Method and application for measuring activation energy and characteristic relaxation time of phase transition process of nanomagnetic structure

Abstract

The present invention provides a method and application for measuring the activation energy and characteristic relaxation time of nanoscale magnetic structure phase transitions. This method utilizes the Lorentz mode of a transmission electron microscope to observe the dynamics of magnetic phase transitions in thin samples. By preparing thin samples with nanometer-scale thickness and geometric dimensions and using laser irradiation thermal demagnetization to eliminate the thermal retention effect of the magnetic phase transition, the method accurately obtains dynamic parameters such as the characteristic relaxation time and activation energy of nanoscale magnetic structure phase transitions. This method provides a novel and practical method for characterizing the magnetodynamic processes and intrinsic magnetic properties of magnetic materials.

Description

Technical Field

[0001] The present invention relates to the field of high spatial resolution and micro-nanoscale magnetic measurement technology, and specifically to a method for measuring the activation energy and characteristic relaxation time of a nanomagnetic structure phase transition process at the nanoscale. Background Art

[0002] The existing technology obtains the kinetic parameters of the magnetic phase transition process by measuring the macroscopic electromagnetic transport mode or SQUID / VSM and other magnetometry methods. For example, the information of the magnetic structure phase transition process can be obtained according to the change of the magnetoresistance of the magnetic material over time, and the kinetic parameters of the magnetic structure phase transition process (activation energy barrier E b Since these macroscopic magnetic measurement methods are only applicable to bulk samples, and bulk single crystal samples are usually difficult to obtain or have chaotic compositions, it is difficult to obtain reliable results on the magnetic phase transition dynamics of the samples.

[0003] In existing technical solutions, the specific changes in the micromagnetic structure are not visible, so it is necessary to develop new methods to measure the phase change process of the magnetic structure at the micro-nano scale with high spatial resolution. Summary of the Invention

[0004] Therefore, the purpose of the present invention is to overcome the defects in the prior art and provide a method and application for measuring the activation energy and characteristic relaxation time of the phase transition process of nanomagnetic structures at the nanoscale.

[0005] To achieve the above object, a first aspect of the present invention provides a method for measuring the activation energy and characteristic relaxation time of a nanomagnetic structure phase transition process, the method comprising the following steps:

[0006] (1) Preparation of nanometer-thick specimens suitable for transmission electron microscopy from bulk samples;

[0007] (2) Fixing the sample prepared in step (1) on a temperature-variable sample rod, and setting the temperature T of the thin sample by adjusting the heating current;

[0008] (3) Enabling the electron microscope objective lens in Lorentz working mode, applying a current intensity to it to generate the required external magnetic field to achieve the application of external magnetic fields of different intensities to the sample;

[0009] (4) Record the time point t when the magnetic structure phase change in the sample is completed f ;

[0010] (5) Turn off the electron microscope objective current, heat the sample to a temperature higher than the Curie temperature of the sample, and demagnetize the sample so that the magnetic structure returns to its initial state, thereby removing the hysteresis effect of the magnetic structure phase change process;

[0011] (6) Repeat steps (2) to (5) to obtain the relaxation time required for the magnetic structure phase transition of the sample at different temperatures;

[0012] (7) The magnetic structure transition time t measured at different temperatures T f , fitting according to the Arrhenius formula, and obtaining the activation energy and characteristic relaxation time of the thermodynamic process of magnetic structure phase transition in the sample.

[0013] According to the method of the first aspect of the present invention, in step (1), the thickness of the sample is 40 to 60 nm, preferably 45 to 50 nm.

[0014] According to the method of the first aspect of the present invention, in step (1), preparing a sample suitable for transmission electron microscopy observation from a bulk sample comprises the following steps:

[0015] (A) Polishing the surface of the bulk sample;

[0016] (B) placing the sample processed in step (A) on a focused ion beam processing platform and performing deposition protection using a PtC precursor gas;

[0017] (C) Dig a triangular groove longer than the protective layer on both sides of the protective layer;

[0018] (D) Continuously refine the end surface close to the protective layer in the triangular groove to reduce the sample thickness under the protective layer to 500-600 nm;

[0019] (E) Cutting the connection between the sample under the protective layer and the bulk sample, leaving only the supporting portion of the sample to be taken;

[0020] (F) Using a robotic arm to insert the nanoprobe close to the sample to be taken, while introducing PtC precursor gas to allow the sample to be taken to adhere to the probe tip;

[0021] (G) Cutting off all connections between the sample and the block, and transferring the sample to be taken to a dedicated sample stage of a transmission electron microscope using a nanoprobe;

[0022] (H) The transferred sample is thinned to a thickness below 80 nm, which is the thickness that high-energy electron beams can penetrate.

