A quantitative method and system for detecting terahertz signals using a rotating magnetic field.

Abstract

This invention discloses a quantitative method and system for magnetic anisotropy based on terahertz signal detection using a rotating magnetic field. The method includes: (1) acquiring a magnetic / non-magnetic material film to be tested, wherein the magnetic / non-magnetic material film includes at least one non-magnetic thin film layer with strong spin-charge conversion and at least one magnetic thin film layer; (2) emitting a femtosecond laser pump pulse to the magnetic / non-magnetic material film to radiate terahertz waves; (3) applying a magnetic field to the magnetic / non-magnetic material film; (4) setting the relative time delay between the femtosecond laser detection pulse and the femtosecond laser pump pulse to the signal position of the terahertz wave, and continuously rotating the angle of the applied magnetic field to detect the terahertz wave signal under different magnetic field angles using the femtosecond laser detection pulse; (5) calculating the magnetic anisotropy field of the magnetic thin film layer based on the terahertz wave signal under different magnetic field angles. This invention does not require contact with the sample for measurement, nor does it require micro / nano fabrication of the test material. The preparation and testing processes are simple, and non-destructive testing can be achieved.

Description

Technical Field

[0001] This invention relates to quantitative techniques for magnetic anisotropy, and more particularly to a quantitative method and system for magnetic anisotropy based on the detection of terahertz signals using a rotating magnetic field. Background Technology

[0002] Magnetic anisotropy refers to the anisotropy of a magnetic material along different magnetization orientations during magnetization. As a fundamental magnetic property, it is widely used in magnetic memory, magnetic sensors, and related devices. In magnetic memory devices represented by giant magnetoresistance, tunneling magnetoresistance, and spin-transfer torque, antiferromagnetic layers are typically used to induce unidirectional magnetic anisotropy to achieve a "switch" of resistance. Magnetic topological structures, represented by skyrmions, hold promise for efficient information transmission and storage; the generation of their topological magnetic structures is closely related to perpendicular magnetic anisotropy. Two-dimensional van der Waals materials, due to their atomic layer thickness, stand out in high-density information storage. According to the Melmann-Wagner theorem, two-dimensional finite-length Heisenberg models do not produce spontaneous magnetization, and the induced strong magnetic anisotropy can achieve room-temperature magnetism in two-dimensional materials. Therefore, developing quantitative methods for magnetic anisotropy in magnetic systems is crucial for the development of high-density, fast-response, and low-energy-consumption information storage and sensor devices.

[0003] Currently, there are many methods for quantitatively measuring magnetic anisotropy in the field of spintronics, such as the magnetic torque method using magnetic, electrical transport properties and the magneto-optical Kerr effect; and methods using ferromagnetic resonance and Brillouin scattering frequency changes. The magnetic torque method is one of the important methods for measuring magnetic anisotropy. Under the condition of ensuring uniform rotation of the system's single domains, it quantifies the magnitude of magnetic anisotropy by measuring the magnetic properties of the sample through a rotating magnetic field. The latter method quantifies the magnitude of the anisotropic field by measuring the frequency response of a magnetic sample after being excited by microwaves or optical fields, combined with the Landau-Lifshitz-Gilbert equations. The above experimental measurement methods are mainly static or quasi-static experimental measurement methods, and some require contact measurement during the measurement process, or require micro / nano fabrication of the sample before measurement. The preparation process is complex and not conducive to rapid and non-destructive testing of the sample. Summary of the Invention

[0004] To address the problems existing in the prior art, the purpose of this invention is to provide a non-contact, simple, and non-destructive method and system for quantitative magnetic anisotropy based on the detection of terahertz signals using a rotating magnetic field.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A quantitative method for magnetic anisotropy based on the detection of terahertz signals using a rotating magnetic field includes the following steps:

[0007] (1) Obtain a magnetic / non-magnetic material film to be tested, wherein the magnetic material film to be tested includes at least one non-magnetic thin film layer with strong spin-charge conversion and at least one magnetic thin film layer with magnetic anisotropy;

[0008] (2) A femtosecond laser pump pulse is emitted to the magnetic / non-magnetic material film to be tested. The magnetic thin film layer is irradiated by the femtosecond laser pump pulse to generate a spin current, which is injected into the non-magnetic thin film layer. The non-magnetic thin film layer converts the spin current into a transient charge flow on the picosecond time scale, thereby radiating terahertz waves.

