A thulium iron garnet film with adjustable magnetic anisotropy and surface roughness and a preparation method thereof

Abstract

The invention discloses a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness and a preparation method thereof, the preparation method comprising the following steps: placing a gadolinium gallium garnet substrate and a thulium iron garnet target in a cavity of a pulsed laser deposition device; after the cavity is evacuated, oxygen is introduced, and the oxygen pressure is adjusted to 10-30Pa; after heating, the laser is turned on and the laser energy is adjusted, and then the thulium iron garnet target is pre-bombarded by laser; after the pre-bombardment is completed, the thulium iron garnet target is bombarded again to grow a film on the gadolinium gallium garnet substrate; after the bombardment is completed, in-situ annealing is performed, and the thulium iron garnet film with adjustable magnetic anisotropy and surface roughness is obtained after the growth oxygen pressure is kept cooled to room temperature. The magnetic anisotropy and surface roughness of the thulium iron garnet film obtained by the present invention are adjustable, which provides the possibility for the further application of the thulium iron garnet film in spin electronics.

Description

Technical Field

[0001] The invention relates to the technical field of thin film materials, and in particular to a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness and a preparation method thereof. Background Art

[0002] Magnetic random access memory (MRAM) based on electron spin, especially the memory using spin transfer torque (STT) and spin-orbit torque (SOT), has become a new generation candidate memory due to its scalability, low power consumption and high speed. Moreover, SOT-MRAM has more advantages than STT-MRAM in comparison. First, the writing and reading of SOT-MRAM are separated, which can improve the stability of the device, reduce the operating power, and eliminate the undesirable errors in the bit reading and writing process. SOT-MRAM has great application potential as a non-volatile memory, especially a cache memory with high requirements for operation speed. In SOT-MRAM, SOT from the adjacent heavy metal layer (HM) can realize the magnetic flipping of the ferromagnetic layer (FM). Therefore, an HM layer with strong spin-orbit coupling (such as Pt, Ta or W) is required to improve the device efficiency. In particular, since SOT-MRAM does not require charge current to pass through the FM layer, magnetic insulating materials can be used instead of conductors to further reduce the power consumption of the device. Among many materials, rare earth ferromagnetic insulators (FMIs) are a good choice due to their large band gap, small magnetization damping and good thermal stability.

[0003] In the past few decades, yttrium iron garnet (Y3Fe5O 12 ) has attracted great attention in spin electronics. Due to its high transparency, extremely low magnetic damping and high-temperature durability, Y3Fe5O 12 It has potential application value in many fields such as spin wave communication and ultra-low power spin wave devices. A recent study has shown that Y3Fe5O 12 The current-induced magnetization switching of SOT has an in-plane magnetic easy axis. However, SOT requires FMI films with perpendicular magnetic anisotropy to fully utilize the spin current generated by current in FMI / NM heterostructures. 12 The film usually needs to be doped with elements such as Mn and Bi to make the film have ideal perpendicular magnetic anisotropy.

[0004] Thulium iron garnet (Tm3Fe5O 12 ) has high magnetoelasticity and negative magnetostriction coefficient, and is easier to achieve perpendicular magnetic anisotropy, making it an excellent FMI material. Tm3Fe5O with perpendicular magnetic anisotropy can be easily prepared by sputtering, pulsed laser deposition and crystallization. 12Thin films, such as the Chinese patent application document with publication number CN115968249A, discloses a method for preparing Tm3Fe5O by pulsed laser deposition technology. 12 Therefore, some experiments have demonstrated that SOT 12 Magnetization switching in heterostructures paves the way for the development of oxide-based ultra-low dissipation spintronics devices.

[0005] So, how to prepare and regulate Tm3Fe5O 12 The magnetic anisotropy of the film and its surface roughness become more important. Summary of the invention

[0006] The technical problem to be solved by the present invention is how to prepare a Tm3Fe5O3 with adjustable magnetic anisotropy and surface roughness. 12 film.