[0023] According to the method of the first aspect of the present invention, in step (2), the temperature T is 100-400K, preferably 100-250K.

[0024] According to the method of the first aspect of the present invention, in step (3), the current intensity is 0 to 0.65A, preferably 0 to 0.5A.

[0025] According to the method of the first aspect of the present invention, in step (4), the time point t at which the magnetic structure phase change in the sample is completed is recorded. f The following steps are involved:

[0026] (I) recording the magnetic contrast change information of the magnetic structure during the transformation process by recording image software;

[0027] (II) The magnetic structure image after the objective lens current is turned on, which is regarded as the time zero of the magnetic structure transition;

[0028] (III) Recording the image data of the completion process of the magnetic structure phase transition, and taking the time point when the magnetic structure no longer changes as the time required for the magnetic structure phase transition to complete t f .

[0029] According to the method of the first aspect of the present invention, in step (5), the method of heating the sample is pulsed or continuous laser irradiation.

[0030] According to the method of the first aspect of the present invention, in step (6), the number of repetitions is 4 to 8 times, preferably 6 times.

[0031] According to the method of the first aspect of the present invention, in step (7), the fitting method includes the following steps:

[0032] (a) The temperature T of the sample is the horizontal axis, and the time t required for the corresponding phase change to complete is the horizontal axis. f As the vertical coordinate, draw a relationship curve;

[0033] (b) According to the Arrhenius formula, the temperature T and time t f Perform fitting calculations on the data, and the Arrhenius formula is:

[0034] Where t0 is the characteristic relaxation time, K b is the Boltzmann constant, E b is the energy barrier for magnetic structure transition.

[0035] The second aspect of the present invention provides a method for characterizing the magnetodynamic process and / or intrinsic magnetic properties of a first magnetic material, the method comprising the method for measuring the activation energy and characteristic relaxation time of the phase transition process of a nanomagnetic structure as described in the first aspect.

[0036] The present invention discloses a method for measuring the activation energy and characteristic relaxation time of nanomagnetic phase transitions at the nanoscale. This method, based on the Lorentz magnetic contrast observation method using a transmission electron microscope, directly observes the time required for the magnetic phase transition to complete under different temperatures and external magnetic fields to obtain thermodynamic parameters closely related to the magnetic phase transition, such as the activation energy and characteristic relaxation time. First, the sample to be tested is processed into a thin nanometer-thick sample using focused ion beam processing technology. The thin sample is then mounted on a temperature-adjustable variable temperature sample stage. During the experiment, the temperature of the thin magnetic sample can be dynamically adjusted by the heating element (heating wire) and the cooling element (liquid nitrogen or liquid helium) on the variable temperature stage. By varying the objective current in the Lorentz electron microscope, an external magnetic field is applied to the thin sample to drive the magnetic phase transition (from phase A to phase B). The dynamic process of the magnetic phase transition in the thin sample is simultaneously observed and recorded. The time required for the complete transition from magnetic phase A to phase B is determined using Lorentz electron microscopy observations, which is recorded as the relaxation time required for the magnetic phase transition in the entire thin sample. After completing a magnetic phase transition at a specific temperature and external magnetic field, the objective electron microscope is turned off, and the sample is heated and demagnetized by laser irradiation. The thin sample temperature is reset, and the objective current is adjusted to apply an external magnetic field. At the newly set temperature and external magnetic field, the change in magnetic contrast is observed using the Lorentz electron microscope, and the relaxation time required for the magnetic structural phase transition at that temperature is recorded. Repeating the Lorentz electron microscope observations of the magnetic structural phase transition at different temperatures and external magnetic fields allows the relaxation time required for the magnetic structural phase transition to be determined, which is related to the sample temperature and external magnetic field. Finally, using known functions describing the relaxation process of the magnetic structural phase transition, thermodynamic parameters of the magnetic structural phase transition, such as the activation energy and characteristic relaxation time, are obtained.

