A device for flipping magnetic moment without magnetic field assistance using vertical spin polarized spin current and its preparation method

Abstract

The present invention discloses a device for flipping magnetic moment with a spin current of vertical spin polarization without the assistance of magnetic field and a preparation method thereof. The device comprises a substrate, a strong spin-orbit coupling layer and a magnetization layer from bottom to top; the strong spin-orbit coupling layer comprises at least one of the following materials: a heavy metal material, a topological insulator material, an antiferromagnetic material with both sublattice center inversion symmetry breaking and global center inversion symmetry; the magnetization layer comprises a material with vertical easy magnetization and / or a material with an in-plane easy magnetization axis. The preparation method thereof comprises the following steps: depositing a strong spin-orbit coupling layer and a magnetization layer on a substrate in sequence. The conventional spin current parallel to the spin polarization direction of the device of the present invention enables the device with vertical easy magnetization and easy magnetization along the in-plane x direction to realize a 180° flip of the magnetic moment without the assistance of magnetic field, and the size of the spin current of vertical spin polarization can be regulated by changing the direction of the antiferromagnetic magnetic moment of the strong spin-orbit coupling layer.

Description

Technical Field

[0001] The invention relates to a device for using a vertical spin polarized spin current to assist in flipping magnetic moment without a magnetic field and a preparation method thereof, belonging to the field of electronic information materials. Background Art

[0002] Using spin-orbit torque to flip the magnetic moment and read out the high and low resistance states through the magnetoresistance effect is an important way to achieve information storage. Since the phenomenon was discovered in Pt / Co / AlOx and CoFeB / Ta systems in 2011, it has aroused widespread research interest. Unlike the traditional spin transfer torque mechanism in which a spin-polarized current passes through a magnetic layer to flip the magnetic moment of the magnetic layer, the spin-orbit torque mechanism relies on the strong spin-orbit coupling in heavy metals to realize spin flow instead of current injection into the magnetic layer device. At the same time, it shows rich physical phenomena and potential application value, which is conducive to improving device tolerance and reducing the current density of magnetization reversal, opening up a new branch of spin electronics research. So far, the research on spin-orbit torque is to apply current along the in-plane x direction in heavy metals or topological insulators, and generate spin polarization (σy) along the y direction and spin current flowing in the out-of-plane z direction based on the spin Hall effect or the interface Rashba effect (the three satisfy the cross-product relationship). The spin polarization in the y direction can provide a strong anti-damping torque effect to the magnetic layer with the easy axis along the y direction, thereby realizing the magnetization reversal of the adjacent magnetic layer. However, the device designed by the above method is not suitable for high-density storage that requires perpendicular easy magnetization. The current spin current with spin polarization along the in-plane y direction requires external magnetic field assistance in the process of reversing the perpendicular easy magnetization and the in-plane x direction easy magnetization of magnetic materials. Therefore, a device that can achieve efficient magnetization reversal without auxiliary field is urgently needed. Summary of the invention

[0003] The object of the present invention is to provide a device for switching magnetic moment without the assistance of magnetic field by using vertical spin polarized spin current and a preparation method thereof.

[0004] The present invention provides a device that uses a vertically spin-polarized spin current to flip the magnetic moment without the assistance of a magnetic field. The device comprises, from bottom to top, a substrate, a strong spin-orbit coupling layer and a magnetization layer.

[0005] The strong spin-orbit coupling layer is made of at least one of the following materials: a heavy metal material, a topological insulator material, an antiferromagnetic material having both sublattice center inversion symmetry breaking and global center inversion symmetry;

[0006] The magnetic layer includes a material having a perpendicular easy magnetization axis and / or a material having an in-plane easy magnetization axis.

[0007] In the above device, the substrate is a substrate with high crystal asymmetry;

[0008] The type of crystal substrate with high crystal asymmetry is selected from at least one of MgO (110), MgO (111) and PMN-PT (011) (Chinese name is magnesium niobate lead titanate crystal substrate).

[0009] In the above device, the heavy metal material includes Pt and / or Ta;

[0010] The topological insulator material includes Bi2Se3 and / or Bi2Te3;

[0011] The antiferromagnetic materials having both sublattice center inversion symmetry breaking and global center inversion symmetry include Mn2Au and / CuMnAs.

[0012] In the above device, the material having perpendicular easy magnetization includes at least one of CoFeB, Co / Ni multilayer film and Co / Pt multilayer film;

[0013] The material having an in-plane easy magnetization axis includes at least one of NiFe, Co and Fe.

