Spin current and magnetoresistance from orbital hall effect

Abstract

Devices that sense and manipulate magnetic fields based on spin current interactions independent of the spin Hall effect (SHE) in heavy metals. Spin current is generated in ordinary metals through a conversion of out-of-plane orbital current induced by the orbital Hall effect (OHE). The conversion from orbital current to spin current occurs in thin heavy metal layers (a few atomic layers thick), thus greatly reducing the need for heavy metals by replacing them with ordinary metals. Device applications include magnetoresistive sensors for detecting and measuring magnetic fields, and magnetic tunnel junction data storage cells.

Description

Field of the invention

[0001] The present invention relates to the field of spin transport electronics, and in particular to conversion of orbital current to spin current associated with the orbital Hall effect. BACKGROUND

[0003] The field of spin transport electronics, also known as spin electronics or spintronics, has many practical applications, non-limiting examples of which include magnetoresistive devices for reading magnetically encoded data storage media; and magnetoresistive random access memory for computers.

[0004] The spin Hall effect (SHE) has been used to electrically manipulate electron spin in various spintronic applications. Spin current involves alignment of intrinsic electron spin and has a specified orientation. A notable material that exhibits strong SHE behavior is heavy metal.

[0005] Currently, spin Hall effect devices rely on heavy metals to provide spin current. However, in some cases, it is desirable to reduce the reliance on heavy metals by utilizing ordinary metals to provide spin current in the devices, while reducing the extent of heavy metals required. Embodiments of the present invention achieve this goal. SUMMARY

[0007] Embodiments of the present invention provide devices for sensing and manipulating magnetic fields based on spin current interactions independent of the spin Hall effect (SHE) in heavy metals. According to various embodiments of the present invention, spin current is generated by converting out-of-plane orbital current produced by the orbital Hall effect (OHE) in ordinary metals. The OHE does not rely on spin-orbit coupling, and the orbital current is produced in ordinary metals.

[0008] The term "heavy metal" in this context refers to metallic elements having a 5d electron shell, including but not limited to, in particular: platinum (Pt); tungsten (W); and tantalum (Ta). Conversely, the term "ordinary metal" in this context refers to metallic elements lacking a 5d electron shell and having at most a 3d or 3d / 4d electron shell, or lacking a d shell altogether. Ordinary metals include but are not limited to, in particular: copper (Cu); and aluminum (Al). Heavy metals exhibit strong spin-orbit coupling (SOC), while ordinary metals exhibit weak spin-orbit coupling.

[0009] Orbital current involves alignment of atomic electron orbital motion, as opposed to the intrinsic spin of the electron. Orbital current has a specified orientation. Embodiments of the present invention provide conversion from orbital current to spin current via a thin layer of heavy metal (typically only a few atomic layers thick (in the nanometer range)) that overlies a common metal planar component, thereby significantly reducing the need for heavy metal by replacing much of it with common metal. The term "overlies" in this context means that the thin layer abuts the surface of the metal planar component and is in electrical contact therewith. As disclosed herein, non-limiting applications of devices according to the present invention include magnetoresistive sensors for detecting and measuring magnetic fields, and magnetic tunnel junction data storage.

[0010] "Charge current" in this context refers to the flow of electric charge in a conductor as encountered in ordinary electrical circuits.

[0011] Thus, embodiments of the present invention significantly reduce the need for heavy metal by providing orbital current with common metal, and then converting the orbital current to spin current using minimal heavy metal.

[0012] Thus, in embodiments of the present invention, there is provided a device for generating spin current, the device comprising: (a) a planar component for generating out-of-plane orbital current via orbital Hall effect (OHE) of in-plane charge current flowing within the planar component, (b) wherein the planar component is substantially comprised of common metal lacking a 5d electron shell; (c) a layer of heavy metal in electrical contact with a surface of the planar component for converting the out-of-plane orbital current to out-of-plane spin current, (d) wherein the heavy metal has a 5d electron shell. BRIEF DESCRIPTION OF DRAWINGS

[0014] The disclosed subject matter can be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings in which:

[0015] FIG. 1 conceptually illustrates a prior art device configuration that utilizes a heavy metal planar component to provide out-of-plane spin current from in-plane charge current.