[0037] In order to overcome the deficiencies of the existing technical solutions, the present invention provides a method for measuring the activation energy and characteristic relaxation time of the phase transition process of nanomagnetic structures at the nanoscale, which can effectively solve the problems raised by the background technology.

[0038] The technical solution adopted by the present invention to solve its technical problem is:

[0039] A method for measuring the activation energy and characteristic relaxation time of a nanomagnetic structure phase transition process at the nanoscale, comprising the following steps:

[0040] Step 100: preparing a transmission electron microscope thin sample with a thickness of nanometer level from a bulk sample by using a focused ion beam micromachining method;

[0041] Step 200: Fix the thin sample on a temperature-variable sample rod. The sample rod has a current heating function, and the temperature T of the thin sample can be set by adjusting the magnitude of the heating current.

[0042] Step 300: Start the objective lens current of the Lorentz electron microscope and apply appropriate current intensity to achieve applying magnetic fields of different intensities to the sample;

[0043] Step 400: Record the time t required for the magnetic structure phase change in the sample to complete. f ;

[0044] Step 500: Turn off the objective lens current and simultaneously use pulsed or continuous laser heating to thermally demagnetize the sample to eliminate the magnetic thermal hysteresis effect, that is, to restore the magnetic structure to its initial state;

[0045] Step 600: repeat steps 200, 300, 400, and 500 at least five times to obtain the transition time of the sample at different temperatures;

[0046] Step 700: The magnetic structure transition time t measured at different temperatures T is f , fitting is performed according to the Arrhenius formula to obtain the magnetic structure phase transition dynamics parameters in the sample to be tested, such as the activation energy barrier size and characteristic relaxation time.

[0047] As a preferred technical solution of the present invention, in step 400, the time t required for the magnetic structure phase change in the sample to be completed is determined. f The specific steps are:

[0048] Step 401, automatically and in detail recording the magnetic contrast variation information of the magnetic structure during the transformation process by controlling the image acquisition script program of the recording image software, so as to provide accurate data for the subsequent magnetic structure phase transition time scale assessment;

[0049] Step 402: The magnetic structure image after the objective lens current is turned on is regarded as the time zero point of the magnetic structure transition;

[0050] Step 403: Record the image data of the completion process of the magnetic structure phase change, and take the time point when the magnetic structure no longer changes as the time required for the completion of the magnetic structure phase change t f .

[0051] As a preferred technical solution of the present invention, in step 500, the specific operation steps of the sample rapid demagnetization are:

[0052] Step 501: Turn off the current of the objective lens previously used to generate the external magnetic field, so that the thin sample is in a zero magnetic field environment;

[0053] Step 502: A pulsed or continuous laser beam is introduced into the sample chamber of the transmission electron microscope and focused onto the sample. Laser irradiation is then used to rapidly thermally demagnetize the magnetic structure in the sample. This thermal demagnetization process effectively eliminates the thermal hysteresis effect of the magnetic phase transition, allowing for measurement of the magnetic phase transition dynamics at the next temperature.

[0054] As a preferred technical solution of the present invention, in step 700, the specific steps for calculating the activation energy barrier of the sample magnetic structure phase change are:

[0055] Step 701: Take the temperature T of the sample as the horizontal axis and the time t required for the corresponding magnetic phase change to complete. f As the vertical coordinate, draw a relationship curve;

[0056] Step 702: According to the Arrhenius formula, the temperature T and the time t f Perform fitting calculations on the data, and the Arrhenius formula is:

[0057] Where t0 is the characteristic relaxation time, K b is the Boltzmann constant, E b is the energy barrier for magnetic structure transition.

