Method for enhancing perpendicular magnetic anisotropy of CoFe-based magnetic multilayer films

Abstract

The present invention discloses a method for enhancing the perpendicular magnetic anisotropy of a CoFe-based magnetic multilayer film. The specific steps are as follows: Step 1. Preparation of an MgO layer: Depositing the layer directly on a substrate by radio frequency magnetron sputtering; Step 2. Preparation of a CoFe-based magnetic layer: Depositing the CoFe-based magnetic layer on the MgO layer by radio frequency magnetron sputtering; Step 3. Preparation of a Mo isolation layer: Depositing the Mo isolation layer on the CoFe-based magnetic layer by direct current magnetron sputtering; Step 4. Preparation of a heavy metal layer: Depositing the heavy metal layer on the Mo isolation layer by direct current magnetron sputtering; Step 5. Annealing: After the heavy metal layer is deposited, the sample is annealed. This method has a simple preparation process, is relatively easy to prepare, and is effective and reliable for enhancing the perpendicular magnetic anisotropy of CoFe-based magnetic multilayer films.

Description

Technical Field

[0001] The invention belongs to the technical field of ferromagnetic metal thin film materials, and particularly relates to a method for enhancing the perpendicular magnetic anisotropy of a CoFe-based magnetic multilayer film. Background Art

[0002] Magnetic anisotropy is a fundamental physical property of ferromagnetic materials. It refers to the phenomenon in which a material's magnetic properties vary with direction. Specifically, this is manifested by the magnetic susceptibility, magnetization curve, hysteresis loop, and other properties of a magnetic material exhibiting different properties depending on the magnetization direction. In thin-film materials, the easy magnetization direction is perpendicular to the film surface. Films exhibiting this property are said to exhibit perpendicular magnetic anisotropy. With the trend toward miniaturization of electronic devices, the demand for high-density magnetic storage media is increasing. Using thin-film materials with perpendicular magnetic anisotropy as recording media is one effective means of increasing storage density. CoFe-based magnetic multilayers have attracted considerable research attention due to their ease of inducing perpendicular magnetic anisotropy. Existing techniques can enhance the perpendicular magnetic anisotropy of the system by reducing the thickness of the CoFe-based magnetic layer and by repeating the interfaces between the CoFe-based magnetic layer / oxide layer or the CoFe-based magnetic layer / non-magnetic metal layer. However, these methods are complex and challenging to prepare. Therefore, effectively enhancing the perpendicular magnetic anisotropy of CoFe-based magnetic multilayers has become a hot topic of research. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for enhancing the perpendicular magnetic anisotropy of a CoFe-based magnetic multilayer film. The method has a simple preparation process and is relatively easy to prepare, and is effective and reliable in enhancing the perpendicular magnetic anisotropy of the CoFe-based magnetic multilayer film.

[0004] The technical solution adopted by the present invention is a method for enhancing the perpendicular magnetic anisotropy of a CoFe-based magnetic multilayer film, and the specific steps are as follows:

[0005] Step 1. Preparation of MgO layer: Depositing directly on the substrate by radio frequency magnetron sputtering;

[0006] Step 2. Preparation of CoFe-based magnetic layer: depositing a CoFe-based magnetic layer on the MgO layer by radio frequency magnetron sputtering;

[0007] Step 3. Preparing a Mo isolation layer: depositing a Mo isolation layer on the CoFe-based magnetic layer by DC magnetron sputtering;

[0008] Step 4. Preparing a heavy metal layer: depositing a heavy metal layer on the Mo isolation layer by DC magnetron sputtering;

[0009] Step 5. Annealing: After the heavy metal layer deposition is completed, the sample is annealed.

[0010] The present invention is also characterized in that:

[0011] In step 1, the substrate is a Si substrate, a SiO substrate or a Si substrate with a pre-printed pattern.

[0012] The sputtering atmosphere is argon gas, and the argon gas flow rate is 18 sccm-36 sccm.

[0013] The substrate rotation speed of the magnetron sputtering system is 5rpm-20rpm.

[0014] In step 4, the material used for the deposited heavy metal layer is a material with a surface free energy higher than 2939mJ / m 2 It is composed of one or more non-ferromagnetic heavy metals such as Ta, W, Hf, etc. in any atomic ratio.

[0015] In step 5, the annealing temperature is 300° C.-500° C., and the annealing time is 1 hour.

