CN112712830A - Nonvolatile regulation and control method for realizing voltage-induced nano-dot magnetization from uniaxial state to vortex state - Google Patents
Nonvolatile regulation and control method for realizing voltage-induced nano-dot magnetization from uniaxial state to vortex state Download PDFInfo
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Abstract
The invention discloses a voltage-induced nanodot magnetization uniaxial-to-vortex-state nonvolatile regulation and control method, and aims to solve the problem of high energy consumption in the process of electrically driving a low-energy-consumption nanodot in a uniaxial state to a vortex state. The technical scheme is as follows: a nonvolatile nano-point magnetization uniaxial-vortex voltage regulation and control system is designed, wherein the nonvolatile nano-point magnetization uniaxial-vortex voltage regulation and control system consists of a piezoelectric layer, a bottom electrode, N magnetic nano-points and two short circuit surface electrodes, the elliptic magnetic nano-points which are isolated from each other on the piezoelectric layer are constructed between the two short circuit surface electrodes, and the long axis direction is parallel to a connecting line of the two short circuit surface electrodes. After the magnetization state of the magnetic nanodots is initialized to a uniaxial state by applying a magnetic field, a voltage is applied between the short circuit surface electrode and the bottom electrode to generate stress so that the magnetic nanodots are converted from the uniaxial state to a vortex state. The method successfully realizes the stable voltage regulation and control from the magnetization uniaxial state to the vortex state of the magnetic nanodots and solves the problem of high energy consumption in the conversion from the uniaxial state to the vortex state of the electrically-driven low-energy consumption nanodots.
Description
Technical Field
The invention relates to a low-power consumption nanodot magnetization regulation method, in particular to a voltage-induced nanodot magnetization uniaxial state to vortex state regulation method.
Background
In ferromagnetic materials and nanostructures, the magnetic vortex state is considered to be an ideal base cell for spintronic logic devices and low-power magnetic random access memories due to its stable non-volatile magnetic logic feature configuration at room temperature. A vortex regime typically has four characteristic configurations, including vortex chirality (clockwise or counterclockwise) and out-of-plane magnetization direction (up or down), which facilitates encoding logic. Since the vortex state of a magnetic disk at room temperature is naturally non-volatile and has no internal power consumption, the main problems to be solved in logic and storage applications in the field of spintronics are the compression of the disk size and the external regulation of low power consumption.
To this end, researchers have conducted many useful studies. Shinjo et al, Magnetic Vortex Core Observation in Circular Dots of Permalloy (Science,289,930-932), in 2000, succeeded in observing stable magnetized Vortex states in micron-sized Permalloy disks with 1.5T Magnetic field regulation. In Vortex Core-drive Magnetization Dynamics (Science,304,420-422) in 2004, Choe et al used magnetic pulses to drive the Magnetization Vortex of micron-sized rectangular CoFe thin films. Hertel et al, in < Ultrafast Nano Toggle of Vortex Cores > (Phys. Rev. Lett.,98,117201.1-117201.4) 2007 simulate magnetic field pulse-controlled Vortex core polarity Switching. 2013 Magnetic Vortex Dynamics in Thickness-modulated Ni80Fe20Disks (thickness modulated Ni)80Fe20Magnetic vortex dynamics in magnetic disks) Shimon et al, physics, rev.b,87,214422, studied thickness modulation on disk vorticesThe influence of (c). However, the researches depend on the regulation and control of an external magnetic field, so that the external energy consumption is increased, and the low energy consumption advantage of the vortex state is lost. Finizio et al in Phys.Rev.App.,1,021001, "Magnetic Anisotropy Engineering in Thin Film Ni Nanostructures by Magnetoelastic Coupling study" (Phys.Rev.App.,1,021001) successfully produced Magnetic vortices in micron-sized Ni-oriented films by using Magnetoelastic Coupling, and provide effective exploration for regulating Magnetic vortices by electrical methods. Researchers achieve polarity switching of time-varying stress regulation vortex cores, stress regulation generated by voltage achieves uncertain vortex chiral switching, and voltage driving achieves vortex summation generation and assembly in micron-sized Ni magnetic disks. In the researches, magnetostrictive materials are cast on a piezoelectric substrate, and voltage is used for regulating and controlling magnetized vortex through the action of inverse magnetoelectric coupling, so that a competitive method is provided for regulating and controlling low-energy-consumption vortex. However, the disk has another non-volatile low energy state, i.e., a uniaxial state, in addition to the vortex state. Once the nano-dots based on the vortex state enter the uniaxial state, the nano-dots cannot be restored to the vortex state again. Therefore, the control of the uniaxial state to the vortex state has great significance for the application of the vortex state nanodots in logic storage and calculation.