[0009] (3) Apply a magnetic field to the magnetic / non-magnetic material film to be tested, wherein the magnetic field plane is perpendicular to the incident direction of the femtosecond laser pump pulse;

[0010] (4) Set the relative time delay between the femtosecond laser probe pulse and the femtosecond laser pump pulse to the signal position of the terahertz wave, and continuously rotate the angle of the applied magnetic field to detect the terahertz wave signal under different magnetic field angles through the femtosecond laser probe pulse.

[0011] (5) The magnetic anisotropy field of the magnetic thin film layer is calculated based on the terahertz wave signal under different magnetic field angles.

[0012] Furthermore, the material of the magnetic thin film layer is any one of the following: magnetic metals Fe, Co, Ni, CoFeB; magnetic oxides Fe2O3, Fe3O4, Cr2O3, NiO, CoO; magnetic alloys Ni2MnGa, Ni2MnIn, Co2MnAl, Co2VGa; two-dimensional magnetic materials CrI3, CrBr3, MnBi2Te4, Fe3GeTe2, CrSBr; and magnetic semiconductor materials (Ga,Mn)As.

[0013] Furthermore, the material of the non-magnetic thin film layer is any one of the following: non-magnetic metals Pt, W, Pd, Ta; interface inversion symmetry breaking Ag / Bi; or topological insulators Bi2Se3 and Bi2Te3.

[0014] Furthermore, a magnetic field generated by an electromagnet, superconducting coil, or permanent magnet is applied to the magnetic / non-magnetic material film to be tested. By changing the current magnitude in the two pairs of orthogonal vector magnet coils, or rotating the direction of the electromagnet or permanent magnet, or rotating the magnetic / non-magnetic material film to be tested, the angle of the applied magnetic field relative to the sample is rotated.

[0015] Furthermore, the femtosecond laser detection pulses detect mutually orthogonal terahertz signals, specifically selecting a set of horizontal components P. x and vertical component P y To conduct detection.

[0016] Furthermore, step (5) specifically includes:

[0017] (5.1) Obtain the horizontal component P of the terahertz wave signal detected by the femtosecond laser probe pulse at different magnetic field angles. x and vertical component P y ;

[0018] (5.2) The horizontal component P under different magnetic field angles x and vertical component P y Vector superposition is performed to obtain the vector form of terahertz wave signals under different magnetic field angles;

[0019] (5.3) Obtain the polarization angle of the terahertz wave under different magnetic field angles. Based on the fact that its electric field polarization angle is always perpendicular to the magnetization angle, obtain the magnetization angle of the magnetic thin film layer under different magnetic field angles:

[0020]

[0021] In the formula, θ M Indicates the magnetization angle of the magnetic thin film layer;

[0022] (5.4) If the magnetic thin film layer has uniaxial magnetocrystalline anisotropy, then substituting into the following equation yields the uniaxial anisotropic field of the magnetic thin film layer:

[0023]

[0024] In the formula, H u H represents the magnitude of the uniaxial magnetic anisotropy field of the magnetic thin film layer, and θ represents the applied magnetic field. H Indicates the angle of the magnetic field;

[0025] If the magnetic thin film layer has four-dimensional magnetocrystalline anisotropy, then substituting into the following equation yields the four-dimensional anisotropic field of the magnetic thin film layer:

[0026]

[0027] In the formula, H4 represents the magnitude of the four-dimensional magnetic anisotropy field of the magnetic thin film layer.

[0028] A quantitative magnetic anisotropy system based on the detection of terahertz signals using a rotating magnetic field includes:

[0029] The magnetic / non-magnetic material film to be tested includes at least one non-magnetic thin film layer with strong spin-charge conversion and at least one magnetic thin film layer with magnetic anisotropy.

[0030] A magnetic field application module is used to apply a magnetic field to the magnetic / non-magnetic material film to be tested, wherein the magnetic field plane is perpendicular to the incident direction of the femtosecond laser pump pulse.

[0031] The magnetic field rotation module is used to continuously rotate the angle of the applied magnetic field to obtain a rotating magnetic field. The module achieves rotation of the applied magnetic field relative to the sample by changing the current magnitude in two pairs of orthogonal vector magnet coils, rotating the direction of the electromagnet or permanent magnet, or rotating the magnetic / non-magnetic material film under test.

[0032] The femtosecond laser pump-detection module is used to emit femtosecond laser pump pulses to the magnetic / non-magnetic material film under test. The magnetic thin film layer is irradiated by the femtosecond laser pump pulse to generate a spin current, which is then injected into the non-magnetic thin film layer. The non-magnetic thin film layer converts the spin current into a transient charge flow on the picosecond timescale, thereby radiating terahertz waves.

[0033] The magnetic anisotropy field calculation module is used to calculate the magnetic anisotropy field of the magnetic thin film layer based on the terahertz wave signal under different magnetic field angles.