[0014] The present invention also provides a method for preparing the above-mentioned device that uses a vertically spin-polarized spin current to assist in flipping the magnetic moment without a magnetic field, comprising the following steps: depositing the strong spin-orbit coupling layer and the magnetization layer on the substrate in sequence, thereby obtaining the device that uses a vertically spin-polarized spin current to assist in flipping the magnetic moment without a magnetic field.

[0015] In the above-mentioned preparation method, the strong spin-orbit coupling layer and the magnetization layer are deposited by magnetron sputtering.

[0016] In the above-mentioned preparation method, the device for using a vertically spin-polarized spin current to flip the magnetic moment without the assistance of a magnetic field also includes a device processed into a cross-shaped center by ultraviolet exposure, development, and argon ion etching; specifically, the size of the cross-shaped center is 5×5μm 2 ;

[0017] A wire is led out from each of the four ports of the device to test the magnetic resistance, a current is passed through a path of the cross, and the Hall resistance is measured at two ends perpendicular to the cross.

[0018] The device of the present invention that uses a vertically spin-polarized spin current to flip the magnetic moment without the assistance of a magnetic field is applied to the preparation of a high-density, low-power information storage device.

[0019] The present invention has the following advantages:

[0020] The present invention utilizes a substrate with a high crystal asymmetry and a vertical spin polarization spin current generated by a strong spin-orbit coupling layer to prepare a device for flipping magnetic moments without the assistance of a magnetic field. The vertical spin polarization spin current provides an effective field to replace the external magnetic field. Conventional spin currents parallel to the spin polarization direction enable devices with vertical easy magnetization and easy magnetization along the in-plane x direction to achieve 180-degree flipping of magnetic moments without the assistance of a magnetic field. The size of the vertical spin polarization spin current can be regulated by changing the direction of the antiferromagnetic magnetic moment of the strong spin-orbit coupling layer, thereby regulating the difficulty of flipping the vertical easy magnetization layer without the assistance of a magnetic field. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a graph showing the Hall resistance change results corresponding to the magnetic moment reversal without magnetic field assistance of the MgO(111) / Co(0.4nm) / Pd(0.8nm) / Co(0.4nm) / Pd(2nm) structure in Example 1 of the present invention.

[0022] Figure 2 This is a graph of the Hall resistance change results corresponding to a positive 1000Oe auxiliary magnetic field and a negative 1000Oe auxiliary magnetic field for the MgO(111) / Co(0.4nm) / Pd(0.8nm) / Co(0.4nm) / Pd(2nm) structure in Example 1 of the present invention.

[0023] Figure 3 This is the result of the magneto-optical Kerr microscope test of the PMN-PT (011) / Mn2Au (12nm) / NiFe (16nm) heterostructure at room temperature in Example 2 of the present invention. The central rectangular area is the magnetic layer. When the current density is 1.43×10 7 A cm -2 When the magnetic field is turned on, all the in-plane magnetic moments flip 180 degrees, and the image contrast completely changes from dark to light. DETAILED DESCRIPTION

[0024] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0025] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0026] Example 1: A heterostructure of MgO (111) / Co (0.4 nm) / Pd (0.8 nm) / Co (0.4 nm) / Pd (2 nm) was prepared for flipping the perpendicular magnetic moment.

[0027] A Co(0.4nm) / Pd(0.8nm) / Co(0.4nm) / Pd(2nm) multilayer film structure was deposited on a MgO(111) substrate by magnetron sputtering.

[0028] Co and Pd were sputtered at room temperature. The background vacuum before sputtering was 1×10 -8 Torr, and the DC sputtering power is 20W.

[0029] Then, the multilayer film was processed into a center size of 5×5μm by UV exposure and argon ion etching. 2 A cross-shaped device is used, and a wire is drawn from each of the four ports of the cross device to test the magnetic resistance. A current is passed through one path of the cross, and the Hall resistance is measured at the two ends perpendicular to it.

[0030] Depend on Figure 1-2 The results of the PPMS (Physical Performance Testing System) magnetoresistance test at room temperature (25°C) show that when the external magnetic field is zero, the current pulse increases from 1.6×10 8 A cm -2 to -1.6×10 8 A cm -2 Then to 1.6×10 8 A cm -2 The resistance change obtained by the test is high resistance (1.6×10 8 A cm -2 )→Low resistance (-1.6×10 8 A cm -2 )→High impedance (1.6×10 8 A cm -2 ). This phenomenon occurs mainly because the current drives the magnetic moment reversal of the Co / Pd multilayer film, causing a significant change in the measured Hall resistance. The device of the present invention uses a multifunctional physical property measurement system (PPMS) to measure the degree of magnetoresistance change at room temperature (25°C) to be 50% of that when an auxiliary magnetic field of 100mT is applied.