Jausovec et al in Cycle-by-Cycle Observation of Single-domain-to-vortex Transitions in Magnetic nanodiscs (App. Phys. Lett.,88(5),5822) simulated the regulation of permalloy nanodots from uniaxial to vortex state by Magnetic field in 2006. However, this method requires a strong current to pass through the wires to generate a strong magnetic field, which results in a large power consumption. In 2016 (Nano Lett.,16 (9)), 5681-5687, Sampath et al, who utilized stress generated by sound waves, successfully realized the uniaxial to Vortex state regulation of hundred-nanometer-sized Co nanodots, however, electrodes required for generating sound waves would waste a large area, and the integration density of a Vortex memory is reduced.
Bhattacharya et al in' Incoent Magnetization dynamics of magnetic induced shrinkage of magnetostrictive nano magnets (Nanotechnology,28,015202) conducted theoretical research on the transformation from uniaxial state to vortex state of a multi-iron nanodot driven by stress generated by voltage, and provided a thought for the low-energy consumption electrical regulation nanodot from uniaxial state to vortex state.
Therefore, the current nanodot magnetization uniaxial-eddy regulation and control method either needs excessive energy consumption or wastes excessive unit memory area so as to be difficult to integrate, and cannot meet the requirements of a new generation of magnetic storage and calculation circuit. Although the Bhattacharya research provides theoretical support for the magnetization state switching from the voltage regulation nanodot single axis to the vortex state and provides a low-energy consumption regulation idea, the idea is still in a theoretical stage, and no reliable experiment proves the correctness of the idea so far and no specific scheme for utilizing stress to regulate the magnetization state is disclosed.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a voltage-induced nanodot magnetization uniaxial-to-vortex-state nonvolatile regulation and control method, which solves the high energy consumption problem in the electric-driven low-energy-consumption nanodot uniaxial-to-vortex-state conversion, so that a vortex-state nonvolatile memory can be better applied to a low-energy-consumption magnetic logic circuit and a storage system.
The technical scheme adopted by the invention for solving the technical problems is as follows:
firstly, designing a nonvolatile nano-dot magnetization uniaxial-vortex voltage regulation and control system, wherein the system consists of a piezoelectric layer, a bottom electrode, N (N is a positive integer) magnetic nano-dots and two short-circuit surface electrodes. Defining the connecting line of the central points of the two short-circuit surface electrodes as OO ', wherein the distance between the two short-circuit surface electrodes in the OO' direction is n, and constructing the upper surface of the piezoelectric layer by using a micro-nano processing technology. The N magnetic nanodots are also constructed on the upper surface of the piezoelectric layer by using a micro-nano processing technology, and are all positioned in a rectangular space with the length of N and the width of c between the two short circuit surface electrodes 1. The bottom electrode is constructed on the lower surface of the piezoelectric layer by using a micro-nano processing technology. The width c is equal to the side length of the short-circuited meter electrode.
