Method for efficient phase separation and magnetic property enhancement of antispinel NiCo2O4 film

Abstract

The invention provides a method for efficient phase separation and magnetic property enhancement of an antispinel NiCo2O4 film. The method comprises the following steps: (1) preparing the antispinel NiCo2O4 film on a single crystal substrate through a pulse laser deposition technology; and (2) growing an ultrathin covering layer with strong oxygen affinity on the surface of the anti-spinel NiCo2O4 film, wherein the thickness of the covering layer film is 1-100nm. According to the invention, the covering layer film with strong oxygen affinity characteristic is grown on the antispinel NiCo2O4 film, oxygen vacancies in the antispinel NiCo2O4 film are induced to efficiently migrate to the covering layer, and a second phase with excellent magnetic property is formed in the antispinel NiCo2O4 film, so that the magnetic property of the antispinel NiCo2O4 film is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of material technology applications, and particularly to a method for improving phase separation and magnetic enhancement of NiCo2O4 thin films. Background Art

[0002] Transition metal oxides can exhibit a series of novel physical phenomena due to their rich degrees of freedom and strong mutual coupling effects. At the same time, the relatively high perpendicular magnetic anisotropy of transition metal oxides is required for applications in spintronic devices. Among many transition metal oxide conductors, ferromagnetic materials, especially those with perpendicular magnetic anisotropy, are scarce.

[0003] Inverse spinel AB2O4 materials have been widely used in optoelectronic detection, electrocatalysis, supercapacitors, magnetic storage, magnetic sensing detection devices, etc. due to their excellent properties such as high electrochemical activity, conductivity, and magnetocrystalline anisotropy. Among them, the inverse spinel structure NiCo2O4 is a ferrimagnetic metal material and exhibits significant perpendicular magnetic anisotropy, showing great potential in the applications of spintronic devices and radio frequency communication. However, the highest value of the Curie temperature (paramagnetic transition temperature, T C ) of the current NCO thin film is only 395K, which severely limits its practical applications in high-temperature scenarios.

[0004] The spin magnetic moment of the NiCo2O4 thin film mainly comes from Co in the tetrahedron and Ni in the octahedron. Therefore, the valence state distribution of cations has a greater impact on the magnetism of the thin film. However, the cation occupation and valence state distribution in inverse spinel oxides are complex, and there are certain limitations in regulating metal cations. Therefore, the crystal structure and magnetic properties are generally effectively regulated by non-metal ions. The precipitation of the second phase in the inverse spinel NiCo2O4 thin film can significantly improve the magnetic properties of the NiCo2O4 thin film. The present invention utilizes the formation of oxygen vacancy energy and migration energy mismatch between the NiCo2O4 thin film and the oxygen-deficient ultrathin capping layer, and grows an oxygen-deficient ultrathin capping layer (such as: SrTiO 3-δ , TiO 2-δ ) or a metal capping layer on the inverse spinel NiCo2O4 thin film to construct a heterostructure, inducing oxygen ions to migrate from the inverse spinel NiCo2O4 thin film to the capping layer and oxygen vacancies to migrate from the surface capping layer to the NiCo2O4 thin film, realizing the phase separation of the inverse spinel NiCo2O4 thin film and the improvement of the magnetic properties of the thin film. This method not only effectively improves the ultra-high vacuum conditions required for the phase separation of the NiCo2O4 thin film but also realizes the coexistence characteristics of high-temperature magnetism and insulation. Summary of the Invention

[0005] In the present invention, a thin film covering layer is grown on the surface of the inverse spinel NiCo2O4 thin film, inducing oxygen ions to migrate from the inverse spinel NiCo2O4 thin film to the covering layer, and inducing oxygen vacancies to migrate from the surface covering layer to the inverse spinel NiCo2O4 thin film, so that a second phase appears in the inverse spinel NiCo2O4 thin film, and the Curie temperature and saturation magnetization intensity of the thin film are increased.