[0016] Figure 2 A device component configuration according to embodiments of the present invention is conceptually illustrated in which the extent of heavy metal is significantly reduced, and in which the metal planar component for providing out-of-plane spin current is substantially comprised of common metal through which in-plane charge current flows.

[0017] FIG. 3 conceptually illustrates a prior art device configuration that utilizes a heavy metal planar component to provide out-of-plane spin current from in-plane charge current.

[0018] FIG. 4 conceptually illustrates a prior art magnetic tunnel junction device that provides out-of-plane spin current switching by a heavy metal planar component.

[0019] Figure 5A magnetic field sensor device for detecting and measuring the rotation of a permanent magnetic field caused by an external magnetic field according to an embodiment of the application is conceptually illustrated.

[0020] Figure 6A Establishing a magnetic field having a first orientation in a permanent magnet by a device according to an embodiment of the application is conceptually illustrated.

[0021] Figure 6B Establishing a magnetic field having a second orientation in a permanent magnet of a device according to this embodiment is conceptually illustrated. Figure 6A

[0022] Figure 7 A magnetic tunnel junction device switched by out-of-plane orbit to spin current conversion according to an embodiment of the application is conceptually illustrated.

[0023] For the sake of simplicity and clarity of illustration, the items illustrated in the figures are not necessarily drawn to scale, and the dimensions of some items relative to other items can be exaggerated. Furthermore, reference signs can be repeated in the figures to indicate corresponding or analogous items.

[0024] Detailed description of the application

[0025] Fig. 1 conceptually illustrates a prior art device configuration 100 utilizing a heavy metal planar component 101 for generating an out-of-plane spin current 103 from an in-plane charge current 102 flowing through the heavy metal planar component 101. As previously mentioned, platinum, tungsten and tantalum are commonly used as the heavy metal of the planar component 101.

[0026] The term "planar component" in this context denotes a three-dimensional component having at least one face that is substantially in the form of a plane and has a surface area sufficient to abut a corresponding face of another component. A planar component has an "in-plane" axis that is located inside the component and oriented parallel to the surface of the face, and an "out-of-plane" axis that is at least partially located outside the component and oriented perpendicular to the surface of the face. In this context, the direction of flow of a charge current within a planar component is referenced to the in-plane axis of the planar component; in this context, the orientation of a spin current and the orientation of an orbital current are referenced to the out-of-plane axis of the planar component.

[0027] Figure 2 ​A device component configuration 200 according to an embodiment of the present application is conceptually illustrated, in which the extent of heavy metal is substantially reduced to a thin layer 201. A planar component 251 of ordinary metal is fabricated and constitutes a substantial portion of the body of the device 200, such that the layer 201 is in electrical contact with the top surface of the planar component 251. According to the present application, an in-plane charge current 202 flowing through the ordinary metal 251 generates an out-of-plane orbital current 205 via the orbital Hall effect (OHE), while the thin layer 201 converts the out-of-plane orbital current 205 to an out-of-plane spin current 203 via spin-orbit coupling. In related embodiments, the heavy metal layer 201 is only a few atoms thick - a total thickness of 1 nanometer is generally sufficient. (As before, the drawing is not intended to be drawn to scale, and the thin layer 201 is exaggerated in size in the drawing for clarity.) Thus, by utilizing ordinary metal to conduct the charge current 202, embodiments of the present application provide a substantial reduction in the amount of heavy metal required to generate an out-of-plane spin current. In other embodiments, copper and aluminum are used for the ordinary metal 251.

[0028] FIG. 3 conceptually illustrates a prior art device configuration 300 that utilizes a heavy metal planar component 101 as shown in FIG. 1 to provide an out-of-plane spin current 203 from an in-plane charge current 202. In this embodiment, the out-of-plane spin current 203 controls the magnetic field orientation 302 of a permanent magnet 301 positioned above the heavy metal planar component 101.