The piezoelectric layer is generally a film with a certain piezoelectric coefficient, the thickness is th, the th is generally between 400nm and 5mm, the shape is not required, and the piezoelectric layer can be formed as long as the upper surface area meets the requirement of constructing N magnetic nano-dots and two short-circuit surface electrodes. The material is PMN-PT (Pb (Mg)1/3Nb2/3)O3-PbTiO3) Piezoelectric coefficient d of PMN-PTeff＝(d31-d32)/(1+v)，d31Is the PMN-PT in-plane piezoelectric coefficient, d31＝-3000pm/V,d32Is the out-of-plane piezoelectric coefficient of PMN-PT, d321000pm/V, V is Poisson coefficient V0.3, and crystal orientation is [011]]。
The short-circuit meter electrode is a square body with a certain thickness, the side length is c, the thickness is h, and the material is gold (namely Au). c is generally between 50nm and 50mm and h is generally between 50nm and 1000 nm. The center lines OO' of the two short circuit surface electrodes are along the [010] direction, i.e., the long axis direction of the magnetic nanodots. The distance n between the two short-circuit meter electrodes is 2 times the thickness th of the piezoelectric layer, and this distance can ensure that local directional stress is generated between the two short-circuit meter electrodes after voltage is applied, and the direction of the directional stress is along the central line OO' of the two short-circuit meter electrodes.
The magnetic nano-point material is ferromagnetic metal Ni, and the Young modulus Y of the Ni is 2.14 multiplied by 1011Pa. Since Ni is a polycrystalline ferromagnetic material, although it has magnetic properties, magnetocrystalline anisotropy of Ni atoms cannot generate an easy magnetization axis due to disorder of the arrangement of Ni atoms, and it does not exhibit magnetic properties to the outside at room temperature.
The magnetic nanodots are in the shape of elliptic cylinders, i.e. two bottom surfaces are elliptic (only the bottom surface is elliptic as compared with a cylinder), the size is a x b x l, a is a short axis, b is a long axis, and l is the thickness, wherein l < a < b. a and b are generally between 50nm and 1000nm, and l is generally between 5nm and 50 nm. The long axis direction of the ellipse of the bottom surface of the magnetic nanodots is parallel to the central line OO' of the two short circuit surface electrodes, and the N magnetic nanodots can be subjected to in-plane compressive stress and out-of-plane tensile stress due to the high magnetostriction coefficient of the Ni material, so that the magnetization state is changed, and the magnetization state is regulated from a uniaxial state to a vortex state. All the magnetic nanodots are isolated, the center-to-center distance d between every two adjacent magnetic nanodots is ensured to be negligible, the center-to-center distance d between every two adjacent magnetic nanodots is greater than 2b, and b is the major axis of an ellipse. The empirical value of d is 2 microns.
The bottom electrode is grounded, the thickness is m, and the material is gold (namely Au). m is generally between 50nm and 1000 nm.
Secondly, a nonvolatile nano-point magnetization single-axis-vortex voltage regulation and control system is adopted to regulate and control the magnetic nano-point magnetization single-axis-vortex, and the method comprises the following steps:
2.1 applying a uniform magnetic field with a size of 0.2T (+ -0.02T) to the N magnetic nanodots along the central line OO' direction of the two short-circuit surface electrodes to initialize the magnetization states of the N magnetic nanodots to uniaxial states, wherein the time for applying the magnetic field is generally more than 1 ns.
And 2.2, applying a voltage of-200V to the position between the short-circuit meter electrode and the bottom electrode by using a direct-current voltage source, wherein the positive electrode of the voltage source is connected with the short-circuit electrode, and the negative electrode of the power source is connected with the bottom electrode (and is simultaneously grounded), namely, applying voltage to the piezoelectric layer to deform the piezoelectric layer. A deformation stress is formed between the shorted meter electrode and the bottom electrode. The time for applying the voltage is not particularly limited (since the whole regulation process generally only needs 1ns, the time is hard to control manually, therefore, the time for applying the voltage is generally more than 1ns), and the average vertical electric field intensity formed between the short circuit surface electrode and the bottom electrode is 0.4 MV/m. The deformation stress is conducted to the magnetic nanodots to generate stress in the long axis direction of the magnetic nanodots; the stress causes the magnetic nanodots to transform from a uniaxial state to a non-volatile vortex state; the dc voltage source is removed.