[0031] Example 2: Preparation of PMN-PT (011) / Mn2Au (12nm) / NiFe (16nm) structure heterostructure for flipping the in-plane magnetic moment

[0032] A Mn2Au (12nm) / NiFe (16nm) multilayer film structure was deposited on a PMN-PT (011) substrate by magnetron sputtering, in which the thickness of Mn2Au was 12nm and the thickness of NiFe was 16nm.

[0033] The background vacuum is 2×10 5 Pa, sputtered Mn2Au at a high temperature of 300℃ with a sputtering power of 30W, then cooled to room temperature and sputtered NiFe with a sputtering power of 10W.

[0034] The prepared Mn2Au was epitaxially grown on the substrate. Then, the multilayer film was processed into a center size of 5×5μm by UV exposure and argon ion etching. 2 A cross-shaped device is used, and a wire is led out from each of the four ports of the cross device to test the magnetic resistance. One path of the cross is parallel to the easy axis direction of the NiFe plane, and current is passed along this direction. The degree of reversal of the magnetization moment in the NiFe plane is observed using a magneto-optical Kerr microscope.

[0035] Depend on Figure 3 The results of the magneto-optical Kerr microscope test at room temperature show that when the current density is 1.14×10 7 A cm -2 When the current density is 1.43×10 7 A cm -2 When the magnetic moment in the whole plane flips 180 degrees, the magnetic moment flips 180 degrees. The reason for the magnetic moment flip is that when a current parallel to the Néel magnetic moment is applied to the antiferromagnetic Mn2Au, the spins on the magnetic sublattice will produce spin rotation under the action of the spin-orbit effective field. Due to the broken symmetry of the sublattice of the antiferromagnetic Mn2Au, the same spin polarization σz in the z direction will be generated in the two sublattices. This perpendicular spin polarization spin current can replace the external magnetic field, so it can assist the spin current with spin polarization in the plane generated by the current passing through the heavy metal Mn2Au, and realize the flip of the NiFe in-plane magnetic moment without the assistance of the external magnetic field.

Claims

1. A device that uses a vertically spin-polarized spin current to flip the magnetic moment without the assistance of a magnetic field, which comprises, from bottom to top, a substrate, a strong spin-orbit coupling layer and a magnetization layer; The strong spin-orbit coupling layer is made of at least one of the following materials: a topological insulator material, an antiferromagnetic material having both sublattice center inversion symmetry breaking and global center inversion symmetry; the topological insulator material includes Bi2Se3 and / or Bi2Te3; the antiferromagnetic material having both sublattice center inversion symmetry breaking and global center inversion symmetry includes Mn2Au and CuMnAs; The magnetic layer includes a material having a perpendicular easy magnetization and / or a material having an in-plane easy magnetization axis.

2. The device according to claim 1, characterized in that: The substrate is a crystalline substrate with high crystal asymmetry; The type of crystal substrate having high crystal asymmetry is selected from at least one of MgO (110), MgO (111) and PMN-PT (011).

3. The device according to claim 1 or 2, characterized in that: The material having perpendicular easy magnetization includes at least one of CoFeB, Co / Ni multilayer film and Co / Pt multilayer film; The material having an in-plane easy magnetization axis includes at least one of NiFe, Co and Fe.

4. The method for preparing a device that uses a vertically spin-polarized spin current to assist in switching magnetic moments without a magnetic field as described in any one of claims 1 to 3, comprising the following steps: depositing the strong spin-orbit coupling layer and the magnetization layer on the substrate in sequence, thereby obtaining the device that uses a vertically spin-polarized spin current to assist in switching magnetic moments without a magnetic field.

5. The preparation method according to claim 4, characterized in that: The strong spin-orbit coupling layer and the magnetization layer are deposited by magnetron sputtering and / or electron beam evaporation.

6. The preparation method according to claim 4 or 5, characterized in that: The device that uses a vertically spin-polarized spin current to assist in flipping the magnetic moment without a magnetic field also includes a device processed into a cross-shaped center through the steps of ultraviolet exposure, development, and argon ion etching.

7. Use of the device according to any one of claims 1 to 3 for flipping magnetic moment using a vertically spin-polarized spin current without the assistance of a magnetic field in the preparation of a high-density, low-power information storage device.

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