[0016] The thickness of the MgO layer is 1 nm to 2 nm; the thickness of the CoFe-based magnetic layer is 1 nm to 1.7 nm; the thickness of the Mo isolation layer is 1 nm to 4 nm; and the thickness of the heavy metal layer is 2 nm to 5 nm.

[0017] The beneficial effects of the present invention are:

[0018] The present method increases the perpendicular magnetic anisotropy of CoFe-based magnetic multilayer films without reducing the thickness of the CoFe-based magnetic layer or introducing an additional periodic structure. Compared to the two methods of reducing the thickness of the CoFe-based magnetic layer and increasing the interface between the CoFe-based magnetic layer / oxide layer or the CoFe-based magnetic layer / non-magnetic metal layer, the present method achieves enhanced perpendicular magnetic anisotropy through elemental segregation in the CoFe-based alloy layer, offering the advantage of reduced preparation difficulty. Furthermore, the present method significantly enhances the thermal stability of the perpendicular magnetic anisotropy in CoFe-based magnetic multilayer films. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the CoFe-based magnetic multilayer film prepared by the method of the present invention;

[0020] Figure 2 is the in-plane and out-of-plane hysteresis loop of the MgO / CoFeB / Mo / W multilayer film obtained in Example 1;

[0021] Figure 3 is the in-plane and out-of-plane hysteresis loop of the MgO / CoFeB / W multilayer film obtained in Comparative Example 1;

[0022] Figure 4 1 is the in-plane and out-of-plane hysteresis loop of the MgO / CoFeB / Mo / W multilayer film obtained in Example 2;

[0023] Figure 5 is the in-plane and out-of-plane hysteresis loop of the MgO / CoFeB / W multilayer film obtained in Comparative Example 2;

[0024] Figure 6 1 is the in-plane and out-of-plane hysteresis loop of the MgO / CoFeB / Mo / W multilayer film obtained in Example 3;

[0025] Figure 7 These are the in-plane and out-of-plane hysteresis loops of the MgO / CoFeB / W multilayer film obtained in Comparative Example 3.

[0026] In the figure, 1. substrate, 2. MgO layer, 3. CoFe-based magnetic layer, 4. Mo isolation layer, 5. heavy metal layer. DETAILED DESCRIPTION

[0027] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] The present invention provides a method for enhancing the perpendicular magnetic anisotropy of a CoFe-based magnetic multilayer film. All film layers are grown using magnetron sputtering technology. The sputtering atmosphere is argon gas with an argon gas flow rate of 18 sccm-36 sccm. The substrate rotation speed of the magnetron sputtering system is 5 rpm-20 rpm.

[0029] The specific steps are as follows:

[0030] Step 1. Preparation of MgO layer 2: Deposition directly on substrate 1 by radio frequency magnetron sputtering;

[0031] In step 1, the substrate is a Si substrate, a SiO substrate or a Si substrate with a pre-printed pattern.

[0032] Step 2. Preparing a CoFe-based magnetic layer 3: depositing a CoFe-based magnetic layer 3 on the MgO layer 2 by radio frequency magnetron sputtering; the CoFe-based magnetic layer is an alloy material containing both Co and Fe.

[0033] Step 3. Preparing a Mo isolation layer 4: depositing a Mo isolation layer 4 on the CoFe-based magnetic layer 3 by a DC magnetron sputtering method;

[0034] Step 4. Preparing a heavy metal layer 5: depositing a heavy metal layer 5 on the Mo isolation layer 4 by DC magnetron sputtering;

[0035] In step 4, the material used for the deposited heavy metal layer 5 is a material with a surface free energy higher than 2939mJ / m 2 It is composed of one or more non-ferromagnetic heavy metals such as Ta, W, Hf, etc. in any atomic ratio.

[0036] Step 5. Annealing: After the heavy metal layer 5 is deposited, the sample is annealed. The sample structure is as follows: Figure 1 As shown, it includes a substrate 1, an MgO layer 2, a CoFe-based magnetic layer 3, a Mo isolation layer 4 and a heavy metal layer 5 arranged in sequence from top to bottom.

[0037] In step 5, the annealing temperature is 300° C.-500° C., and the annealing time is 1 hour.