[0029] Figure 4 conceptually illustrates a prior art three-terminal magnetic tunnel junction device 400. A magnetic tunnel junction 410 (MTJ) combines a ferromagnetic reference layer 411 over a thin insulating layer 412, which is under a ferromagnetic free layer 213. The insulating layer 412 is typically only a few nanometers thick, such that electrons can tunnel through the insulating layer 412 and pass between the reference layer 411 and the free layer 413. The reference layer 411 maintains magnetization in a direction 431, but the magnetization of the free layer 413 can be switched between a direction 432, which is parallel to the direction 431, and a direction 433, which is anti-parallel to the direction 431. When the free layer 413 is magnetized in the direction 432, which is parallel to the direction 431, electrons tunnel through the insulating layer 412 with high statistical probability, thereby establishing a low resistance conductive path between the reference layer 411 and the free layer 413. However, when the free layer 413 is magnetized in the direction 433, which is anti-parallel to the direction 431, electrons tunnel through the insulating layer 412 with low statistical probability, thereby establishing a high resistance between the reference layer 411 and the free layer 413. Thus, switching the magnetization direction of the free layer 413 effectively switches the MTJ 410 between a conductive state and a substantially non-conductive state. In the device 400, the magnetization direction of the free layer 413 is switched by switching the out-of-plane spin current 422 provided by the heavy metal planar component 401, which is a result of the spin Hall effect in response to an in-plane charge current 420 injected through the heavy metal planar component 401. The direction of the charge current flow 420 controls the direction of the out-of-plane spin current 422, and thus the conductive state of the MTJ 410. A first electrical terminal T1 402 is connected to the reference layer 411; a second electrical terminal T2 403 is connected to one side of the heavy metal planar component 401; and a third electrical terminal T3 404 is connected to the other side of the heavy metal planar component 401. Thus, the magnitude and direction of the in-plane charge current 420 is given by the current flowing between the terminals T2 403 and T3 404. The conductive state of the MTJ 410 can be externally detected by sensing the resistance between the terminal T1 402 and the terminal T2 403 or the terminal T3 404. A non-limiting application of the device 400 is for data storage, where a single data bit can be represented by the conductive state of the MTJ 410. According to the desired bit value to be written, the bit is written by passing a current pulse in the left or right direction between the terminals T2 403 and T3 404; and the bit is read by sensing the resistance between the terminal T1 402 and the terminal T2 403 or the terminal T3 404.

[0030] Figure 5 A two-terminal device 500 according to an embodiment of the present application is conceptually illustrated for detecting and measuring the rotation of a permanent magnetic field 502 in a ferromagnetic material 501 caused by an external magnetic field 510. In a non-limiting example, the external magnetic field 510 corresponds to the state of a magnetic data storage medium, and inFigure 5 The device shown in Fig. 6 and described herein reads data from a magnetic data storage medium.

[0031] The present embodiment provides a magnetic field sensor as described below: as Figure 2 shown and disclosed above, the planar piece 251 of ordinary metal is covered with a thin layer 201 of heavy metal (only a few atomic layers thick). In Figure 5 Fig. 6, a first electrical terminal T1503 connected to one side of the planar piece 251 and a second electrical terminal T2504 connected to the other side of the planar piece 251 are shown, which allow sensing the electrical resistance of the planar piece 251 when an in-plane charge current 505 flows through the ordinary metal of the planar piece 251 and establishes an out-of-plane orbital current 506. Due to the high spin-orbit coupling of the layer 201, the orbital current 506 is coupled to an out-of-plane spin current 507. The spin current 507 is influenced by the rotating magnetic field 502, which in turn influences the coupled orbital current 506, and which in turn influences the in-plane charge current 505. The influence on the in-plane charge current 505 is detected and measured (e.g. using a resistance measuring device 520) by measuring the electrical resistance (in Ohms (Q)) between the terminals T1503 and T2504. Since the rotation of the magnetic field 502 is a function of the strength and orientation of the external magnetic field 510, the external magnetic field 510 strength and orientation can also be measured from the electrical resistance between the terminals T1503 and T2504 (e.g. using the device 520), and thus Figure 5 The device of Fig. 6 provides a magnetic field sensor.