[0058] The present invention utilizes the Lorentz mode of a transmission electron microscope (TEM). By applying an external magnetic field to a sample through the objective lens of the TEM, the dynamic changes in the sample's microscopic magnetic structure are visually and specifically displayed to researchers in detail. A known function is then used to solve the energy barrier required to cross during the magnetic structure transition, thus solving the difficult problem of measuring the transition energy barrier between different magnetic structures. The present invention is based on the phenomenon that the magnetic moment structure of a sample continuously changes under external thermal disturbances. The time required for the relaxation process of the magnetic structure phase transition is related to the activation energy barrier required to cross, namely, the Arrhenius relationship: Where t0 is the characteristic relaxation time, K b is the Boltzmann constant, both are known quantities, and are determined by measuring the transition time t f and the sample temperature T, the magnetic phase transition activation energy barrier E can be determined b The numerical value and characteristic relaxation time t0.

[0059] The method of the present invention may have but is not limited to the following beneficial effects:

[0060] The present invention uses the Lorentz mode of a transmission electron microscope to observe the magnetic phase transition dynamics of thin samples. By preparing thin samples with nanometer-level thickness and geometric dimensions, and using laser irradiation thermal demagnetization to eliminate the thermal retention effect of the magnetic phase transition process, the characteristic relaxation time and activation energy and other dynamic parameters of the nanoscale magnetic structure phase transition are accurately obtained, providing a novel and practical method for characterizing the magnetic dynamics and intrinsic magnetic properties of magnetic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which:

[0062] Figure 1 A schematic flow chart of the method of the present invention is shown.

[0063] Figure 2 A schematic diagram showing the specific steps in the thin slice sample preparation process of the present invention is shown.

[0064] Figure 3 The schematic diagram of the structure of the magnetized sample and the sample demagnetization device in the present invention is shown.

[0065] Figure 4 The magnetic state diagram before and after the completion of the magnetic structure phase transition in the FeGe alloy of Example 2 and the relationship curve between the sample temperature and the completion time of the magnetic phase transition are shown; wherein, Figure 4 (1) shows the magnetic state diagram before the magnetic structure phase transition is completed in FeGe alloy. Figure 4 (2) shows the magnetic state diagram after the magnetic structure phase transition in FeGe alloy is completed. Figure 4 (3) shows the relationship between sample temperature and magnetic phase transition completion time.

[0066] Description of reference numerals:

[0067] 1. A reflector that changes the laser light path; 2. A laser introduced into the transmission electron microscope from an external light path; 3. A thin sample with a nanomagnetic structure in the electron microscope; 4. A pulsed or continuous laser source and light path; 5. The electromagnetic lens (objective lens) of the electron microscope; 6. A variable temperature sample rod. DETAILED DESCRIPTION

[0068] The present invention is further described below by way of specific examples. However, it should be understood that these examples are merely provided for more detailed and specific description and are not to be construed as limiting the present invention in any form.

[0069] This section provides a general description of the materials and experimental methods used in the experiments of the present invention. Although many of the materials and procedures used to achieve the purposes of the present invention are well known in the art, the present invention is described herein in as much detail as possible. It will be understood by those skilled in the art that, unless otherwise specified, the materials and procedures used in the present invention are well known in the art.

[0070] The materials and instruments used in the following examples are as follows:

[0071] Material:

[0072] Block samples were purchased from Alfa Aesar.

[0073] instrument:

[0074] Transmission electron microscope, model 2100F, was purchased from JEOL Ltd.

[0075] Example 1

[0076] This embodiment is used to illustrate the method of the present invention for measuring the activation energy and characteristic relaxation time of the phase transition process of a nanomagnetic structure.

[0077] like Figures 1 to 3 As shown, the present invention provides a method for measuring the activation energy barrier of magnetic structure transition at the nanoscale. Before the test, the bulk sample needs to be prepared into a nanoscale thin specimen, and the thin specimen is connected to a variable temperature sample rod and loaded into a transmission electron microscope. After the test starts, the temperature of the thin specimen is preset. When it stabilizes at the temperature, the objective lens current is started to place the specimen in an environment with an external magnetic field, and a CCD camera is used to record the entire magnetic structure phase transition process. After completing one recording, the process is repeated at at least four other temperatures. Finally, the measured magnetic structure transition time at different temperatures is substituted into the Arrhenius function. t0 is the characteristic relaxation time, K b is the Boltzmann constant, and the activation energy barrier of the transition of the magnetic structure of the sample is calculated.

