Method for regulating ferromagnetic film to excite spin wave through electric field

Abstract

The invention discloses a method for exciting spin waves by regulating and controlling a ferromagnetic film through an electric field, and belongs to the technical field of new materials of spintronics. By applying an electric field to generate strain in a ferromagnetic film surface, generation of magnetic anisotropy in the surface is induced, spin pinning conditions on the surface of the film are further changed, and finally controllable excitation of vertical static spin waves is achieved. By changing the magnitude of the applied voltage on the PMNPT ferroelectric substrate, electric control excitation of the vertical static spin wave (PSSW) is achieved, the method is simple and easy to implement, the regulation and control effect is remarkable, and the method is suitable for switch design of spin wave / magnetic vibrator devices and high-frequency microwave devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of new materials in spintronics, and relates to a method for electrically controlling the excitation of spin waves in ferromagnetic thin films. Background Art

[0002] Nowadays, high-frequency soft magnetic thin films can be found almost everywhere in daily life. For example, soft magnetic thin film materials are involved in devices such as sensors, laptop computers, information recording media, high-frequency transformers, and recording read / write heads.

[0003] For the application of magnetic thin films in high-frequency devices, due to the limitations of the saturation magnetization intensity and magnetic anisotropy field of the thin films, the tunable range of the resonance frequency of the ferromagnetic resonance mode is limited. In order to seek higher resonance frequencies, people have tried to explore ferromagnetic resonance modes different from coherent precession. The excitation and detection of spin waves are the main challenges in realizing magnonic device technology. In commercial applications, the excitation efficiency of spin waves determines the energy consumption and error rate of the devices.

[0004] Strain has a definite influence on the magnetic dynamics of magnetic thin films grown on flexible substrates. Nevertheless, the current research on using strain to control the magnetization dynamics of thin films is still in its infancy, and there is still a lot of work to be done regarding both the types of control effects on magnetization dynamics and its influencing laws and mechanisms.

[0005] From the currently reported research, the excitation conditions of spin waves are still quite harsh in terms of both material processes and the energy consumption required for external excitation. How to improve the excitation efficiency of spin waves remains a challenge. Developing new and effective spin wave excitation methods is of great significance for the development of the next generation of new high-frequency devices. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for controlling the excitation of spin waves in ferromagnetic thin films based on a PMNPT (lead magnesium niobate) ferroelectric substrate, aiming at the relationship between the control type of strain on magnetization dynamics and its influencing laws and mechanisms, with the guidance of developing new and effective spin wave excitation methods.

[0007] First, the present invention provides a method for electrically controlling the excitation of spin waves in ferromagnetic thin films. A ferroelectric material is used as the substrate, and a buffer layer, a magnetic layer, and an antioxidant coating layer are sequentially arranged on its first surface. Electrodes are respectively arranged on the second surface of the substrate and the surface of the antioxidant coating layer to obtain a ferromagnetic thin film structure capable of applying an electric field. A voltage of ±200 - 400 volts is applied between the two electrodes of the ferromagnetic thin film structure to generate strain inside the thin film, induce the generation of in-plane magnetic anisotropy, and then change the spin pinning conditions on the surface of the thin film, ultimately realizing the controllable excitation of perpendicular static spin waves.

[0008] Preferably, the position of the perpendicular static spin wave is regulated by changing the voltage direction (polarity) and magnitude, and the coercive force of the ferromagnetic thin film structure is regulated simultaneously.

[0009] Preferably, the magnetic layer is one of CoFeB, CoFeSi, and FeGa, and its thickness is 60-100 nm.

[0010] Preferably, the anti-oxidation coating layer is one of aluminum, titanium, and platinum, and its thickness is 2-5 nm.

[0011] Preferably, the buffer layer is one of tantalum, platinum, and copper, and its thickness is 2-5 nm.

[0012] Preferably, the ferroelectric material is PMNPT (lead magnesium niobate: lead titanate with an atomic ratio of 0.7:0.3).