[0006] To solve the above problems, the present invention proposes the following technical solutions:

[0007] Provided is a method for efficient phase separation and enhancement of magnetic properties of an inverse spinel NiCo2O4 thin film, comprising the following steps:

[0008] (1) Prepare an inverse spinel NiCo2O4 thin film on a substrate by pulsed laser deposition technology, with a preparation temperature of 350 - 700 °C and a deposition oxygen pressure of 0.01 - 20 Pa, to obtain an inverse spinel NiCo2O4 thin film, and the thickness of the inverse spinel NiCo2O4 thin film is 2 - 100 nm;

[0009] (2) Then grow a covering layer thin film on the surface of the inverse spinel NiCo2O4 thin film, inducing oxygen ions to migrate from the inverse spinel NiCo2O4 thin film to the covering layer thin film, and inducing oxygen vacancies to migrate from the covering layer thin film to the inverse spinel NiCo2O4 thin film. Phase separation occurs in the inverse spinel NiCo2O4 thin film, and a second phase appears, finally forming a NiCo2O4 / covering layer heterojunction, and the structure changes to a heterojunction structure. The thickness of the covering layer thin film is 1 - 100 nm, the growth temperature is 350 - 800 °C, and the deposition oxygen pressure is < 10 -1 Pa.

[0010] Further, in the step (1), the heat preservation time of the inverse spinel NiCo2O4 thin film is 0 - 20 min.

[0011] Further, the laser light source of the pulsed laser deposition technology is a KrF excimer laser, with a wavelength of 248 nm, a laser pulse width of 10 ns, a laser energy density of 2.6 J / cm 2 , and a laser frequency of 1 - 10 Hz.

[0012] Further, the substrate is a MgAl2O4 single crystal substrate with a <001> crystal plane orientation, and the lattice constant of the MgAl2O4 single crystal substrate is

[0013] Further, the covering layer thin film is one of oxygen-deficient perovskite oxides, simple oxides, and easily oxidized metal elemental materials.

[0014] Further, the perovskite oxide is SrTiO3-δ , one of LaAlO 3-δ in the simple oxide thin film coating is TiO 3-δ , Al2O 3-δ in the easy-to-oxidize metallic elemental material is one of Al, Ti, Ag, and Cu.

[0015] Furthermore, the position of the XRD diffraction peak of the second phase is 51.8° - 52°, indicating that the spinel NiCo2O4 thin film after the coating has undergone a structural phase transition and its magnetism has changed to ferromagnetic.

[0016] Furthermore, the saturation magnetization intensity of the NiCo2O4 / coating heterojunction is 100 - 1000 emu / cc.

[0017] The method for efficient phase separation and enhanced magnetic properties of the spinel NiCo2O4 thin film provided by the present invention has the following beneficial effects:

[0018] By growing a metal coating thin film on the surface of the spinel NiCo2O4 thin film in the present invention, it induces oxygen ions to migrate from the spinel NiCo2O4 thin film to the coating, and oxygen vacancies migrate from the surface coating to the NiCo2O4 thin film, thereby causing a second phase to appear in the spinel NiCo2O4 thin film and forming a NiCo2O4 / coating heterojunction, which improves the Curie temperature and saturation magnetization intensity of the spinel NiCo2O4 thin film. Description of the Drawings

[0019] Figure 1 is a comparison chart of the XRD test results of Examples 2 - 5 and Comparative Examples 1 - 2 of the present invention;

[0020] Figure 2 is a comparison chart of the magnetic hysteresis loop results of Examples 2 - 5 and Comparative Examples 1 - 2 of the present invention at 10K;

[0021] Figure 3 is a comparison chart of the magnetic hysteresis loop results of all Examples 2 - 5 and Comparative Example 1 of the present invention at 400K;

[0022] Figure 4 is the XRD test result chart of Example 5 of the present invention. Detailed Embodiments

[0023] Next, the technical solutions in the embodiments will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments to be described below are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0024] Example 1

[0025] Provide a method for efficient phase separation and enhanced magnetic properties of inverse spinel NiCo2O4 thin films, including the following steps:

[0026] (1) Select a MgAl2O4 (abbreviated as MAO, the same below) single crystal substrate with a crystal plane orientation of <001>, and the lattice constant is Using pulsed laser deposition technology, the laser source is a KrF excimer laser with a wavelength of 248 nm, a laser pulse width of 10 ns, and a laser energy density of 2.6 J / cm 2 , the laser frequency is 10 Hz, and under the growth conditions of 350 °C and 20 Pa, bombard the NiCo2O4 (abbreviated as NCO, the same below) target on the MAO single crystal substrate to prepare an NCO thin film, obtaining an inverse spinel NiCo2O4 thin film with a thickness of 100 nm. After holding for 20 min.

[0027] (2) After holding, grow a SrTiO 3-δ (STO 3-δ ) capping layer thin film on the surface of the inverse spinel NiCo2O4 thin film, the growth temperature is 350 °C, the oxygen pressure is 10 -4 Pa, and the STO 3-δ capping layer thin film is 100 nm, obtaining a NiCo2O4 / SrTiO 3-δ heterojunction (abbreviated as NCO / STO 3-δ heterojunction, the same below).

[0028] Perform XRD testing on the NCO / STO 3-δ heterojunction. The NCO thin film has two XRD diffraction peaks at the same time, showing a phase separation phenomenon, and the magnetism of the inverse spinel NiCo2O4 thin film is also improved.

[0029] Example 2

[0030] (1) Select a MAO single crystal substrate with a crystal plane orientation of <001>, and the lattice constant is Using pulsed laser deposition technology, the laser source is a KrF excimer laser with a wavelength of 248 nm, a laser pulse width of 10 ns, and a laser energy density of 2.6 J / cm 2 , the laser frequency is 3 Hz, and under the growth conditions of 350 °C and 20 Pa, bombard the NCO target on the MAO single crystal substrate to prepare an NCO thin film, obtaining an inverse spinel NiCo2O4 thin film with a thickness of 25 nm. After holding for 10 min.

[0031] (2) After holding, grow a STO 3-δ capping layer thin film on the surface of the inverse spinel NiCo2O4 thin film, the growth temperature is 600 °C, the oxygen pressure is 0.01 Pa, and the STO3-δ The overlay film is 15 nm, resulting in NCO / STO 3-δ heterojunction.

[0032] For the NCO / STO 3-δ heterojunction, XRD tests were carried out, and the results are as Figure 1 (b) shows that there are two XRD diffraction peaks in the NCO film at the same time, indicating phase separation. The XRD diffraction peak of the NCO film is located at 52°. The magnetic hysteresis loop (M–H curve) at 10 K is as Figure 2 (b) shows that the saturation magnetization at 10 K is 181 emu / cc, and the magnetic hysteresis loop (M–H curve) at 400 K is as Figure 3 (b) shows that the saturation magnetization at 400 K is 178 emu / cc.

[0033] Comparative Example 1

[0034] An MAO single crystal substrate with a crystal plane orientation of <001> was selected, and the lattice constant is Using pulsed laser deposition technology, the laser source is a KrF excimer laser with a wavelength of 248 nm, a laser pulse width of 10 ns, and a laser energy density of 1.0 J / cm 2 , the laser frequency is 3 Hz. Under the growth conditions of 350 °C and 20 Pa, an NCO film with a thickness of 25 nm was prepared by bombarding the NCO target on the MAO single crystal substrate. According to Figure 1 (a), the XRD results show that the XRD diffraction peak of the NCO film is located at 44°, and no phase separation occurs.

[0035] The corresponding magnetic properties of Comparative Example 1 were tested, and the magnetic hysteresis loops (M–H curves) at 10 K and 400 K were tested. The results are as Figure 2 (a) and Figure 3 (a) show that the NCO film without an overlay in Comparative Example 1 was 51 emu / cc at 10 K and had a magnetic property of 5 emu / cc at 400 K, and the magnetic properties did not increase.