[0078] The specific steps include:

[0079] Step 100: Prepare a transmission electron microscope thin sample with a nanometer thickness from a bulk sample using focused ion beam micromachining technology.

[0080] like Figure 2 As shown, before measuring the activation energy barrier of the magnetic structure transition of the sample to be tested, the bulk sample needs to be prepared into nanosheets with relatively regular shape and size.

[0081] In step 100, the specific steps of preparing the nanoscale thin film sample are:

[0082] Step 101: polishing the surface of the bulk sample;

[0083] Step 102: Place the processed sample on a focused ion beam processing platform. Select a specific location, i.e., an area where the sample surface is flat, smooth, intact, and clean. Deposit a PtC precursor gas for protection. The protective layer is approximately 800 nm thick.

[0084] Step 103: dig out a triangular groove slightly longer than the protective layer on both sides of the protective layer;

[0085] Step 104: continuously refining the end surface close to the protective layer in the triangular groove to reduce the thickness of the sample under the protective layer to 500-600 nm;

[0086] Step 105: Cut the connection between the sample under the protective layer and the bulk sample, leaving only a small area as a support for the sample to be taken;

[0087] Step 106: Use a robotic arm to insert the nanoprobe close to the sample to be taken, and at the same time introduce PtC precursor gas to make the sample to be taken adhere to the probe tip;

[0088] Step 107: Cut off all connections between the sample to be taken and the block, and transfer the sample to be taken to a dedicated sample stage of the transmission electron microscope using a nanoprobe;

[0089] Step 108: Thin the transferred sample. Specifically, use a gallium ion beam current of 30 kV and 2.5 nA to thin the sample to 500 nm, switch to 30 kV and 0.23 nA to thin it to 200 nm, then use 16 kV and 0.23 nA to thin it to 100 nm, and finally switch to 16 kV and 80 pA to cut it to less than 80 nm, so that it reaches a thickness that can be penetrated by high-energy electron beams.

[0090] Step 200: Fix the taken-out TEM sample on a low-temperature sample stage, and control the heating current intensity of the sample stage so that the temperature of the sample can be stabilized at a certain temperature T, which is approximately within the range of 30 to 40 K below the Curie temperature.

[0091] Step 300: Turn on the objective lens current of the transmitted electron and pass a suitable current intensity to apply an external magnetic field of appropriate intensity to the sample so that the magnetic structure in the sample can be transformed.

[0092] Step 400: Record the end time t of the magnetic structure transition in the sample. f .

[0093] In a preferred technical solution, in step 400, the time t required for the magnetic structure phase transition in the sample to be completed is determined. f The specific steps are:

[0094] Step 401, automatically and in detail recording the magnetic contrast variation information of the magnetic structure during the transformation process by controlling the image acquisition script program of the recording image software, so as to provide accurate data for the subsequent magnetic structure phase transition time scale assessment;

[0095] Step 402: The magnetic structure image after the objective lens current is turned on is regarded as the time zero point of the magnetic structure transition;

[0096] Step 403: Record the image data of the completion process of the magnetic structure phase change, and take the time point when the magnetic structure no longer changes as the time required for the completion of the magnetic structure phase change t f .

[0097] Step 500: Turn off the current of the objective lens and use laser heating to demagnetize the sample, that is, restore the magnetic structure to the initial state of the transformation.

[0098] In a preferred technical solution, in step 500, a pulsed or continuous laser is used to thermally demagnetize the test sample. This method allows the sample to return to the thermally demagnetized state after undergoing a magnetic structure phase change, thereby eliminating the magnetic thermal hysteresis effect and setting a consistent initial state and conditions for the next magnetic phase change process.