2.3 the voltage to stress and the stress to magnetization state transition time only need 1ns, and after applying the voltage, the magnetization of the magnetic nanodots is observed by using a magnetic microscope, and the N magnetic nanodots are all found to enter a stable nonvolatile vortex state.
The invention has the following beneficial effects:
1. the nonvolatile nanodot magnetization uniaxial-vortex voltage regulation and control system applies voltage between the electrodes on the upper surface and the lower surface of the piezoelectric layer under the condition of no external magnetic field or needing overlarge unit memory area, so that the piezoelectric layer is deformed. The deformation is conducted to the magnetic nanodots to change the magnetization state of the magnetic nanodots, and further, the stable voltage regulation from the magnetic uniaxial state to the vortex state of the magnetic nanodots is successfully realized. After the voltage was removed, a distinct vortex state was observed using a magnetic microscope. When the voltage is removed or applied again, the vortex state of the nano-dots is stable and nonvolatile. The method has important significance for electrical regulation and control of the vortex-based spintronic device.
2. The invention solves the problem of high energy consumption in the process of electrically driving the low-energy consumption nanodot single-axis state to the vortex state, so that the vortex nonvolatile memory can be better applied to low-energy consumption magnetic logic circuits and storage systems.
Drawings
FIG. 1 is a general flow diagram of the present invention; FIG. 2 is a logic structure diagram of a non-volatile nano-dot magnetization uniaxial-vortex voltage regulation system designed in the first step of the invention;
FIG. 3 is a diagram showing the magnetization state of nanodots photographed by the magnetic microscope of example 1;
fig. 4 shows the process of changing the magnetic moment from the magnetization single axis to the vortex of the magnetic nanodots in example 1 by the micro-magnetic simulation.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
as shown in fig. 1, the present invention comprises the steps of:
firstly, a nonvolatile nano-dot magnetization uniaxial-vortex voltage regulation and control system is designed, and as shown in fig. 2, the system is composed of a piezoelectric layer 2, a bottom electrode 4, N (N is a positive integer) magnetic nano-dots 3 and two short-circuit surface electrodes 1. Defining the connecting line of the central points of the two short-circuit surface electrodes 1 as OO ', wherein the distance between the two short-circuit surface electrodes 1 in the OO' direction is n, and constructing the upper surface of the piezoelectric layer 2 by using a micro-nano processing technology. The N magnetic nanodots 3 are also constructed on the upper surface of the piezoelectric layer 2 by using a micro-nano processing technology, and the N magnetic nanodots 3 are all positioned in a rectangular space with the length of N and the width of c between the two short circuit surface electrodes 1. The bottom electrode 4 is constructed on the lower surface of the piezoelectric layer 2 by using a micro-nano processing technology. The width c is equal to the side length of the short-circuit list electrode 1.
The piezoelectric layer 2 is generally a thin film with a certain piezoelectric coefficient, the thickness is th, the th is between 400nm and 5mm, the shape is not required, and the upper surface area is enough to construct N magnetic nano-dots 3 and two short-circuit surface electrodes 1. The material is PMN-PT (Pb (Mg)1/3Nb2/3)O3-PbTiO3) Piezoelectric coefficient d of PMN-PTeff＝(d31-d32)/(1+v)，d31Is the PMN-PT in-plane piezoelectric coefficient, d31＝-3000pm/V,d32Is the out-of-plane piezoelectric coefficient of PMN-PT, d321000pm/V, V is Poisson coefficient V0.3, and crystal orientation is [011]]。
The short-circuit surface electrode 1 is a square body with a certain thickness, the side length is c, the thickness is h, and the material is gold (namely Au). c is between 50nm and 50mm and h is between 50nm and 1000 nm. The center lines OO' of the two short circuit surface electrodes 1 are along the [010] direction, i.e., the long axis direction of the magnetic nanodots 3. The distance n between the two short-circuit meter electrodes 1, which is 2 times the thickness th of the piezoelectric layer 2, ensures that a local directional stress is generated between the two short-circuit meter electrodes 1 after the application of a voltage, the direction of the directional stress being along the center line OO' of the two short-circuit meter electrodes 1.