[0034] Furthermore, the magnetic anisotropic field calculation module specifically includes:

[0035] The data acquisition unit is used to acquire the horizontal component P of the terahertz wave signal at different magnetic field angles detected by the femtosecond laser probe pulse. x and vertical component P y ;

[0036] Vector superposition unit is used to combine the horizontal component P under different magnetic field angles. x and vertical component P y Vector superposition is performed to obtain the vector form of terahertz wave signals under different magnetic field angles;

[0037] The magnetization angle calculation unit is used to obtain the polarization angle of the terahertz electric field under different magnetic field angles. Based on the fact that the electric field polarization angle and the magnetization angle are always perpendicular, the magnetization angle of the magnetic thin film layer under different magnetic field angles is obtained.

[0038]

[0039] In the formula, θ M Indicates the magnetization angle of the magnetic thin film layer;

[0040] Anisotropic field calculation unit, used to obtain the uniaxial anisotropic field of the magnetic thin film layer by substituting into the following formula if the magnetic thin film layer has uniaxial magnetocrystalline anisotropy:

[0041]

[0042] In the formula, H u H represents the magnitude of the uniaxial magnetic anisotropy field of the magnetic thin film layer, and θ represents the applied magnetic field. H Indicates the angle of the magnetic field;

[0043] If the material of the magnetic thin film layer has four-dimensional magnetocrystalline anisotropy, then substituting into the following equation yields the four-dimensional anisotropic field of the magnetic thin film layer:

[0044]

[0045] In the formula, H4 represents the magnitude of the four-dimensional magnetic anisotropy field of the magnetic thin film layer.

[0046] Compared with the prior art, the advantages of this invention are: it has the advantages of non-contact measurement and no need for micro-nano processing, and the sample preparation process is simple, which is conducive to rapid and non-destructive testing of samples. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the method for quantitatively detecting terahertz signals by rotating magnetic fields in this invention;

[0048] Figure 2 The Co / Pt / MgO(110) sample in this invention is along the difficult axis And Easy Axis H x / / Orthogonal terahertz time-domain spectral information of two crystals of MgO

[001] measured downwards;

[0049] Figure 3 This is a schematic diagram of the two-dimensional terahertz time-domain electric field of the Co / Pt / MgO(110) sample under different magnetic field angles in this invention;

[0050] Figure 4 For the Co / Pt / MgO(110) sample along MgO

[001] and Dependence of orthogonal terahertz peak electric and magnetic fields measured downwards from two crystals;

[0051] Figure 5 The graph shows the relationship between the two orthogonal terahertz peak electric fields of Co / Pt / MgO(110) samples measured under different magnetic field strengths and the magnetic field angle.

[0052] Figure 6 The dependence of magnetic field angle and magnetization angle on Co / Pt / MgO(110) samples under different magnetic fields;

[0053] Figure 7 This is a graph showing the relationship between the ratio of external magnetic field to uniaxial anisotropy and the magnitude of external magnetic field. Detailed Implementation

[0054] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0055] Example 1

[0056] Embodiment 1 of the present invention provides a method for quantitative analysis of magnetic anisotropy based on the detection of terahertz signals using a rotating magnetic field, such as... Figure 1 and Figure 2 As shown, it includes the following steps:

[0057] (1) Obtain a magnetic / non-magnetic material film to be tested, wherein the magnetic / non-magnetic material film to be tested includes at least one non-magnetic thin film layer with strong spin-charge conversion and at least one magnetic thin film layer with magnetic anisotropy.

[0058] The magnetic thin film layer is made of any one of the following materials: magnetic metals Fe, Co, Ni, CoFeB; magnetic oxides Fe2O3, Fe3O4, Cr2O3, NiO, CoO; magnetic alloys Ni2MnGa, Ni2MnIn, Co2MnAl, Co2VGa; two-dimensional magnetic materials CrI3, CrBr3, MnBi2Te4, Fe3GeTe2, CrSBr; and magnetic semiconductor materials (Ga,Mn)As. The non-magnetic thin film layer is made of a material with strong spin-orbit coupling, specifically any one of the following: non-magnetic metals Pt, W, Pd, Ta; interface inversion symmetry breaking Ag / Bi; and topological insulators Bi2Se3 and Bi2Te3. This material can convert spin current into charge current through the inverse spin Hall effect or the Rashba-Edelstein effect, thereby radiating terahertz waves.