[0099] In a preferred technical solution, in step 500, the specific operation steps of rapid demagnetization of the sample are:

[0100] Step 501: Turn off the current of the objective lens previously used to generate the external magnetic field, so that the thin sample is in a zero magnetic field environment;

[0101] Step 502: A pulsed or continuous laser beam is introduced into the sample chamber of the transmission electron microscope and focused onto the sample. Laser irradiation is then used to rapidly thermally demagnetize the magnetic structure in the sample. This thermal demagnetization process effectively eliminates the thermal hysteresis effect of the magnetic phase transition, allowing for measurement of the magnetic phase transition dynamics at the next temperature.

[0102] like Figure 3 As shown, after recording a magnetic structure transition, the current in objective lens 5 is turned off, placing the thin sample in a zero-magnetic field environment. A laser beam 2 of sufficient energy is generated by a laser. After entering the sample chamber of the transmission electron microscope, it is illuminated by reflector 1 onto the thin sample supported by the variable-temperature sample holder 6, rapidly raising the sample's temperature above the Curie temperature. When laser 2 is removed, the magnetic structure in the thin sample quickly returns to its state before the magnetic structure transition.

[0103] Step 600: Control the current flowing through the temperature-variable sample rod to set the temperature of the thin sample. After the sample temperature stabilizes, repeat steps 300, 400, and 500. This step should be repeated at least four times.

[0104] In a preferred technical solution, in step 600, the detailed dynamic process of the magnetic structure phase transition is recorded visually to accurately determine the time required for the magnetic structure phase transition to be completed.

[0105] Step 700: The magnetic structure transition time t measured at different temperatures T is f , according to the Arrhenius formula t0 is the characteristic relaxation time, K b Fit the Boltzmann constant to obtain the activation energy barrier E of the magnetic structure phase transition in the sample to be tested. b Size and characteristic relaxation time t0.

[0106] In a preferred technical solution, in step 700, the specific steps for calculating the activation energy barrier of the sample magnetic structure phase transition are:

[0107] Step 701: Take the temperature T of the sample as the horizontal axis and the time t required for the corresponding magnetic phase change to complete. f As the vertical coordinate, draw a relationship curve;

[0108] Step 702: According to the Arrhenius formula, the temperature T and the time t f Perform fitting calculations on the data, and the Arrhenius formula is:

[0109] Where t0 is the characteristic relaxation time, K b is the Boltzmann constant, E b is the energy barrier for magnetic structure transition.

[0110] Example 2

[0111] This embodiment is used to illustrate the method of the present invention for measuring the activation energy and characteristic relaxation time of the phase transition process of a nanomagnetic structure.

[0112] Step 100: Prepare a transmission electron microscope thin sample with a nanometer-level thickness from a FeGe (atomic ratio of Fe:Ge=1:1) bulk sample using focused ion beam micromachining technology. The sample thickness is 50 nm.

[0113] like Figure 2 As shown, before measuring the activation energy barrier of the magnetic structure transition of the sample to be tested, the bulk sample needs to be prepared into nanosheets with relatively regular shape and size.

[0114] In step 100, the specific steps of preparing the nanoscale thin film sample are:

[0115] Step 101: polishing the surface of the bulk sample;

[0116] Step 102: Place the processed sample on a focused ion beam processing platform. Select a specific location where the sample surface is intact and smooth. Use PtC precursor gas for deposition protection. The deposition conditions are 30 kV, 80 pA, and the protective layer composition is Pt. The protective layer thickness is 800 nm.

[0117] Step 103: dig out a triangular groove slightly longer than the protective layer on both sides of the protective layer;

[0118] Step 104: continuously refine the end surface close to the protective layer in the triangular groove to reduce the thickness of the sample under the protective layer to 500 nm;

[0119] Step 105: Cut the connection between the sample under the protective layer and the bulk sample, leaving only a small area as a support for the sample to be taken;

[0120] Step 106: Use a robotic arm to insert the nanoprobe close to the sample to be taken, and at the same time introduce PtC precursor gas to make the sample to be taken adhere to the probe tip;

[0121] Step 107: Cut off all connections between the sample to be taken and the block, and transfer the sample to be taken to a dedicated sample stage of the transmission electron microscope using a nanoprobe;

[0122] Step 108 : Thinning the transferred sample to reduce the sample thickness to 50 nm, which is the thickness that can be penetrated by the high-energy electron beam.