[0007] The present invention solves the above technical problems through the following technical means:

[0008] A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness comprises the following steps:

[0009] S1, placing a gadolinium gallium garnet substrate and a thulium iron garnet target in a cavity of a pulsed laser deposition device;

[0010] S2, evacuate the cavity and introduce oxygen, adjusting the oxygen pressure to 10-30Pa;

[0011] S3, after heating, turning on the laser and adjusting the laser energy, and then pre-bombarding the thulium iron garnet target with laser;

[0012] S4, after the pre-bombardment is completed, the thulium iron garnet target is bombarded again to grow a thin film on the gadolinium gallium garnet substrate;

[0013] S5. After the bombardment is completed, in-situ annealing is performed, and the growth oxygen pressure is maintained and the temperature is lowered to room temperature to obtain the thulium iron garnet film with adjustable magnetic anisotropy and surface roughness.

[0014] Preferably, in S1, before placing in the cavity, it also includes wiping the surface of the gadolinium gallium garnet substrate with dust-free paper; and smoothing the surface of the thulium iron garnet target with sandpaper.

[0015] Preferably, in S2, the vacuum is evacuated to 6.5e -4 Pa.

[0016] Preferably, in S2, the step of evacuating the cavity includes: closing the cavity, evacuating the cavity to 5 Pa with a mechanical pump, and then turning on the molecular pump to continue evacuating the cavity to 6.5e -4 Pa.

[0017] Preferably, in S3, after the temperature of the GdGaG substrate is raised to 750°C, the laser is turned on and the laser energy at the cavity light entrance is adjusted to 65 mJ.

[0018] Preferably, in S3, a substrate baffle is provided in the cavity, and the substrate baffle is opened to shield the gadolinium gallium garnet substrate during the laser pre-bombardment process; the pulse number of the laser pre-bombardment is 1000-7000, and the laser frequency is 10 Hz.

[0019] Preferably, in S3, the number of pulses of the laser pre-bombardment is 2000-5000.

[0020] Preferably, in S3, the number of pulses of the laser pre-bombardment is 2000-3000.

[0021] Preferably, in S5, the in-situ annealing time is 10 min.

[0022] Preferably, during the film growth process, the easy axis of magnetization of the film obtained by adjusting the oxygen pressure to 10-15 Pa is in-plane, and the easy axis of magnetization of the film obtained by adjusting the oxygen pressure to 20-30 Pa is out-of-plane.

[0023] The present invention also provides a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness, which is prepared by adopting the method for preparing the thulium iron garnet film with adjustable magnetic anisotropy and surface roughness.

[0024] The advantages of the present invention are:

[0025] Thulium iron garnet (Tm3Fe5O 12 ) is a ferromagnetic insulator. The present invention uses a pulsed laser deposition system (PLD) to prepare thulium iron garnet (Tm3Fe5O 12 ) film, by changing the oxygen pressure of the film growth and the number of laser pre-bombardment pulses, the magnetic anisotropy and surface roughness of the thulium iron garnet film can be controlled, which provides the possibility for the further application of thulium iron garnet film in spin electronics; specifically, the magnetic anisotropy of the film can be controlled by adjusting the oxygen pressure of the film growth, the number of laser pre-bombardment pulses can be controlled, and the magnetic anisotropy and surface roughness of the film can be controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Magnetic anisotropy energy diagrams of materials prepared with different numbers of pre-bombardment pulses in Examples 1-6 of the present invention;

[0027] Figure 2 It is an average height difference diagram of materials prepared with different numbers of pre-bombardment pulses in Examples 1-6 of the present invention;

[0028] Figure 3Magnetic anisotropy energy diagrams of materials prepared at different growth oxygen pressures in Examples 7-11 of the present invention;

[0029] Figure 4 The present invention is a flow chart of a method for preparing a thulium iron garnet film with controllable magnetic anisotropy and surface roughness. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0032] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0033] Example 1