[0059] (2) A femtosecond laser pump pulse is emitted to the magnetic / non-magnetic material film to be tested. The magnetic thin film layer is irradiated by the femtosecond laser pump pulse to generate a spin current, which is injected into the non-magnetic thin film layer. The non-magnetic thin film layer converts the spin current into a transient charge flow on the picosecond time scale, thereby radiating terahertz waves.

[0060] (3) Apply a magnetic field to the magnetic / non-magnetic material film to be tested, wherein the magnetic field plane is perpendicular to the incident direction of the femtosecond laser pump pulse.

[0061] The process involves applying a magnetic field to the magnetic / non-magnetic material film under test using an electromagnet, superconducting coil, or permanent magnet. The angle of the applied magnetic field relative to the sample is rotated by changing the current in two pairs of orthogonal vector magnet coils, rotating the electromagnet or permanent magnet, or rotating the magnetic material film under test. The magnitude of the applied magnetic field must not be significantly greater or less than the magnitude of the anisotropic field.

[0062] (4) Set the relative time delay between the femtosecond laser probe pulse and the femtosecond laser pump pulse to the signal position of the terahertz wave, and continuously rotate the angle of the applied magnetic field to detect the terahertz wave signal under different magnetic field angles through the femtosecond laser probe pulse.

[0063] In this process, femtosecond laser detection pulses are used to detect terahertz waves in mutually orthogonal directions of the magnetic material film under test. Typically, a set of horizontal components P is selected. x and vertical component P y To conduct detection.

[0064] (5) The magnetic anisotropy field of the magnetic thin film layer is calculated based on the polarization angle of the terahertz wave signal under different magnetic field angles.

[0065] Step (5) specifically includes:

[0066] (5.1) Obtain the horizontal component P of the terahertz wave signal detected by the femtosecond laser probe pulse at different magnetic field angles. x and vertical component P y ;

[0067] (5.2) The horizontal component P under different magnetic field angles x and vertical component P y Vector superposition is performed to obtain the vector form of terahertz wave signals under different magnetic field angles;

[0068] (5.3) Obtain the polarization angle of the terahertz wave under different magnetic field angles. Based on the fact that its electric field strength and magnetization angle are always perpendicular, obtain the magnetization angle of the magnetic thin film layer under different magnetic field angles:

[0069]

[0070] In the formula, θ M Indicates the magnetization angle of the magnetic thin film layer;

[0071] (5.4) If the magnetic thin film layer has uniaxial magnetocrystalline anisotropy, then substituting into the following equation yields the uniaxial anisotropic field of the magnetic thin film layer:

[0072]

[0073] In the formula, H represents the magnitude of the uniaxial magnetic anisotropy field of the magnetic thin film layer, and θ represents the applied magnetic field. H θ represents the angle of the magnetic field. M The magnetization angle of the magnetic thin film layer is represented by K, M represents the magnetization intensity of the sample, and K represents the magnetization intensity of the sample. u This represents the uniaxial magnetic anisotropy constant of the sample.

[0074] If the magnetic thin film layer has four-dimensional magnetocrystalline anisotropy, then substituting into the following equation yields the four-dimensional anisotropic field of the magnetic thin film layer:

[0075]

[0076] In the formula, K represents the magnitude of the four-dimensional magnetic anisotropy field of the magnetic thin film layer, and K4 represents the four-dimensional magnetic anisotropy constant of the sample.

[0077] The working principle of this invention is as follows: When a rotating external bias magnetic field is applied, the direction of the effective field generated under the combined action of the anisotropic field and the external magnetic field is not always parallel to the direction of the external magnetic field. By obtaining the relationship between the terahertz signal and the direction of the external magnetic field, the dependence of the effective field on the external magnetic field can be obtained, thereby quantifying the magnitude of the anisotropic field, as detailed below:

[0078] (1) Relationship between terahertz waves and sample magnetization direction:

[0079] Femtosecond laser pump pulses irradiate magnetic materials, generating a spin-polarized charge flow that transfers its spin angular momentum to the adjacent non-magnetic material. Due to the inverse spin Hall effect or the Rashba-Edelstein effect, this is converted into a transient charge flow on the picosecond timescale, which radiates terahertz waves. According to the inverse spin Hall effect conversion rule E... THz ∝γj s ×σ, or the Rashba-Edelstein effect transformation rule E THz ∝λj s ×z, here E THz The electric field vector of the terahertz wave is represented by γ, the spin Hall angle of the non-magnetic material layer is represented by M, and the magnetization is represented by j. s Let σ represent the spin current, σ represent the spin direction, and z represent the potential gradient direction perpendicular to the interface. Since the polarization direction of the generated terahertz wave is always perpendicular to both the spin direction and the interface potential gradient direction, the magnetization direction of the magnetic thin film layer can be obtained by vector synthesis of the polarization direction of the terahertz wave.