[0036] Comparative Example 2

[0037] The NCO film obtained in Comparative Example 1 was annealed for 30 min in a 10 -4 Pa vacuum environment. The XRD results after annealing are as Figure 1 (f) shows that there is no diffraction peak at 52° of the second phase in its XRD pattern. The corresponding magnetic properties were tested, and the result of the magnetic hysteresis loop (M–H curve) at 10 K is as Figure 2 (f) shows 10 emu / cc; the result of the magnetic hysteresis loop (M–H curve) at 400 K is as Figure 3(f) shows 0 emu / cc, with poor results.

[0038] Therefore, to improve the magnetic properties of the NCO thin film, a capping layer thin film needs to be grown.

[0039] Example 3

[0040] Provide a method for efficient phase separation and enhanced magnetic properties of inverse spinel NiCo2O4 thin films, including the following steps:

[0041] (1) Select a MAO single crystal substrate with a <001> crystal plane orientation and a lattice constant of Using pulsed laser deposition technology, the laser source is a KrF excimer laser with a wavelength of 248 nm, a laser pulse width of 10 ns, and a laser energy density of 2.6 J / cm 2 , the laser frequency is 1 Hz, and under the growth conditions of 700 °C and 0.01 Pa, bombard NCO on the MAO single crystal substrate, and prepare an NCO thin film with a target material to obtain an inverse spinel NiCo2O4 thin film with a thickness of 2 nm without heat preservation.

[0042] (2) Then grow an STO 3-δ capping layer thin film on the surface of the inverse spinel NiCo2O4 thin film. The growth temperature is 800 °C, the oxygen pressure is 0.01 Pa, and the STO 3-δ capping layer thin film is 2 nm to obtain an NCO / STO 3-δ heterojunction.

[0043] As Figure 1 (c) shows, perform XRD testing on the NCO / STO 3-δ heterojunction. The NCO thin film has two XRD diffraction peaks at the same time. The XRD diffraction peak of the NCO thin film is located at 52°. As Figure 2 (c) shows, test the hysteresis loop (M–H curve) at 10 K. The saturation magnetization at 10 K is 430 emu / cc; as Figure 3 (c) shows, the hysteresis loop (M–H curve) at 400 K, and the saturation magnetization is 410 emu / cc.

[0044] Example 4

[0045] Provide a method for efficient phase separation and enhanced magnetic properties of inverse spinel NiCo2O4 thin films, including the following steps:

[0046] (1) Select a MAO single crystal substrate with a <001> crystal plane orientation and a lattice constant of Using pulsed laser deposition technology, the laser source is a KrF excimer laser with a wavelength of 248 nm, a laser pulse width of 10 ns, and a laser energy density of 2.6 J / cm 2, the laser frequency is 3 Hz. Under the growth conditions of 600 °C and 0.05 Pa, NCO is bombarded on the MAO single crystal substrate to prepare an NCO thin film, and an inverse spinel NiCo2O4 thin film with a thickness of 2 nm is obtained, and the temperature is kept for 10 min.

[0047] (2) After the heat preservation is completed, STO 3-δ coating film is grown on the surface of the inverse spinel NiCo2O4 thin film. The growth temperature is 600 °C, and the oxygen pressure is 10 -3 Pa. The STO 3-δ coating film is 1 nm, and an NCO / STO 3-δ heterojunction is obtained.

[0048] As Figure 1 (d) shows, XRD test is carried out on the NCO / STO 3-δ heterojunction. There are two XRD diffraction peaks in the NCO thin film at the same time. The XRD diffraction peak of the NCO thin film is located at 52°. As Figure 2 (d) shows, the hysteresis loop (M–H curve) is tested at 10 K, and the saturation magnetization intensity at 10 K is 628 emu / cc; as Figure 3 (e) shows, the hysteresis loop (M–H curve) at 400 K, and the saturation magnetization intensity is 600 emu / cc.

[0049] Example 5

[0050] Replace the coating film in Example 2 with one of the binary oxide TiO 2-δ and the metal Ti coating film. XRD tests are carried out on the NCO / Ti and NCO / TiO2 heterojunctions respectively. The results are as Figure 4 shown. Both the Ti metal coating layer and the binary oxide TiO2 coating layer can induce the appearance of a second phase in the thin film.