[0034] Reference Figure 4 A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness comprises the following steps: 12 ) as the substrate, wipe the surface of the GdGaG substrate with dust-free paper, and use sandpaper to smooth the surface of the Thulium Iron Garnet (Tm3Fe5O 12 ) target surface, put the gadolinium gallium garnet substrate and the thulium iron garnet target into the chamber of the pulsed laser deposition system, close the chamber, and use a mechanical pump to evacuate to 5Pa. At this time, turn on the molecular pump to continue evacuating to 6.5e -4 Pa; Wait until the vacuum degree reaches 6.5e -4 When the temperature reaches 30 Pa, the molecular pump and the molecular pump valve are closed, the oxygen valve is opened, oxygen is introduced, and the mechanical pump is adjusted to pump by-pass to make the oxygen pressure in the cavity reach 30 Pa; the temperature is uniformly increased to a substrate temperature of 750°C; when the temperature is stable, the substrate baffle and the laser are opened, and the laser energy is measured at the cavity light entrance, and the energy is adjusted to 65mJ; the thulium iron garnet target is pre-bombarded, and the laser frequency during the pre-bombardment is 10Hz, and the number of laser pre-bombardment pulses is 1000; after the pre-bombardment, the substrate baffle is closed, the target is bombarded, and a thin film is grown on the substrate; after the growth is completed, in-situ annealing is performed for 10 minutes, and then the heating system is turned off to maintain the growth oxygen pressure, and when the temperature drops to room temperature, the film is taken out to obtain the thulium iron garnet film with adjustable magnetic anisotropy and surface roughness.

[0035] Example 2

[0036] A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness is similar to the method in Example 1, except that the number of laser pre-blast pulses is 1500.

[0037] Example 3

[0038] A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness is similar to the method in Example 1, except that the number of laser pre-blast pulses is 2000.

[0039] Example 4

[0040] A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness is similar to the method in Example 1, except that the number of laser pre-blast pulses is 3000.

[0041] Example 5

[0042] A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness is similar to the method in Example 1, except that the number of laser pre-blast pulses is 5000.

[0043] Example 6

[0044] A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness is similar to the method in Example 1, except that the number of laser pre-blast pulses is 7000.

[0045] The magnetic data of the films obtained with different laser pre-blast pulse numbers in Examples 1 to 6 were measured and the magnetic anisotropy energy was calculated. Specifically, the films were tested using VSM to obtain the hysteresis loop of the films, thereby obtaining the saturation field H s and saturation magnetic moment M s . The formula for calculating the effective magnetic anisotropy energy is: K eff =K σ +K s +K1 calculates the magnetic anisotropy energy K σ ; Among them, K eff : Effective magnetic anisotropy energy (K eff =H s ·M s / 2); K σ : Magnetic anisotropy energy; K s : Shape anisotropy energy (K s =2π·M s 2 ); K1: intrinsic magnetocrystalline anisotropy (very small and can be ignored).

[0046] Use AFM (atomic force microscope) to scan the surface of the film. The average height difference represents the flatness of the surface. The smaller the height difference, the flatter the surface.

[0047] The laser pre-bombardment pulse number, magnetic anisotropy energy and surface roughness were plotted. Figure 1 and Figure 2 As shown by Figure 1 and Figure 2 It can be seen that the anisotropic energy of the film is the largest when the number of laser pre-blast pulses is 3000, close to 11 kJ / m 3 , indicating that it has extremely strong perpendicular magnetic anisotropy; and the surface of the film is very flat, which is conducive to the preparation of heterojunction.

[0048] Example 7

[0049] A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness is similar to the method in Example 1, except that: the number of laser pre-blast pulses is 4000; oxygen is introduced, and the mechanical pump is adjusted to pump by-pass so that the oxygen pressure in the cavity reaches 10Pa.

[0050] Example 8

[0051] A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness is similar to the method in Example 7, except that oxygen is introduced and the mechanical pump is adjusted to pump the oxygen in the chamber to a pressure of 15 Pa.

[0052] Example 9

[0053] A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness is similar to the method in Example 7, except that oxygen is introduced and the mechanical pump is adjusted to pump the oxygen in the chamber to a pressure of 20 Pa.

[0054] Example 10

[0055] A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness is similar to the method in Example 7, except that oxygen is introduced and the mechanical pump is adjusted to pump the oxygen in the chamber to a pressure of 25 Pa.