[0080] (2) Principle of the method for quantitatively detecting the magnitude of magnetic anisotropic fields using rotating magnetic fields to detect terahertz waves:

[0081] Consider a single-domain uniform rotation system, in which the magnetization direction of the material is determined by the combined action of the anisotropic field and the Zeeman field.

[0082] For a uniaxial magnetocrystalline anisotropic system, its energy can be described as follows:

[0083] E=K u sin 2 θ M -HMcos(θ H -θ M (1)

[0084] In the formula, E represents the total energy, and K u θ represents the uniaxial magnetocrystalline anisotropy constant of the magnetic thin film layer. M θ represents the magnetization angle of the magnetic thin film layer, H represents the magnetization intensity, H represents the external magnetic field, and θ represents the magnetization angle of the magnetic thin film layer.H It represents the magnetic field strength.

[0085] For ferromagnetic systems, since the precession timescale is much larger than the sub-picosecond order of magnitude, we can approximate that the total energy of the system does not evolve with sub-picosecond time. We assume the magnetic system is in equilibrium:

[0086]

[0087] And thus obtain

[0088]

[0089] In the formula, H u For a uniaxial anisotropic field, H u =2K u / M.

[0090] For a four-dimensional anisotropic system, its energy can be described as:

[0091] E = K4sin 2 θ M cos 2 θ M -HMcos(θ H -θ M (4)

[0092] In the formula, K4 represents the four-degree magnetic anisotropy constant of the magnetic thin film layer.

[0093] Similarly, considering the magnetic system in equilibrium, we can obtain:

[0094]

[0095] In the formula, H4 is a four-dimensional anisotropic field, H4=K4 / M.

[0096] Therefore, by fixing the pump-probe time to the position of the terahertz wave signal and rotating the magnetic field angle, the vector terahertz electric field under different magnetic field angles is measured to obtain the polarization direction of the terahertz wave, and then the dependence of the magnetic field angle on the magnetization angle is obtained. Based on this dependence and formula (3) or (5), the magnitude of the anisotropic field can be obtained.

[0097] Example 2

[0098] Embodiment 2 of the present invention provides a quantitative magnetic anisotropy system based on a rotating magnetic field to detect terahertz signals, used to execute the method described in Embodiment 1, comprising:

[0099] The magnetic / non-magnetic material film to be tested includes at least one non-magnetic thin film layer with strong spin-charge conversion and at least one magnetic thin film layer with magnetic anisotropy.

[0100] A magnetic field application module is used to apply a magnetic field to the magnetic / non-magnetic material film to be tested, wherein the magnetic field plane is perpendicular to the incident direction of the femtosecond laser pump pulse.

[0101] The magnetic field rotation module is used to continuously rotate the angle at which the applied magnetic field is applied to obtain a rotating magnetic field. The magnetic field application module applies a magnetic field to the location of the magnetic / non-magnetic material film to be tested using an electromagnet, a superconducting coil, or a permanent magnet. The magnetic field rotation module achieves the rotation of the applied magnetic field relative to the sample by changing the current magnitude in two pairs of orthogonal vector magnet coils, rotating the direction of the electromagnet or permanent magnet, or rotating the magnetic / non-magnetic material film to be tested.

[0102] The femtosecond laser pump-probe module is used to emit femtosecond laser pump pulses onto the magnetic / non-magnetic material film under test. The femtosecond laser used is compatible with femtosecond laser oscillators and femtosecond laser amplifiers; the terahertz electric field signal is acquired through electro-optic sampling and balanced detection, while the terahertz electric field signal at different times is obtained through pump-probe technology. A magnetic field is applied along a certain in-plane direction of the magnetic material, and a spin current is generated by irradiating the magnetic thin film layer with a femtosecond laser pump pulse. This spin current is then injected into the non-magnetic thin film layer, which converts the spin current into a transient charge flow on a picosecond timescale, thereby radiating terahertz waves. By rotating the magnetic field angle, the terahertz wave signal at different magnetic field angles is detected by a femtosecond laser probe pulse.

[0103] The magnetic anisotropy field calculation module is used to calculate the magnetic anisotropy field of the magnetic thin film layer based on the terahertz wave signal under different magnetic field angles.