[0051] As Figure 1 (e) shows, XRD tests are carried out on the NCO / Ti and NCO / TiO2 heterojunctions respectively. There are two XRD diffraction peaks in the NCO thin film. The XRD diffraction peaks of the NCO thin film are both located at 51.9°. As Figure 2 (e) shows, the hysteresis loop (M–H curve) is tested at 10 K, and the saturation magnetization intensity at 10 K is 850 emu / cc; as Figure 3 (e) shows, the hysteresis loop (M–H curve) at 400 K, and the saturation magnetization intensity is 845 emu / cc.

[0052] In the above embodiments, the descriptions of each embodiment have their own emphases. For the parts not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0053] As described above, the above are the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for efficiently enhancing phase separation and magnetic properties of inverse spinel NiCo2O4 thin films, characterized in that: It includes the following steps: (1) Prepare a spinel NiCo2O4 thin film on a substrate by pulsed laser deposition technology. The preparation temperature is 350 - 700 °C, and the deposition oxygen pressure is 0.01 - 20 Pa to obtain a spinel NiCo2O4 thin film. The thickness of the spinel NiCo2O4 thin film is 2 - 100 nm; (2) Then, a covering layer film is grown on the surface of the inverse spinel NiCo2O4 film to induce the migration of oxygen ions from the inverse spinel NiCo2O4 film to the covering layer film, and the migration of oxygen vacancies from the covering layer film to the inverse spinel NiCo2O4 film. Phase separation occurs in the inverse spinel NiCo2O4 film, and a second phase appears, finally forming a NiCo2O4 / covering layer heterojunction. The thickness of the covering layer film is 1 - 100 nm, the growth temperature is 350 - 800 °C, and the deposition oxygen pressure is < 10 -1 Pa.

2. The method for efficiently enhancing the phase separation and magnetic properties of the inverse spinel NiCo2O4 thin film according to claim 1, characterized in that: In the step (1), the heat preservation time of the spinel NiCo2O4 thin film is 0 - 20 min.

3. The method for efficiently enhancing phase separation and magnetic properties of the inverse spinel NiCo2O4 thin film according to claim 1, characterized in that: The laser source of the pulsed laser deposition technology is a KrF excimer laser, with a wavelength of 248 nm, a laser pulse width of 10 ns, and a laser energy density of 2.6 J / cm 2 , and the laser frequency is 1 - 10 Hz.

4. The method for efficiently enhancing phase separation and magnetic properties of the inverse spinel NiCo2O4 thin film according to claim 1, characterized in that: The substrate is a MgAl2O4 single crystal substrate with a crystal plane orientation of <001>, and the lattice constant of the MgAl2O4 single crystal substrate is 5. The method for efficiently enhancing phase separation and magnetic properties of the inverse spinel NiCo2O4 thin film according to claim 1, characterized in that: The covering layer thin film is one of oxygen-deficient perovskite oxides, simple oxides, and easily oxidized metal elemental materials.

6. The method for efficiently enhancing phase separation and magnetic properties of the inverse spinel NiCo2O4 thin film according to claim 5, characterized in that: The perovskite oxide is one of SrTiO 3-δ , LaAlO 3-δ . The simple oxide thin film coating is one of TiO 3-δ , Al2O 3-δ . The easily oxidized metallic elemental material is one of Al, Ti, Ag, and Cu.

7. The method for efficiently enhancing the phase separation and magnetic properties of the inverse spinel NiCo2O4 thin film according to claim 1, characterized in that: The XRD diffraction peak position of the second phase is 51.8° - 52°, and the magnetic transition is ferromagnetic.

8. The method for enhancing the efficient phase separation and magnetic properties of the inverse spinel NiCo2O4 thin film according to any one of claims 1-7, characterized in that: The saturation magnetization intensity of the NiCo2O4 / covering layer heterojunction is 100 - 1000 emu / cc.

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