[0056] Embodiment 11

[0057] A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness is similar to the method in Example 7, except that oxygen is introduced and the mechanical pump is adjusted to pump the oxygen in the chamber to a pressure of 30 Pa.

[0058] The magnetic data of the films obtained by different oxygen pressures in Examples 7-11 were measured by the above method, and the magnetic anisotropy energy was obtained by calculation. A curve diagram of the growth oxygen pressure and the magnetic anisotropy energy was drawn. The results are as follows: Figure 3 As shown, the magnetization easy axis directions of 10Pa and 15Pa are in-plane, and the magnetization easy axis directions of 20Pa, 25Pa, and 30Pa are out-of-plane, which is determined by Figure 3 It can be seen that the regulation of magnetic anisotropy is achieved by changing the growth oxygen pressure.

[0059] It can be seen from the above examples that the present invention adjusts the magnetic anisotropy and surface roughness of the film by changing the number of laser pre-blast pulses and the growth oxygen pressure, thereby preparing Tm3Fe5O 12 Thin films provide greater possibilities for further applications in spin electronics.

[0060] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness, characterized in that: The following steps are involved: S1, placing a gadolinium gallium garnet substrate and a thulium iron garnet target in a cavity of a pulsed laser deposition device; S2, evacuate the cavity and introduce oxygen, adjusting the oxygen pressure to 10-30Pa; S3, after heating, turn on the laser and adjust the laser energy at the cavity light entrance to 65mJ, and then perform laser pre-bombardment on the thulium iron garnet target; the number of pulses of the laser pre-bombardment is 1000-7000, and the laser frequency is 10Hz; S4, after the pre-bombardment is completed, the thulium iron garnet target is bombarded again to grow a thin film on the gadolinium gallium garnet substrate; S5. After the bombardment is completed, in-situ annealing is performed, and the growth oxygen pressure is maintained and the temperature is lowered to room temperature to obtain the thulium iron garnet film with adjustable magnetic anisotropy and surface roughness.

2. The method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness according to claim 1, characterized in that: In S1, before being placed in the chamber, the surface of the gadolinium gallium garnet substrate is wiped with dust-free paper; and the surface of the thulium iron garnet target is smoothed with sandpaper.

3. The method for preparing a thulium iron garnet film with controllable magnetic anisotropy and surface roughness according to claim 1, characterized in that: In S2, evacuate to 6.5e -4 Pa.

4. The method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness according to claim 1, characterized in that: In S2, the step of evacuating the cavity includes: closing the cavity, evacuating the cavity to 5Pa with a mechanical pump, and then turning on the molecular pump to continue evacuating the cavity to 6.5e -4 Pa.

5. The method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness according to claim 1, characterized in that: In S3, the temperature of the GdGaG substrate is raised to 750°C and then the laser is turned on.

6. The method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness according to claim 1, characterized in that: In S3, a substrate baffle is provided in the cavity, and the substrate baffle is opened to shield the gadolinium gallium garnet substrate during the laser pre-bombardment process.

7. The method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness according to claim 1, characterized in that: In S3, the number of pulses of the laser pre-bombardment is 2000-5000.

8. The method for preparing a thulium iron garnet film with adjustable magnetic anisotropy and surface roughness according to claim 1, characterized in that: In S5, the in-situ annealing time is 10 min.

9. The method for preparing a thulium iron garnet film with controllable magnetic anisotropy and surface roughness according to any one of claims 1 to 8, characterized in that: During the film growth process, the easy axis of magnetization of the film obtained by adjusting the oxygen pressure to 10-15Pa is in-plane, and the easy axis of magnetization of the film obtained by adjusting the oxygen pressure to 20-30Pa is out-of-plane.

10. A thulium iron garnet film with adjustable magnetic anisotropy and surface roughness, characterized in that: The thulium iron garnet film is prepared by the method for preparing a thulium iron garnet film with controllable magnetic anisotropy and surface roughness as described in any one of claims 1 to 9.

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