnetic field or circularly polarized spin current by a change in magnetization orientation in the active unit; and a control circuit configured and operable to carry out one of the following: (i) monitoring changes in at least one electrical property of the active unit to thereby monitor the change in magnetization orientation in the active unit in response to the circularly polarized electromagnetic field being applied to the active unit, or (ii) managing generation of the circularly polarized spin current in the active unit to thereby induce said change in the magnetization orientation in the active unit.

2. The electronic device according to claim 1, wherein each of said at least one basic block is configured for use with a magnetic unit.

3. The electronic device according to claim 1, wherein each of said at least one basic block is configured for use with a magnetic unit of a magnetic tunnel junction (MTJ) type.

4. The electronic device according to claim 2 or 3, wherein: said basic block is configured as an integrated structure comprising: said active unit comprising a ferromagnetic layer configured with an initial magnetization, and a helical torque generator layer structure interfacing with said ferromagnetic layer, said helical torque generator layer structure being made of an electrically conductive material composition possessing spin orbit coupling (SOC); said control circuit is configured and operable to provide a phase shifted AC current supply to the helical torque generator layer structure thereby producing the circularly polarized spin current therein passing to said ferromagnetic layer interfacing with the torque generator layer structure resulting in a helical torque effect inducing the change of magnetization orientation by magnetization reversal in the ferromagnetic layer.

5. The electronic device according to claim 3, wherein: said basic block is configured as an integrated structure comprising: said active unit comprising a ferromagnetic layer configured with an initial magnetization to serve as a free layer of the magnetic unit, anda helical torque generator layer structure interfacing with said ferromagnetic layer, said helical torque generator layer structure being made of an electrically conductive material composition possessing spin orbit coupling (SOC); said control circuit is configured and operable to provide a phase shifted AC current supply to the helical torque generator layer structure thereby producing the circularly polarized spin current therein passing to the free layer interfacing with the torque generator layer structure resulting in a helical torque effect inducing the change of magnetization orientation by magnetization reversal in the free layer.

6. The electronic device according to claim 1, wherein each of said at least one basic block is configured as a magnetic unit of a magnetic tunnel junction (MTJ) type.

7. The electronic device according to claim 6, wherein the basic block comprises: an integrated structure comprising: said active unit comprising a first ferromagnetic layer configured with an initial magnetization and operable as a free layer, an insulator layer, and a second ferromagnetic layer having fixed magnetization; and a helical torque generator layer structure interfacing with said free layer, said helical torque generator layer structure being made of an electrically conductive material composition possessing spin orbit coupling; and said control circuit is configured and operable to provide a phase shifted AC current supply to the helical torque generator layer structure thereby producing the circularly polarized spin current therein passing to the free layer interfacing with the torque generator layer structure resulting in a helical torque effect inducing the change of magnetization orientation by magnetization reversal in the free layer.

8. The electronic device according to claim 4 to 7, wherein said control circuit is further configured to supply DC current to the helical torque generator layer structure.

9. The electronic device according to claim 2, wherein: said basic block comprises: said active unit comprising a ferromagnetic layer configured with an initial magnetization, and a helical torque generator comprising an antenna unit formed by a pair of antenna elements located in a vicinity of said ferromagnetic layer; said control circuit is configured and operable to provide a phase shifted AC current supply to the antenna elements producing generation of the circularly polarizedelectromagnetic field, being an RF field, by the antenna unit thereby applying a helical torque to said ferromagnetic layer inducing the change of magnetization orientation by magnetization reversal in the ferromagnetic layer.

10. The electronic device according to claim 2, wherein said basic block comprises: said active unit comprising a first ferromagnetic layer having initial magnetization and being operable as a free layer, an insulator layer, and a second ferromagnetic layer having fixed magnetization; a helical torque generator comprising an antenna unit formed by a pair of antenna elements located in a vicinity of said first ferromagnetic layer; said control circuit is configured and operable to provide a phase shifted AC current supply to the antenna elements producing generation of the circularly polarized electromagnetic field, being an RF field, by the antenna unit thereby applying a helical torque to said first ferromagnetic layer inducing the change of magnetization orientation by magnetization reversal in the first ferromagnetic layer.