The magnetic nano-dot 3 material is ferromagnetic metal Ni, and the Young modulus Y of the Ni is 2.14 multiplied by 1011Pa。
The magnetic nanodots 3 are in the shape of elliptic cylinders, i.e. the two bottom surfaces are ellipses with the size of a × b × l, a is the short axis, b is the long axis, l is the thickness, wherein l < a < b. a and b are between 50nm and 1000nm, l is between 5nm and 50 nm. The major axis direction of the ellipse of the bottom surface of the magnetic nanodots 3 is parallel to the center line OO' of the two short circuit surface electrodes 1, and since the Ni material has a high magnetostriction coefficient, the N magnetic nanodots 3 are subjected to in-plane compressive stress and out-of-plane tensile stress, so that the magnetization state is changed, and the magnetization state is regulated from a uniaxial state to a vortex state. All the magnetic nanodots are isolated, the center-to-center distance d between every two adjacent magnetic nanodots 3 is ensured to be negligible, the center-to-center distance d between every two adjacent magnetic nanodots 3 is greater than 2b, and b is the major axis of the ellipse. The empirical value of d is 2 microns.
The bottom electrode 4 is grounded, has a thickness of m and is made of gold (i.e., Au). m is between 50nm and 1000 nm.
Secondly, a nonvolatile nano-point magnetization single-axis-vortex voltage regulation and control system is adopted to regulate and control the magnetic nano-point magnetization single-axis-vortex, and the method comprises the following steps:
2.1 applying a uniform magnetic field of 0.2T (± 0.02T) to the N magnetic nanodots 3 along the central line OO' direction of the two short-circuit surface electrodes 1, initializing the magnetization state of the N magnetic nanodots 3 to a uniaxial state, and applying the magnetic field for more than 1 ns.
And 2.2, applying a voltage of-200V to the space between the short-circuit meter electrode 1 and the bottom electrode 4 by using a direct-current voltage source, wherein the positive electrode of the voltage source is connected with the short-circuit electrode 1, and the negative electrode of the power source is connected with the bottom electrode 4 (and is simultaneously grounded), namely, applying voltage to the piezoelectric layer to deform the piezoelectric layer. A deformation stress is formed between the short-circuited counter electrode 1 and the bottom electrode 4. The time for applying the voltage is not particularly limited, and the time for applying the voltage is more than 1ns, and the average vertical electric field intensity formed between the short circuit meter electrode 1 and the bottom electrode 4 is 0.4 MV/m. The deformation stress is conducted to the magnetic nanodots 3, and stress is generated in the long axis direction of the magnetic nanodots 3; the stress causes the magnetic nanodots 3 to transform from a uniaxial state to a non-volatile vortex state; the dc voltage source is removed.
2.3 the voltage to stress and stress to magnetization state transition time only needs 1ns, and after applying voltage, magnetic force microscope is used to observe the magnetization of the magnetic nanodots 3, and it is found that the N magnetic nanodots 3 all enter into stable non-volatile vortex state.
Example 1:
a pair of short-circuited surface electrodes 1 having a side length c of 0.5mm and a thickness h of 100nm are formed on a piezoelectric layer 2 having a crystal orientation [011] and a thickness th of 0.5mm by electron beam evaporation and lift-off. Next, 4(N ═ 4) elliptic cylindrical magnetic nanodots 3 having a size of 324nm × 360nm × 24nm (a × b × l) were constructed between the two short circuit counter electrodes 1, and the long axis direction of the magnetic nanodots 3 was parallel to the center line OO' of the 2 short circuit counter electrodes 1. The center-to-center distance d between two adjacent magnetic nanodots 3 is 2 micrometers. The grounded bottom electrode 4 has a thickness m of 200 nm.