[0038] In the prepared sample, the thickness of the MgO layer 2 is 1 nm to 2 nm; the thickness of the CoFe-based magnetic layer 3 is 1 nm to 1.7 nm; the thickness of the Mo isolation layer 4 is 1 nm to 4 nm; and the thickness of the heavy metal layer 5 is 2 nm to 5 nm.

[0039] The specifications of the instruments used in the following examples and comparative examples are as follows:

[0040] Magnetron sputtering system: brand Kurt J.Lesker, model PVD 75Proline.

[0041] Vibrating sample magnetometer: brand Microsense, model VSM-EZ9.

[0042] Vacuum annealing furnace: brand: Oriental Chenjing, model: high temperature magnetic field heating furnace.

[0043] Reagents: MgO, Co 40 Fe 40 B 20 (hereinafter referred to as CoFeB), Mo, and W targets were purchased from Zhongnuo New Materials (Beijing) Technology Co., Ltd.

[0044] Example 1:

[0045] The film thicknesses in this embodiment are all nominal film thicknesses, the deposition temperatures are all room temperature, the sputtering atmosphere is argon, the argon flow rate is 23 sccm, and the substrate rotation speed of the magnetron sputtering system is 10 rpm.

[0046] The steps of the method for enhancing the perpendicular magnetic anisotropy of the CoFe-based magnetic multilayer film are as follows:

[0047] Step 1: A 1 nm thick MgO layer was directly deposited on a Si substrate by radio frequency magnetron sputtering.

[0048] Step 2: A CoFeB layer with a thickness of 1.4 nm is deposited on the MgO layer by radio frequency magnetron sputtering.

[0049] Step 3: A Mo layer with a thickness of 2 nm is deposited on the CoFeB layer by DC magnetron sputtering.

[0050] Step 4: A W layer with a thickness of 4 nm is deposited on the Mo layer by DC magnetron sputtering.

[0051] Step 5: Place the sample obtained in step 4 in a vacuum annealing furnace for ex-situ annealing at a temperature of 400°C for 1 h.

[0052] Figure 2 Shown are the in-plane and out-of-plane hysteresis loops of MgO / CoFeB / Mo / W annealed at 400°C for 1 h.

[0053] Comparative Example 1:

[0054] The steps of this comparative example are basically the same as those of Example 1, except that a Mo isolation layer is added to the sample of Example 1.

[0055] The preparation steps of the CoFe-based magnetic multilayer film are as follows:

[0056] Step 1: A 1 nm thick MgO layer was directly deposited on a Si substrate by radio frequency magnetron sputtering.

[0057] Step 2: A CoFeB layer with a thickness of 1.4 nm is deposited on the MgO layer by radio frequency magnetron sputtering.

[0058] Step 3: A W layer with a thickness of 4 nm is deposited on the CoFeB layer by DC magnetron sputtering.

[0059] Step 4: Place the sample in a vacuum annealing furnace for ex-situ annealing at a temperature of 400°C for 1 h.

[0060] Figure 3 The in-plane and out-of-plane hysteresis loops of MgO / CoFeB / W annealed at 400℃ for 1h are shown. Figure 2 The difference is obvious, indicating that after inserting the Mo isolation layer, the perpendicular magnetic anisotropy of the sample is significantly enhanced, and the effective anisotropy constant (K eff ) from 1.41×10 6 erg / cm 3 Increased to 2.38×10 6 erg / cm 3 Table 1 Effective anisotropic constants (K) of MgO / CoFeB / Mo / W and MgO / CoFeB / W annealed at 400℃ for 1h eff ).

[0061] <![CDATA[Effective anisotropy constant (K eff )]]> Example 1 <![CDATA[2.38×10 6 erg / cm 3 ]]> Comparative Example 1 <![CDATA[1.41×10 6 erg / cm 3 ]]>

[0062] Example 2

[0063] The preparation method of this embodiment is basically the same as that of embodiment 1, except for the annealing temperature, which is shown in:

[0064] The annealing temperature in step 5 of Example 1 was changed to 450°C.

[0065] Figure 4 Shown are the in-plane and out-of-plane hysteresis loops of MgO / CoFeB / Mo / W annealed at 450°C for 1 h.

[0066] Comparative Example 2:

[0067] The preparation method of this comparative example is basically the same as that of comparative example 1, except for the annealing temperature, which is reflected in:

[0068] The annealing temperature in step 4 of Comparative Example 1 was changed to 450°C.