[0104] Specifically, the magnetic anisotropic field calculation module includes:

[0105] The data acquisition unit is used to acquire the horizontal component P of the terahertz wave signal at different magnetic field angles detected by the femtosecond laser probe pulse. x and vertical component P y ;

[0106] Vector superposition unit is used to combine the horizontal component P under different magnetic field angles. x and vertical component P y Vector superposition is performed to obtain the vector form of terahertz wave signals under different magnetic field angles;

[0107] The magnetization angle calculation unit is used to obtain the polarization angle of the terahertz electric field under different magnetic field angles. Based on the fact that the electric field polarization angle and the magnetization angle are always perpendicular, the magnetization angle of the magnetic thin film layer under different magnetic field angles is obtained.

[0108]

[0109] In the formula, θ M Indicates the magnetization angle of the magnetic thin film layer;

[0110] Anisotropic field calculation unit, used to obtain the uniaxial anisotropic field of the magnetic thin film layer by substituting into the following formula if the magnetic thin film layer has uniaxial magnetocrystalline anisotropy:

[0111]

[0112] In the formula, H u H represents the magnitude of the uniaxial magnetic anisotropy field of the magnetic thin film layer, and θ represents the applied magnetic field. H Indicates the angle of the magnetic field;

[0113] If the magnetic thin film layer has four-dimensional magnetocrystalline anisotropy, then substituting into the following equation yields the four-dimensional anisotropic field of the magnetic thin film layer:

[0114]

[0115] In the formula, H4 represents the magnitude of the four-dimensional magnetic anisotropy field of the magnetic thin film layer.

[0116] The system provided in Embodiment 2 of the present invention can be used to execute the method provided in Embodiment 1 of the present invention, and has the corresponding functions and beneficial effects of executing the method.

[0117] It is worth noting that in the embodiments of the above-mentioned determining device, the various units and modules included are only divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be achieved; in addition, the specific names of each functional unit are only for easy differentiation and are not used to limit the scope of protection of the present invention.

[0118] The embodiments described above are merely illustrative. The modules described as separate components may or may not be physically separate, and the components shown as modules may or may not be physical modules; that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art will clearly understand that each implementation can be achieved using software plus necessary general-purpose hardware platforms, or it can be implemented solely through hardware, as long as the function or purpose can be achieved.

[0119] The present invention will now be experimentally verified.

[0120] Figure 1This is a schematic diagram of the experimental setup. The femtosecond laser pulses generated by the laser emitter used in the experiment have a wavelength of 800 nm and a pulse width of 35 fs. By constructing a pump-probe terahertz time-domain spectral optical path, the pulsed laser is divided into a pump laser and a probe laser. The sample (the magnetic / non-magnetic heterojunction to be tested) is a Co / Pt bilayer film grown on an MgO(110) substrate, where Co is the magnetic layer and Pt is the non-magnetic layer. After the pump light excites the sample to emit terahertz signals, the detection directions are fixed along the horizontal (easy axis of the sample) and vertical (difficult axis of the sample) directions, respectively, and the time delay is fixed at the terahertz peak position. By continuously rotating the in-plane magnetic field angle perpendicular to the incident direction of the pump light, the terahertz peak signals along the easy and difficult axes of the sample are obtained. Then, the magnitude of the anisotropic field is quantified by the relationship between the signal and the angle of the applied magnetic field.

[0121] Figure 2 Magnetic fields (H0) were applied to the Co / Pt / MgO(110) sample in both the difficult and easy axes. y H x ), along difficult and easy axes detection (P) y P x The terahertz electric field signal was obtained by changing the time delay between the pump light and the probe light. For the Co / Pt / MgO(110) sample, the terahertz signal (H) when the magnetic field is along the hard axis and the probe direction is along the hard axis was obtained. y P y ) and the terahertz signal (H) when the magnetic field is along the easy axis and the detection direction is along the difficult axis. x P y The results are basically the same; however, when the magnetic field is along the difficult axis and the probe is along the easy axis (H) y P x This resulted in a smaller terahertz component. This difference in the terahertz signal is precisely due to the contribution of the sample's magnetocrystalline anisotropy.

[0122] Figure 3 This represents the time-domain signal of the terahertz vector electric field measured at several characteristic magnetic field angles. Magnetic field angle θ H Defined as the angle between the applied magnetic field and the easy axis of the sample. When the applied magnetic field is along the easy axis of the sample, the generated terahertz polarization direction is along the difficult axis of the sample; when θ H At θ = 60° and 240°, the generated terahertz polarization direction deviates from the hard axis by about 12°; when θ = 0°... H At 120° and 300°, the generated terahertz polarization direction deviates from the hard axis by approximately -12°. At several characteristic magnetic field angles, the generated terahertz polarization direction is essentially located near the hard axis.