The magnetization state of all the magnetic nanodots 3 is initialized to a uniaxial state by first applying a magnetic field of-0.2T in the long axis direction (i.e., OO' direction) of the magnetic nanodots 3. Then, a voltage of-200V was applied between the short-circuited meter electrode 1 and the bottom electrode 4, and the average vertical electric field intensity was 0.4 MV/m. The stress magnitude σ can be generated by the formula σ ═ YdeffU/th, where the Young's modulus Y of Ni is 2.14X 1011Piezoelectric coefficient d of Pa, PMN-PTeff＝(d31-d32) /(1+ v). Piezoelectric coefficient d in PMN-PT plane31＝-3000pm/V,d321000pm/V and 0.3 poisson coefficient V. When th is 0.5mm, the applied voltage will generate a stress of 263MPa to the Ni nanodots in the long axis direction. The magnetization of the nanodots after the voltage application was observed using a magnetic microscope, and the nanodots were found to enter a stable non-volatile vortex state.
Fig. 3(a) is a topography of four magnetic nanodots 3 observed by an atomic force microscope, and it can be seen from fig. 3(a) that the four magnetic nanodots 3 are all in the shape of an elliptic cylinder and have a thickness of 24 nm. An initialization magnetic field of-0.2T is applied in the direction along the long axis of the magnetic nanodots 3. The magnetization of the magnetic nanodots 3 was observed using a magnetic force microscope to obtain a topography as shown in fig. 3 (b). It can be seen from fig. 3(b) that the magnetization of the regions of four magnetic nanodots 3 can be observed using the elevated 75nm mode test phase diagram after the atomic force microscope is equipped with the magnetic probe. The light areas in fig. 3(b) indicate repulsive force between the magnetization of the magnetic nanodots 3 and the magnetic probes, and the dark areas indicate attractive force between the magnetic nanodots 3 and the magnetic probes. As shown in fig. 3(b), both ends of the four nanodots are half light and half dark, indicating that the magnetization state is all successfully initialized to a uniaxial state. Then, a voltage of 0.4MV/m is applied between the short-circuit meter electrode 1 and the bottom electrode 4, and the magnetization state of the magnetic nanodots 3 is regulated and controlled by the reverse magnetoelectric action. After the voltage was removed, the magnetization state of the nanodots was observed using a magnetic microscope, and as shown in fig. 3(c), the patterns of four magnetic nanodots 3 alternate bright and dark, indicating that the magnetization state was successfully modulated from the uniaxial state to the vortex state. The vortex state obtained by regulation is nonvolatile and still keeps stable under the interference of room temperature thermal noise. Even if the voltage is applied again, the vortex state of the nanodots is not changed.
Simulation verification:
in order to analyze the process of the nano-dot magnetization from a uniaxial state to a vortex state under the voltage regulation, simulation calculation is carried out on the dynamic magnetization process of the magnetic nano-dot by using Mumax 3. The dimensional parameters were the same as in the experimental case. The size of the simulated grid (finite difference method calculation unit used by simulation software) is 6nm × 6nm × 6nm, and the parameters of the material Ni used for simulating the magnetic nanodots 3 are as follows: damping coefficient α is 0.045, saturated magnetostriction λs＝-2×10-5Saturation magnetization Ms＝4.84×105A/m, exchange constant A1.05X 10-11J/m and stress 150 MPa.