11. The electronic device of any one of claims 4 to 8, wherein said helical torque generator layer structure is made of at least one electrically conductive material composition comprising heavy atoms.

12. The electronic device of any one of claims 4 to 8, wherein said helical torque generator layer structure is made of at least one electrically conductive material composition comprising one or more heavy metals.

13. The electronic device of claim 11 or 12, wherein said helical torque generator layer structure is made of the at least one electrically conductive non-magnetic material composition possessing spin orbit coupling.

14. The electronic device according to claim 1, wherein each of said at least one basic block is configured as a sensor of electromagnetic radiation including at least one of optical radiation, RF radiation, THz radiation, X-ray radiation.

15. The electronic device according to claim 14, wherein: the active unit is an integrated structure configured as a magnetic tunnel junction (MTJ) structure comprising: a first layer, being either a ferromagnetic having an initial non-zero magnetization and operable as a free layer, an insulator layer, and a second ferromagnetic layer having fixed non-zero magnetization, the active unit being responsible to interaction with the circularly polarized electromagnetic field of anincident beam of electromagnetic radiation by the change in the magnetization orientation in the free layer; the control circuit is configured and operable to provide electric current supply to the active unit and performing said monitoring of changes in resistance of the active unit caused by the change in the magnetization orientation in the free layer, and extracting data indicative of intensity of the incident beam.

16. The electronic device according to claim 15, wherein said initial non-zero magnetization is of in-plane magnetization orientation.

17. The electronic device according to claim 15 or 16, wherein said active unit further comprises a circular polarizer assembly accommodated at a side of said first layer intended for exposure to interaction with the incident beam.

18. The electronic device according to claim 14, wherein: the active unit is an integrated structure comprising: a first layer being a nonmagnetic layer configured as a spin orbit coupling structure, an insulator layer, and a second ferromagnetic layer having fixed non-zero magnetization, the active unit being responsible to interaction with the circularly polarized electromagnetic field of an incident beam of the electromagnetic radiation by the change in the magnetization orientation in the first layer; the control circuit is configured and operable to provide electric current supply to the active unit and performing said monitoring of changes in resistance of the active unit caused by the change in the magnetization orientation in the first layer, and extracting data indicative of intensity of the incident beam.

19. The electronic device according to claim 18, wherein said active unit further comprises a circular polarizer assembly accommodated at a side of said first layer intended for exposure to interaction with the incident beam.

20. The electronic device according to claim 14, wherein the active unit is an integrated structure configured as a Spin Valve structure comprising: a first ferromagnetic layer having an initial non-zero magnetization, and electrically-conductive layer, and a second ferromagnetic layer having fixed non-zero magnetization, the active unit being responsible to interaction with the circularly polarized electromagnetic field of an incident beam of the electromagnetic radiation by the change in the magnetization orientation in the first ferromagnetic layer;the control circuit is configured and operable to provide electric current supply to the active unit and performing said monitoring of changes in giant magnetoresistance of the active unit caused by the change in the magnetization orientation in the first layer, and extracting data indicative of intensity of the incident beam.

21. The electronic device according to claim 20, wherein said initial non-zero magnetization is of in-plane magnetization orientation.

22. The electronic device according to claim 20 or 21, wherein said active unit further comprises a circular polarizer assembly accommodated at a side of said first layer intended for exposure to interaction with the incident beam.

23. The electronic device according to claim 14, wherein said active unit comprises a Hall element made of one or more electrically conductive material compositions possessing spin orbit coupling (SOC); and said control circuit is configured and operable to monitor voltage changes in the active unit to thereby determine the change in the magnetization in the Hall element in response to the circularly polarized electromagnetic field of an incident beam of the electromagnetic radiation on the active unit, and to extract data indicative of intensity of the incident beam.

24. The electronic device according to claim 23, wherein said active unit further comprises a circular polarizer assembly accommodated at a side of the Hall element intended for exposure to the incident beam of the electromagnetic radiation.

25. The electronic device of claim 23 or 24, wherein said Hall element is made of the at least one electrically conductive non-magnetic material composition possessing spin orbit coupling.

26. The electronic device of any one of claims 14 to 25, comprising an integrated layer structure comprising an array of spaced-apart individually operable active units, each connected to the respective control circuit.

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