[0069] Figure 5 Shown are the in-plane and out-of-plane hysteresis loops of MgO / CoFeB / W annealed at 450℃ for 1h. Figure 4 The difference is obvious, indicating that after inserting the Mo isolation layer, the perpendicular magnetic anisotropy of the sample is significantly enhanced, and the effective anisotropy constant (K eff ) from 6.43×10 5 erg / cm 3 Increased to 1.28×10 6 erg / cm 3 Table 2 Effective anisotropic constants (K) of MgO / CoFeB / Mo / W and MgO / CoFeB / W annealed at 450℃ for 1h eff ).

[0070] <![CDATA[Effective anisotropy constant (K eff )]]> Example 2 <![CDATA[1.28×10 6 erg / cm 3 ]]> Comparative Example 2 <![CDATA[6.43×10 5 erg / cm 3 ]]>

[0071] Example 3

[0072] The preparation method of this embodiment is basically the same as that of embodiment 1, except for the annealing temperature, which is shown in:

[0073] The annealing temperature in step 5 of Example 1 was changed to 500°C.

[0074] Figure 6 Shown are the in-plane and out-of-plane hysteresis loops of MgO / CoFeB / Mo / W annealed at 500°C for 1 h.

[0075] Comparative Example 3:

[0076] The preparation method of this comparative example is basically the same as that of comparative example 1, except for the annealing temperature, which is reflected in:

[0077] The annealing temperature in step 4 of Comparative Example 1 was changed to 500°C.

[0078] Figure 7 The in-plane and out-of-plane hysteresis loops of MgO / CoFeB / W annealed at 500℃ for 1h are shown. Figure 6The difference is obvious, indicating that after inserting the Mo isolation layer, the perpendicular magnetic anisotropy of the sample is significantly enhanced, and the effective anisotropy constant (K eff ) from 5.99×10 5 erg / cm 3 Increased to 7.12×10 5 erg / cm 3 Table 3 Effective anisotropic constants (K) of MgO / CoFeB / Mo / W and MgO / CoFeB / W annealed at 500℃ for 1h eff ).

[0079] <![CDATA[Effective anisotropy constant (K eff )]]> Example 3 <![CDATA[7.12×10 5 erg / cm 3 ]]> Comparative Example 3 <![CDATA[5.99×10 5 erg / cm 3 ]]>

[0080] Example 4

[0081] The preparation method of this embodiment is basically the same as that of Example 1, except that:

[0082] Step 4 in Example 1 is modified as follows: depositing a 2 nm thick Hf layer on the Mo layer by DC magnetron sputtering.

[0083] Example 5

[0084] The preparation method of this embodiment is basically the same as that of Example 1, except that:

[0085] Step 4 in Example 1 was modified as follows: a Ta layer with a thickness of 3 nm was deposited on the Mo layer by DC magnetron sputtering.

Claims

1. A method for enhancing the perpendicular magnetic anisotropy of a CoFe-based magnetic multilayer film, characterized in that: The specific steps are as follows: Step 1. Preparation of MgO layer: Deposition directly on the substrate by radio frequency magnetron sputtering; Step 2. Preparation of CoFe-based magnetic layer: depositing a CoFe-based magnetic layer on the MgO layer by radio frequency magnetron sputtering; Step 3. Preparing a Mo isolation layer: depositing a Mo isolation layer on the CoFe-based magnetic layer by DC magnetron sputtering; Step 4. Preparing a heavy metal layer: depositing a heavy metal layer on the Mo isolation layer by DC magnetron sputtering; wherein the heavy metal layer is a W layer; Step 5. Annealing: After the heavy metal layer (5) is deposited, the sample is annealed; In step 1, the substrate is a Si substrate; The sputtering atmosphere is argon, and the argon flow rate is 18 sccm-36 sccm; The substrate rotation speed of the magnetron sputtering system is 5rpm-20rpm; In step 4, the material used for the deposited heavy metal layer is a material with a surface free energy higher than 2939 mJ / m 2 Non-ferromagnetic heavy metals; In step 5, the annealing temperature is 400°C-500°C, and the annealing time is 1 hour; The thickness of the MgO layer is 2 nm; the thickness of the CoFe-based magnetic layer is 1 nm to 1.7 nm; the thickness of the Mo isolation layer is 1 nm to 4 nm; and the thickness of the heavy metal layer is 2 nm to 4 nm.

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