Given the initial magnetization direction [010] of the magnetic nanodots 3, i.e., in the long axis direction, as shown in fig. 4(a), under thermal noise, the uniaxial state (all magnetic moments pointing upward) of the magnetic nanodots 3 is disturbed, thereby becoming magnetized as shown in fig. 3 (b). Next, a stress (generated by applying a simulated voltage) of 150MPa is applied to the magnetic nanodots 3 along the long axis direction thereof, and in order to simulate the rising edge and the falling edge of the voltage during the experiment, a square wave having a pulse width of 5ns and a period of 20ns is subjected to fourier expansion, and the first two simulated stress pulses are taken. The magnetization state of the magnetic nanodots 3 is transformed into a clockwise vortex state by stress, as shown in fig. 4 (c). Here clockwise and counterclockwise are related to the magnetization component of the magnetic nanodots 3 when relaxed at room temperature. If the magnetization component has a component in the counterclockwise direction, the swirling of the nanodots under stress will be counterclockwise. After the stress is removed, the nanodots remain in a vortex state, as shown in fig. 4 (d). Even if this stress is applied again, the nanodots remain in a vortex state. This vortex state is non-volatile. The simulation further proves the effectiveness of the invention through calculation.
The external energy consumption generated by the regulation and control of the invention can be 2A multiplied by epsilonrε0U2Calculated as/th, is about 0.175 uJ (micro-coke, i.e., 10)- 6J) Wherein the dielectric constant ε of the piezoelectric layer 2rAnd a thickness th of 500 and 0.5mm, respectively, a being the area of a single short-circuit-table electrode 1, 0.5mm x 0.5 mm. Although high voltage is required to regulate the nanodots to enter the vortex state due to the large thickness of the piezoelectric layer 2, if the major axis b and the minor axis a of the magnetic nanodots 3, the side length c of the short circuit surface electrode 1 and the thickness th of the piezoelectric layer 2 are reduced, the required voltage and power consumption can be reduced by several orders of magnitude. For a system with the thickness th of the piezoelectric layer 2 being 500nm, the long axis b and the short axis a of the magnetic nanodots 3 and the side length c of the surface electrode being about 100nm, the energy required by the method for regulating and controlling the primary voltage is only a few aJ (namely 10)-18J) In that respect Therefore, under the condition that the device processing precision is enough, the method is expected to realize the voltage regulation of the magnetic nano-point uniaxial state-vortex state with ultra-low power consumption.
Claims (10)
1. A nonvolatile regulation and control method for a voltage-induced nanodot magnetization from a uniaxial state to a vortex state is characterized by comprising the following steps of:
firstly, designing a nonvolatile nano-point magnetization uniaxial-vortex voltage regulation and control system, wherein the system consists of a piezoelectric layer (2), a bottom electrode (4), N magnetic nano-points (3) and two short-circuit surface electrodes (1), and N is a positive integer; defining the central point connecting line of the two short circuit meter electrodes (1) as OO ', wherein the distance between the two short circuit meter electrodes (1) in the direction of OO' is n, and constructing the two short circuit meter electrodes on the upper surface of the piezoelectric layer (2); the N magnetic nanodots (3) are constructed on the upper surface of the piezoelectric layer (2), and the N magnetic nanodots (3) are all positioned in a rectangular space with the length of N and the width of c between the two short circuit surface electrodes (1); the bottom electrode (4) is constructed on the lower surface of the piezoelectric layer (2); c is the side length of the short-circuit meter electrode (1);
the piezoelectric layer (2) is a thin film with a thickness th and is made of PMN-PT (Pb (Mg)1/3Nb2/3)O3-PbTiO3；
The short circuit surface electrode (1) is a square body, the thickness is h, and the material is gold, namely Au; the central lines OO' of the two short-circuit meter electrodes (1) are along the [010] direction, namely the long axis direction of the magnetic nanodots (3); the distance n between the two short-circuit meter electrodes (1) is required to ensure that local directional stress is generated between the two short-circuit meter electrodes (1) after voltage is applied, and the direction of the directional stress is along the central lines OO' of the two short-circuit meter electrodes (1);
the magnetic nano-dots (3) are made of ferromagnetic metal Ni;
the magnetic nanodots (3) are in an elliptic cylinder shape, namely two bottom surfaces are elliptic, the size is a multiplied by b multiplied by l, a is a short axis, b is a long axis, and l is the thickness, wherein l < a < b; the direction of the long axis of the ellipse of the bottom surface of each magnetic nanodot (3) is parallel to the central line OO' of each short-circuit meter electrode (1), all the magnetic nanodots are isolated, and the central distance d between every two adjacent magnetic nanodots (3) meets the requirement of ensuring that the dipole coupling effect between every two magnetic nanodots can be ignored;
the bottom electrode (4) is grounded, the thickness is m, the material is gold, and m is generally between 50nm and 1000 nm.