[0123] Figure 4 Shown in H y P x H y Py H x P x and H x P y The relationship between the peak electric field of terahertz and the magnetic field under four configurations. When the applied magnetic field is along the easy axis, the terahertz signal is emitted along the difficult axis, and the peak terahertz signal exhibits a square loop relationship with the magnetic field. When the applied magnetic field is along the difficult axis, the signal measured along the easy axis tends to increase with the magnetic field, and the detection along the difficult axis shows an inclined square loop.

[0124] Figure 5 The relationship between the peak electric field of terahertz signals measured along the difficult axis and the easy axis under three sets of applied magnetic fields is shown. When probing terahertz signals along the difficult axis, the peak electric field exhibits a step-like trend with the change of magnetic field angle; when probing terahertz signals along the easy axis, the peak electric field exhibits a triangular trend with the change of magnetic field angle. When θ H When the magnetic field is near 90° and 270°, the signal component along the easy axis increases, while the signal component along the difficult axis decreases. When the magnetic field is at a certain angle, the magnetization angle θ can be determined by the magnitude of the signals along the difficult and easy axes. M =arctan(P y / P x This allows us to obtain the magnetic field angle θ under different magnetic fields. H With magnetization angle θ M Dependencies, such as Figure 6 As shown.

[0125] By considering the dependence of the magnetic anisotropic field on the magnetization angle, magnetic field angle and magnetic field in formula (3), the magnitude of the uniaxial anisotropic field can be quantified. Figure 7 Showing 2H / H k The dependence on H yielded a Co / Pt / Mg(110) uniaxial anisotropic field size of 4.4 ± 0.1 kOe.

[0126] It should be understood that the embodiments and descriptions above are only the principles, main features and advantages of the present invention. Various changes and modifications can be made to the present invention without departing from the spirit and scope of the invention, and all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A quantitative method for magnetic anisotropy based on the detection of terahertz signals using a rotating magnetic field, characterized in that, Includes the following steps: (1) Obtain a magnetic / non-magnetic material film to be tested, wherein the magnetic / non-magnetic material film to be tested includes at least one non-magnetic thin film layer with strong spin-charge conversion and at least one magnetic thin film layer with magnetic anisotropy; (2) A femtosecond laser pump pulse is emitted to the magnetic / non-magnetic material film to be tested. The magnetic thin film layer is irradiated by the femtosecond laser pump pulse to generate a spin current, which is injected into the non-magnetic thin film layer. The non-magnetic thin film layer converts the spin current into a transient charge flow on the picosecond time scale, thereby radiating terahertz waves. (3) Apply a magnetic field to the magnetic / non-magnetic material film to be tested, with the magnetic field plane perpendicular to the incident direction of the femtosecond laser pump pulse; (4) Set the relative time delay between the femtosecond laser probe pulse and the femtosecond laser pump pulse to the signal position of the terahertz wave, and continuously rotate the angle of the applied magnetic field to detect the terahertz wave signal under different magnetic field angles through the femtosecond laser probe pulse. (5) The magnetic anisotropy field of the magnetic thin film layer is calculated based on the terahertz wave signal under different magnetic field angles; Step (5) specifically includes: (5.1) Obtain the horizontal component of the terahertz wave signal detected by the femtosecond laser probe pulse at different magnetic field angles. and vertical components ; (5.2) Horizontal components under different magnetic field angles and vertical components Vector superposition is performed to obtain the vector form of terahertz wave signals under different magnetic field angles; (5.3) Obtain the polarization angle of the terahertz wave under different magnetic field angles. Based on the fact that its electric field polarization angle is always perpendicular to the magnetization angle, obtain the magnetization angle of the magnetic thin film layer under different magnetic field angles: ， In the formula, Indicates the magnetization angle of the magnetic thin film layer; (5.4) If the magnetic thin film layer has uniaxial magnetocrystalline anisotropy, then substituting into the following equation yields the uniaxial anisotropic field of the magnetic thin film layer: ， In the formula, This represents the magnitude of the uniaxial magnetic anisotropy field of the magnetic thin film layer. Indicates an external magnetic field. Indicates the angle of the magnetic field; If the magnetic thin film layer has four-dimensional magnetocrystalline anisotropy, then substituting into the following equation yields the four-dimensional anisotropic field of the magnetic thin film layer: ， In the formula, This indicates the magnitude of the four-dimensional magnetic anisotropy field of the magnetic thin film layer.

2. The method for quantitative analysis of magnetic anisotropy based on terahertz signals detected by rotating magnetic fields according to claim 1, characterized in that: The material of the magnetic thin film layer is any one of the following: magnetic metals Fe, Co, Ni, CoFeB; magnetic oxides Fe2O3, Fe3O4, Cr2O3, NiO, CoO; magnetic alloys Ni2MnGa, Ni2MnIn, Co2MnAl, Co2VGa; two-dimensional magnetic materials CrI3, CrBr3, MnBi2Te4, Fe3GeTe2, CrSBr; and magnetic semiconductor material (Ga,Mn)As.