[0123] Step 200: Fix the taken-out TEM sample on a low-temperature sample stage, and stabilize the temperature of the sample at 233K by controlling the heating current intensity of the sample stage.

[0124] Step 300: Turn on the objective lens current of the transmitted electron and pass a suitable current to apply an external magnetic field with a strength of 919 Oe to the sample, so that the magnetic structure in the sample can be transformed.

[0125] Step 400: Record the end time of the transformation of the magnetic structure in the sample, which is 85 seconds.

[0126] Step 500 , turning off the objective lens current and simultaneously using laser heating with a laser beam radius of about 20 μm and a power of about 60 mW to demagnetize the sample, that is, to restore the magnetic structure to the initial state of the transformation.

[0127] like Figure 3 As shown, after recording a magnetic structure transition, the current in objective lens 5 is turned off, placing the thin sample in a zero-magnetic field environment. A laser beam 2 of sufficient energy is generated by a laser. After entering the sample chamber of the transmission electron microscope, the laser beam, under the action of reflector 1, irradiates the thin sample supported on the variable-temperature sample holder 6, rapidly raising the sample temperature to above 278K. After laser 2 is removed, the magnetic structure in the thin sample quickly returns to its state before the magnetic structure phase transition.

[0128] Step 600: By controlling the current of the variable temperature sample rod, the sample temperature is stabilized at 235 K, 237 K, and 240 K. After the sample temperature is stabilized, steps 300, 400, and 500 are repeated.

[0129] like Figure 4 As shown in the figure, the detailed dynamic process of the magnetic structure phase transition is recorded visually, and the time required for the magnetic structure phase transition to complete is accurately determined. (1) is the state before the magnetic structure phase transition, (2) is the state after the magnetic structure phase transition, and (3) is the sample temperature T as the horizontal axis and the corresponding magnetic phase transition completion time t f The vertical axis is the fitted relationship curve.

[0130] Figure 4 The magnetic state diagram before and after the completion of the magnetic structure phase transition in the FeGe alloy of Example 2 and the relationship curve between the sample temperature and the completion time of the magnetic phase transition are shown; wherein, Figure 4 (1) shows the magnetic state diagram before the magnetic structure phase transition is completed in FeGe alloy. Figure 4 (2) shows the magnetic state diagram after the magnetic structure phase transition in FeGe alloy is completed. Figure 4 (3) shows the relationship between sample temperature and magnetic phase transition completion time.

[0131] Step 700: The magnetic structure transition time t measured at different temperatures T is f , according to the Arrhenius formula t0 is the characteristic relaxation time, K b Fit the Boltzmann constant to obtain the activation energy barrier E of the magnetic structure phase transition in the sample to be tested. b Size and characteristic relaxation time t0. These include:

[0132] Step 701: Take the temperature T of the sample as the horizontal axis and the time t required for the corresponding magnetic phase change to complete. f As the vertical coordinate, draw a relationship curve;

[0133] Step 702: According to the Arrhenius formula, the temperature T and the time t f Perform fitting calculations on the data, and the Arrhenius formula is:

[0134] Where t0 is the characteristic relaxation time, K b is the Boltzmann constant, E b is the energy barrier for magnetic structure transition.

[0135] When T=232K, t f =85s;

[0136] When T=235K, t f =46s;

[0137] When T=237K, t f =24s;

[0138] When T=240K, t f =8s;

[0139] The four sets of experimental data were fitted nonlinearly according to the Arrhenius formula, and the specific value of t0 was obtained as 8.67×10 -30 s, E b The specific value is 2.29×10 -19 J.

[0140] Although the present invention has been described to a certain extent, it is obvious that appropriate changes in various aspects can be made without departing from the spirit and scope of the present invention. It is understood that the present invention is not limited to the embodiments described, but belongs to the scope of the claims, which includes equivalent replacements of each factor described.