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] (1) The present invention provides a new method for controllably exciting perpendicular static spin waves in a ferromagnetic thin film, which can achieve electric field control of spin wave excitation in the ferromagnetic thin film. Compared with other methods, it has the characteristics of higher controllability and multiple excitation regulation of a single thin film, effectively reducing thin film loss and increasing the service life of the device.

[0015] (2) The present invention has a high degree of matching with the existing thin film deposition process, is easy to operate and control, can reduce costs, has a wider range of applications, and is suitable for existing production practices. Description of the Drawings

[0016] Figure 1 It is the connection method between the thin film structure and its electrodes.

[0017] Figure 2 It is the XED test chart of the PMNPT substrate.

[0018] Figure 3 It is the ferromagnetic resonance test of the sample in Example 2 under different voltages.

[0019] Figure 4 It is the VSM test of the sample in Example 2 under different voltages.

[0020] Figure 5 It is the TRMOKE test of the sample in Example 2 under different voltages. Detailed Embodiments

[0021] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0022] Figure 1Schematic diagram of the method for electrically controlling the spin-wave excitation of ferromagnetic thin films described in the present invention. It can be seen that the thin film structure includes a PMNPT substrate, tantalum, CoFeB, and aluminum from bottom to top in sequence. Electrodes are provided on the lower surface of the PMNPT substrate and the upper surface of the aluminum.

[0023] Example 1

[0024] Preparation method of ferroelectric substrate soft magnetic thin film, comprising the following steps:

[0025] 1. Select PMNPT (commercially available, its XRD is as Figure 2 shown) as the substrate. The cleaning process of the substrate is as follows: Immerse the substrate in an acetone solution at 60 °C, place it in an ultrasonic oscillation cleaning instrument and wash for 2 min. Take out the substrate processed in the previous step and dry it to ensure the cleanliness of the substrate surface. It can be seen that the crystal orientation and composition are PMN:PT = 0.7:0.3. Figure 2 It can be seen that the crystal orientation and composition are PMN:PT = 0.7:0.3.

[0026] 2. Install high-purity (higher than 99.99%) Ta target, Co 40 Fe 40 B 20 target, and Al target at the corresponding target positions in a high-vacuum magnetron sputtering coating instrument;

[0027] 3. Put the substrate in step 1 into the vacuum chamber of the high-vacuum magnetron sputtering coating instrument to prepare Co 40 Fe 40 B 20 alloy thin film. The specific process is as follows:

[0028] (1) Under the condition that the background vacuum degree of the chamber is better than 1×10 -7 mTorr, introduce argon, and control the total gas flow rate at 10 - 40 sccm.

[0029] (2) When the air pressure is stable at 20 mTorr, turn on the sputtering power supply, and sputter the Ta target, Co 40 Fe 40 B 20 target, and Al target with DC powers of 10 W, 30 W, and 6 W respectively to initiate the glow of the targets.

[0030] (3) After the glow is stable, reduce the air pressure to 2 - 5 mTorr. At a working air pressure of 2 - 5 mTorr, open the baffle of the target, grow a 2-nm buffer layer of Ta, and grow an 80-nm magnetic layer of Co 40 Fe 40 B 20 on the basis of the buffer layer of Ta. On the magnetic layer of Co 40 Fe 40 B 20Grow a 2nm antioxidant layer of Al on the basis of

[0031] (4) During the growth of the thin film, keep the sample stage rotating uniformly at a constant speed, control the growth at room temperature. After reaching the preset growth time, turn off the sputtering power supply and the target baffle to obtain the ferromagnetic thin film material.

[0032] Example 2

[0033] The present invention provides a method for electrically controlling the excitation of vertical static spin waves in a soft magnetic thin film, including the following steps:

[0034] (1) At the bottom of the PMNPT substrate of the ferromagnetic thin film material obtained in the example and on the surface layer of the thin film, that is, the aluminum thin film, use silver glue to externally connect electrodes, and provide an electric field by externally connecting a Keithley 2410 voltmeter; wherein the Keithley 2410 can provide a voltage of ±0 - 600V.