3. The quantitative method for magnetic anisotropy based on terahertz signal detection using a rotating magnetic field according to claim 1, characterized in that: The material of the non-magnetic thin film layer is any one of the following: non-magnetic metals Pt, W, Pd, Ta; interface inversion symmetry broken Ag / Bi; or topological insulators Bi2Se3 and Bi2Te3.

4. The method for quantitatively detecting terahertz signals based on a rotating magnetic field according to claim 1, characterized in that: A magnetic field is applied to the magnetic / non-magnetic material film to be tested. The magnetic field is applied at the location of the magnetic / non-magnetic material film to be tested by means of an electromagnet, a superconducting coil or a permanent magnet.

5. The method for quantitatively detecting terahertz signals based on a rotating magnetic field according to claim 1, characterized in that: A magnetic field generated by an electromagnet, superconducting coil, or permanent magnet is applied to the magnetic / non-magnetic material film to be tested. The angle of the applied magnetic field relative to the sample is rotated by changing the current in two pairs of orthogonal vector magnet coils, rotating the direction of the electromagnet or permanent magnet, or rotating the magnetic / non-magnetic material film to be tested.

6. The method for quantitatively detecting terahertz signals based on a rotating magnetic field according to claim 1, characterized in that: The femtosecond laser detection pulses detect mutually orthogonal terahertz signals, specifically selecting a set of horizontal components. and vertical components To conduct detection.

7. A quantitative system for detecting terahertz signals based on a rotating magnetic field, characterized in that, include: The magnetic / non-magnetic material film to be tested includes at least one non-magnetic thin film layer with strong spin-charge conversion and at least one magnetic thin film layer with magnetic anisotropy. The magnetic field application module is used to apply a magnetic field to the magnetic / non-magnetic material film under test. The magnetic field plane is perpendicular to the incident direction of the femtosecond laser pump pulse. The magnetic field rotation module is used to continuously rotate the angle at which the applied magnetic field is applied to obtain a rotating magnetic field. Femtosecond laser pump-probe module, used to emit femtosecond laser pump pulses to the magnetic / non-magnetic material film under test; Spin currents are generated by irradiating a magnetic thin film layer with a femtosecond laser pump pulse and then injected into a non-magnetic thin film layer. The non-magnetic thin film layer converts the spin currents into transient charge flows on a picosecond timescale, thereby radiating terahertz waves. The magnetic anisotropy field calculation module is used to calculate the magnetic anisotropy field of the magnetic thin film layer based on the terahertz wave signal under different magnetic field angles. The magnetic anisotropic field calculation module specifically includes: The data acquisition unit is used to acquire the horizontal components of the terahertz wave signal at different magnetic field angles detected by the femtosecond laser probe pulse. and vertical components ; Vector superposition unit is used to combine the horizontal components under different magnetic field angles. and vertical components Vector superposition is performed to obtain the vector form of terahertz wave signals under different magnetic field angles; The magnetization angle calculation unit is used to obtain the polarization angle of the terahertz electric field under different magnetic field angles. Based on the fact that the electric field polarization angle and the magnetization angle are always perpendicular, the magnetization angle of the magnetic thin film layer under different magnetic field angles is obtained. ， In the formula, Indicates the magnetization angle of the magnetic thin film layer; Anisotropic field calculation unit, used to obtain the uniaxial anisotropic field of the magnetic thin film layer by substituting into the following formula if the magnetic thin film layer has uniaxial magnetocrystalline anisotropy: ， In the formula, This represents the magnitude of the uniaxial magnetic anisotropy field of the magnetic thin film layer. Indicates an external magnetic field. Indicates the angle of the magnetic field; If the material of the magnetic thin film layer has four-dimensional magnetocrystalline anisotropy, then substituting into the following equation yields the four-dimensional anisotropic field of the magnetic thin film layer: ， In the formula, This indicates the magnitude of the four-dimensional magnetic anisotropy field of the magnetic thin film layer.

8. A quantitative system for detecting terahertz signals based on a rotating magnetic field, as described in claim 7, characterized in that: The magnetic field rotation module achieves angular rotation of the applied magnetic field relative to the sample by changing the current magnitude in two pairs of orthogonal vector magnet coils, rotating the direction of the electromagnet or permanent magnet, or rotating the magnetic / non-magnetic material film to be tested.

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