[0032] Figure 6A Fig. 6 conceptually shows the establishment of a magnetic field 602 with upward orientation in a permanent magnet 601 by the device 600 according to an embodiment of the present invention. When an in-plane charge current 605 flows through the ordinary metal planar piece 251 in a direction from left to right, an out-of-plane orbital current 606 is established (which is oriented in a direction upward through the heavy metal layer 201). The heavy metal layer 201 converts the orbital current 606 into an out-of-plane spin current 607, which is also oriented in the upward direction. The out-of-plane spin current 607 in turn generates the magnetic field 602, which is also oriented in the upward direction.

[0033] Figure 6B Fig. 7 conceptually shows the establishment of a magnetic field 612 with downward orientation in a permanent magnet 601 by the device 600 according to this same embodiment. When an in-plane charge current 615 flows through the ordinary metal planar piece 251 in a direction from right to left, an out-of-plane orbital current 616 is established (which is oriented in a direction downward through the heavy metal layer 201). The heavy metal layer 201 converts the orbital current 616 into an out-of-plane spin current 617, which is also oriented in the downward direction. The out-of-plane spin current 617 in turn generates the magnetic field 612, which is also oriented in the downward direction.

[0034] Figure 7 A magnetic tunnel junction device 700 is conceptually illustrated that is switched by out-of-plane orbital-to-spin current conversion according to an embodiment of the application. The MJT 710 combines a ferromagnetic reference layer 711 over a thin insulating layer 712, which is under a ferromagnetic free layer 713. The insulating layer 712 is typically only a few nanometers thick, so that electrons can tunnel between the reference layer 711 and the free layer 713 across the insulating layer 712. The reference layer 711 is held magnetized in a direction 731, but the magnetization of the free layer 713 can be switched between a direction 732 that is parallel to the direction 731 and a direction 733 that is anti-parallel to the direction 731. When the free layer 713 is magnetized in the direction 732 that is parallel to the direction 731, electrons tunnel across the insulating layer 712 with high statistical probability, thereby establishing a low resistance conductive path between the reference layer 711 and the free layer 713. However, when the free layer 713 is magnetized in the direction 733 that is anti-parallel to the direction 731, electrons tunnel across the insulating layer 712 with low statistical probability, thereby establishing a high resistance between the reference layer 711 and the free layer 713. Thus, switching the magnetization direction of the free layer 713 effectively switches the MJT 710 between a conductive state and a substantially non-conductive state.

[0035] As Figure 7 illustrated and described herein according to this embodiment of the application, the device 700 differs significantly from the similar device 400 of FIG. 4 because Figure 7 the switching mechanism includes a common metal planar component 751 that is overlaid by a thin heavy metal layer 701, and because the injected charge current 720 flows substantially through the common metal rather than the heavy metal, thereby substantially replacing the heavy metal with common metal. Whereas the device 400 relies on the spin Hall effect in the heavy metal planar component 401 to generate the spin current 422, the device 700 does not rely on the spin Hall effect, but rather utilizes the orbital Hall effect in the common metal planar component 751, which is then converted to an out-of-plane spin current 722 via the thin heavy metal layer 701.

[0036] A non-limiting application of the device 700 is for data storage, where a single data bit can be represented by the conductive state of the MJT 710.