Secondly, a nonvolatile nano-point magnetization single-axis-vortex voltage regulation and control system is adopted to regulate and control the magnetic nano-point magnetization single-axis-vortex, and the method comprises the following steps:
2.1 applying a uniform magnetic field to the N magnetic nanodots (3) along the central line OO' direction of the two short-circuit meter electrodes (1) to initialize the magnetization states of the N magnetic nanodots (3) to be uniaxial states;
2.2 applying voltage between the short-circuit meter electrode (1) and the bottom electrode (4) by using a direct-current voltage source, wherein the positive electrode of a power supply is connected with the short-circuit electrode 1, and the negative electrode of the power supply is connected with the bottom electrode (4), namely applying voltage to the piezoelectric layer to generate deformation stress; the deformation stress is conducted to the magnetic nanodots (3), and stress is generated in the long axis direction of the magnetic nanodots (3), so that the magnetic nanodots (3) are converted from a uniaxial state to a vortex state; the dc voltage source is removed.
2.3 observing the magnetization of the magnetic nanodots (3) by using a magnetic microscope, and finding that the N magnetic nanodots (3) all enter a stable vortex state.
2. The non-volatile regulation and control method of the voltage-induced nano-dot magnetization from the uniaxial to the vortex state according to claim 1, characterized in that the two short-circuit surface electrodes (1) and the N magnetic nano-dots (3) are constructed on the upper surface of the piezoelectric layer (2) by using a micro-nano processing technology, and the bottom electrode (4) is constructed on the lower surface of the piezoelectric layer (2) by using a micro-nano processing technology.
3. The method for nonvolatile regulation of uniaxial to vortex state of voltage-induced nanodot magnetization according to claim 1, wherein the thickness th of the piezoelectric layer (2) is between 400nm and 5mm, and the upper surface area of the piezoelectric layer (2) is sufficient to construct N magnetic nanodots (3) and two short-circuit surface electrodes (1).
4. The method for non-volatile modulation of uniaxial to vortex state of voltage-induced nanodot magnetization according to claim 1, wherein the crystal orientation of the piezoelectric layer (2) is [011 ].
5. The method for nonvolatile regulation of uniaxial to vortical states of voltage-induced nanodot magnetization according to claim 1, wherein the short-circuited surface electrode (1) has a side length c of 50nm to 50mm and a thickness h of 50nm to 1000 nm; the distance n between the two short-circuit meter electrodes (1) is 2 times the thickness th of the piezoelectric layer (2).
6. The method for the non-volatile regulation of uniaxial to vortex state of voltage-induced nanodot magnetization according to claim 1, wherein a and b of the magnetic nanodots (3) are between 50nm and 1000nm, l is between 5nm and 50 nm; the center-to-center distance d between two adjacent magnetic nanodots (3) satisfies d >2 b.
7. The method of claim 6, wherein d is 2 μm.
8. The method for non-volatile modulation of uniaxial to vortical states of voltage-induced nanodot magnetization according to claim 1, wherein the bottom electrode (4) has a thickness m between 50nm and 1000 nm.
9. The method for nonvolatile regulation of uniaxial to vortex state of voltage-induced nanodot magnetization according to claim 1, wherein the applied magnetic field in step 2.1 has a magnitude of 0.2 ± 0.02T and the time of application is more than 1 ns.
10. The method for nonvolatile regulation of uniaxial to vortical states of voltage-induced nanodot magnetization according to claim 1, wherein 2.2 steps of the voltage applied between the short-circuited surface electrode (1) and the bottom electrode (4) is-200V, and the average vertical electric field intensity is 0.4 MV/m.
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