Claims

1. A method for measuring the activation energy and characteristic relaxation time of a nanomagnetic structure phase transition process, characterized in that: The method comprises the following steps: (1) Preparation of nanometer-thick specimens suitable for transmission electron microscopy from bulk samples; (2) Fixing the sample prepared in step (1) on a temperature-variable sample rod, and setting the temperature T of the thin sample by adjusting the heating current; (3) Enabling the electron microscope objective lens in Lorentz working mode, applying a current intensity to it to generate the required external magnetic field to achieve the application of external magnetic fields of different intensities to the sample; (4) Record the time point t when the magnetic structure phase change in the sample is completed f ; (5) Turn off the electron microscope objective current, heat the sample to a temperature higher than the Curie temperature of the sample, and demagnetize the sample so that the magnetic structure returns to its initial state, thereby removing the hysteresis effect of the magnetic structure phase change process; (6) Repeat steps (2) to (5) to obtain the relaxation time required for the magnetic structure phase transition of the sample at different temperatures; (7) The magnetic structure transition time t measured at different temperatures T f , fitting according to the Arrhenius formula, and obtaining the activation energy and characteristic relaxation time of the thermodynamic process of magnetic structure phase transition in the sample.

2. The method according to claim 1, characterized in that In step (1), the thickness of the sample is 40 to 60 nm.

3. The method according to claim 2, characterized in that In step (1), the thickness of the sample is 50 to 55 nm.

4. The method according to claim 1, wherein In step (1), preparing a sample suitable for transmission electron microscopy observation from the bulk sample includes the following steps: (A) Polishing the surface of the bulk sample; (B) placing the sample processed in step (A) on a focused ion beam processing platform and performing deposition protection using a PtC precursor gas; (C) Dig a triangular groove longer than the protective layer on both sides of the protective layer; (D) The end surface close to the protective layer is continuously refined in the triangular groove to reduce the thickness of the sample under the protective layer by 500-600 nm; (E) Cutting the connection between the sample under the protective layer and the bulk sample, leaving only the supporting portion of the sample to be taken; (F) Using a robotic arm to insert the nanoprobe close to the sample to be taken, while introducing PtC precursor gas to allow the sample to be taken to adhere to the probe tip; (G) Cutting off all connections between the sample and the block, and transferring the sample to be taken to a dedicated sample stage of a transmission electron microscope using a nanoprobe; (H) The transferred sample is thinned to a thickness of less than 80 nm, which is enough for high-energy electron beams to penetrate.

5. The method according to claim 1, wherein In step (2), the temperature T is 100-400K.

6. The method according to claim 5, characterized in that In step (2), the temperature T is 100-250K.

7. The method according to claim 1, characterized in that In step (3), the current intensity is 0 to 0.65A.

8. The method according to claim 7, characterized in that In step (3), the current intensity is 0 to 0.5A.

9. The method according to claim 1, characterized in that In step (4), the time point t at which the magnetic structure phase change in the sample is completed is recorded. f The following steps are involved: (I) recording the magnetic contrast change information of the magnetic structure during the transformation process by recording image software; (II) The magnetic structure image after the objective lens current is turned on, which is regarded as the time zero of the magnetic structure transition; (III) Recording the image data of the completion process of the magnetic structure phase transition, and taking the time point when the magnetic structure no longer changes as the time required for the magnetic structure phase transition to complete t f .

10. The method according to claim 1, characterized in that In step (5), the method of heating the sample is pulsed or continuous laser irradiation.

11. The method according to claim 1, wherein In step (6), the repetition number is 4 to 8 times.

12. The method according to claim 11, characterized in that In step (6), the repetition number is 6 times.

13. The method according to any one of claims 1 to 12, characterized in that In step (7), the fitting method includes the following steps: (a) The temperature T of the sample is the horizontal axis, and the time t required for the corresponding phase change to complete is the horizontal axis. f As the vertical coordinate, draw a relationship curve; (b) According to the Arrhenius formula, the temperature T and time t f Perform fitting calculations on the data, and the Arrhenius formula is: , where t0 is the characteristic relaxation time, K b is the Boltzmann constant, E b is the energy barrier for magnetic structure transition.

14. A method for characterizing the magnetodynamic process and / or intrinsic magnetic properties of a magnetic material, characterized in that: The method comprises the method for measuring the activation energy and characteristic relaxation time of the phase transition process of the nanomagnetic structure according to any one of claims 1 to 13.

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