[0037] The first electrical terminal Tl 702 is connected to the reference layer 711; the second electrical terminal T2 703 is connected to one side of the common metal plane component 751; and the third electrical terminal T3 704 is connected to the other side of the common metal plane component 751. Thus, the magnitude and direction of the in-plane charge flow 720 is controlled by the current flowing between terminal T2 703 and terminal T3 704 (e.g., from a bi-directional power source 731) that changes the direction of the current to selectively write a data bit value of 0 or 1. The conductive state of the MTJ 710 can be externally detected by sensing the conductance between terminal Tl 702 and terminal T2 703 or terminal T3 704 (e.g., by a conductance detector 741 that detects the data bit value). A single bit is written by passing a current pulse in the left or right direction between terminal T2 703 and terminal T3 704 according to the desired bit value to be written; and a single bit is read by determining the conductive state of the MTJ 710 (e.g., by sensing the resistance between terminal Tl 702 and terminal T2 703 or terminal T3 704).

[0038] Note that the assignment of bit values to the conductive state is arbitrary, and the bit value 1 can be logically assigned to the MTJ conductive state or the MTJ non-conductive state. Figure 7 The bit values shown in FIG. 6 are for illustrative purposes only and are not limiting. FIG. 7 shows a cross-sectional view of a memory bit cell 700 that includes a MTJ 710 and a common metal plane component 751. The common metal plane component 751 is a metal plane that is common to the MTJ 710 and the MTJ 720. The common metal plane component 751 is connected to the reference layer 711 of the MTJ 710 and the reference layer 712 of the MTJ 720. The common metal plane component 751 is connected to the MTJ 710 and the MTJ 720 through the reference layers 711 and 712, respectively. The common metal plane component 751 is connected to the MTJ 710 and the MTJ 720 through the reference layers 711 and 712, respectively. The common metal plane component 751 is connected to the MTJ 710 and the MTJ 720 through the reference layers 711 and 712, respectively. The common metal plane component 751 is connected to the MTJ 710 and the MTJ 720 through the reference layers 711 and 712, respectively. The common metal plane component 751 is connected to the MTJ 710 and the MTJ 720 through the reference layers 711 and 712, respectively. The common metal plane component 751 is connected to the MTJ 710 and the MTJ 720 through the reference layers 711 and 712, respectively. The common metal plane component 751 is connected to the MTJ 710 and the MTJ 720 through the reference layers 711 and 712, respectively. The common metal plane component 751 is connected to the MTJ 710 and the MTJ 720 through the reference layers 711 and 712, respectively. The common metal plane component 751 is connected to the MTJ 710

Claims

1. A device for generating spin current, the device comprising: A planar component for generating out-of-plane orbital currents via the orbital Hall effect (OHE) of in-plane charge currents flowing within the planar component. The planar component is essentially made of ordinary metal lacking a 5d electron shell; a heavy metal layer in surface electrical contact with the planar component is used to convert the out-of-plane orbital current into an out-of-plane spin current. The heavy metal has a 5d electron shell; Ferromagnetic components above the heavy metal layer; Two electrical terminals are connected to different sides of the planar component; A resistance measuring device, wherein the resistance measuring device is connected between the two electrical terminals.

2. The device according to claim 1, wherein, The common metal is selected from the group consisting of: copper; and aluminum.

3. The device according to claim 1, wherein, The heavy metal is selected from the group consisting of: platinum; tungsten; and tantalum.

4. The device according to claim 1, wherein, The device is operable to detect and measure an external magnetic field that causes the magnetic field in the ferromagnetic component to rotate.

5. The device according to claim 1, further comprising: The magnetic tunnel junction above the heavy metal layer, wherein the magnetic tunnel junction comprises: Reference layer, and Free layer, and in which The free layer is electrically connected to the heavy metal layer; This enables the magnetic tunnel junction to operate to store a single data bit; A first electrical terminal is connected to the reference layer of the magnetic tunnel junction; A second electrical terminal is connected to one side of the planar component; A third electrical terminal is connected to one side of the planar component; A bidirectional power supply, connected between the second and third electrical terminals, operable to inject in-plane charge current into the planar component to write data bits; and A conductivity detector, connected between the first electrical terminal and one of the second and third electrical terminals, is operable to determine the conductivity state of the magnetic tunnel junction.

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