[0035] (2) Pay attention to connecting the protection circuit when connecting the circuit. The protection circuit is configured as follows: connect a 10MΩ color ring resistor in series at each end of the voltmeter. When connecting the wires, use thin copper wires for the wires of the thin film and the substrate part to prevent stress shedding and avoid the influence of external stress at the same time. Use 0.3mm copper wires for the rest to facilitate fixing and the protection circuit.

[0036] (3) When testing with a vibrating sample magnetometer (VSM), pay attention to fixing the position of the thin film to prevent the wires from falling off when the vibrating rod vibrates; for the TRMOKE test, the connection position on the surface of the thin film is close to the corner, leaving enough space to select the laser point. Select a flat and smooth position for the laser point, and keep the selected position of the laser point consistent.

[0037] (4) Due to the relaxor property of the PMNPT ferroelectric substrate used in the experiment for ferromagnetic resonance testing, the stress retention time exceeds 30 minutes after applying pressure; therefore, it can be tested by washing the surface after applying voltage and making the thin film fit the coplanar waveguide, which is beneficial for measuring a stronger signal.

[0038] Figure 3 For the sample of Example 2, ferromagnetic resonance tests were carried out at 10 GHz frequency under 0V, 400V, and -400V respectively. It can be seen that under the condition of ±400V, in addition to the Kittle mode of coherent precession, vertical static spin waves (PSSW) appear; at the same time, under the condition of +400V, both wave peaks show a phenomenon of shifting towards a higher magnetic field.

[0039] Figure 4 For the vibrating sample magnetometer (VSM) diagrams of the sample of Example 2 under 0V, 400V, and -400V, it can be seen that under the condition of ±400V, changes in the coercivity occur, proving that the electric field can effectively regulate the coercivity of the ferromagnetic thin film.

[0040] Figure 5 Figure for the TRMOKE test of the sample in Example 2 at 0V, 400V, and -400V. By comparison, an obvious single PSSW appears in the -400V test, and two obvious PSSW signals appear under the condition of +400V. It can be seen that the electric field can effectively excite and regulate the vertical static spin wave, and can regulate the appearance of multiple waves.

[0041] The above embodiments are preferred embodiments of the present invention and are not used to limit the present invention. Any person familiar with this technology can make changes, modifications, substitutions, combinations, and simplifications to the above examples without departing from the spirit and principles of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention are included in the protection scope of the present invention.

Claims

1. A method for electrically controlling the excitation of spin waves in ferromagnetic thin films, characterized in that, using a ferroelectric material as a substrate, a buffer layer, a magnetic layer and an antioxidant coating are sequentially arranged on its first surface, electrodes are respectively arranged on the second surface of the substrate and the surface of the antioxidant coating to obtain a ferromagnetic thin film structure capable of applying an electric field, and a voltage of ±200 - 400 volts is applied between the two electrodes of the ferromagnetic thin film structure to generate strain inside the thin film, induce the generation of in-plane magnetic anisotropy, and further change the spin pinning conditions on the thin film surface to achieve controllable excitation of perpendicular static spin waves.

2. The method according to claim 1, characterized in that, the position of the perpendicular static spin wave is controlled by changing the direction and magnitude of the voltage, and at the same time, the coercivity of the ferromagnetic thin film structure is controlled.

3. The method according to claim 1, characterized in that, the magnetic layer is one of CoFeB, CoFeSi, FeGa, and its thickness is 60 - 100 nm.

4. The method according to claim 1, characterized in that, the antioxidant coating is one of aluminum, titanium, platinum, and its thickness is 2 - 5 nm.

5. The method according to claim 1, characterized in that, the buffer layer is one of tantalum, platinum, copper, and its thickness is 2 - 5 nm.

6. The method according to claim 1, characterized in that, the ferroelectric material is lead magnesium niobate, wherein the atomic ratio of lead magnesium niobate to lead titanate is 0.7:0.3.

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