CN111549317B - Cobalt-based Heusler alloy structure and preparation method for improving ordering of cobalt-based Heusler alloy structure - Google Patents

Abstract

A preparation method for improving the structural ordering of a cobalt-based Heusler alloy, comprising the following steps: cleaning a sample substrate; co-sputtering a low-vapor pressure element and a cobalt-based Heusler alloy to form a film; and high-vacuum annealing treatment. The invention proposes a method of annealing after doping with low vapor pressure elements to improve the properties of the cobalt-based Heusler alloy thin film material, so that it has the advantages of high crystallinity, low temperature ordering and high spin polarizability.

Description

Cobalt-based Heusler alloy structure and preparation method for improving its ordering

technical field

The invention relates to the technical field of electronic device preparation, in particular to a cobalt-based Heusler alloy structure and a preparation method for improving the ordering thereof.

Background technique

Spintronic devices such as Giant Magnetoresistance GMR (Giant Magnetoresistance) and Tunneling Magnetoresistance TMR (Tunneling Magnetoresistance) are now widely used in information technology fields such as computer hard disk heads, memory, and industrial control sensors. With the rapid development of big data and Internet of Things technologies, there is an increasing demand for fast, efficient, and low-power acquisition, storage, and computing of massive information data. To meet this demand, there is an urgent need to develop next-generation, higher-performance spintronic devices. Among them, the development of thin film materials with high spin polarizability properties like Heusler alloys is the key to the preparation of high-performance spintronic devices.

Heusler alloys are a class of intermetallic compounds, which were first discovered by F.Heulser in 1903. At that time he found that the elements in Cu ₂ MnAl are all non-ferromagnetic elements, but this compound is ferromagnetic. Heusler alloys with a highly ordered structure show very rich physical properties and contain a variety of application functions, such as semi-metallic properties, ferromagnetism, thermoelectric effect, magnetoresistance effect, superconductivity, shape memory effect, etc. Heusler alloys can be divided into two categories: half-Heusler and full-Heusler, which are a huge family of alloys, as shown in Figure 1. Among them, cobalt-based full-Heusler alloys are favored by researchers because of their high spin polarizability, high Curie temperature, low damping factor, and good lattice matching with GaAs, MgO and other substrates.

Since the semi-metallic properties of cobalt-based Heusler alloys (the so-called semi-metallic properties refer to the fact that there is only one electron with one spin direction near the Fermi surface of the energy band structure of the material, so theoretically it has 100% spin polarizability.) Since its discovery, people have been working hard to explore new cobalt-based Heusler alloy materials with 100% high spin polarizability at room temperature that can be practically used in spintronic devices.

At present, among the reported high spin polarizability cobalt-based Heusler alloy thin film materials, it is generally necessary to obtain an ordered L2 ₁ crystal structure through a high temperature annealing process (above 500 degrees Celsius), thereby improving the spin polarizability of the thin film material. However, the high temperature annealing process above 500 degrees Celsius is too high for the preparation of spintronic devices, which is incompatible with the current silicon-based device fabrication process, which seriously limits the high-spin polarizability cobalt-based Heusler alloy thin film materials in high-performance spintronics. Applications in the fabrication of spintronic devices. Therefore, it is urgent to develop a new preparation process to solve the problems caused by high temperature annealing.

SUMMARY OF THE INVENTION

In view of this, the main purpose of the present invention is to provide a preparation method for improving the structural ordering of cobalt-based Heusler alloys, so as to partially solve at least one of the above technical problems.

In order to achieve the above purpose, as an aspect of the present invention, there is provided a preparation method for improving the structural ordering of cobalt-based Heusler alloys, comprising the following steps:

Sample substrate cleaning;

Co-sputtering of low vapor pressure elements and cobalt-based Heusler alloys;

High vacuum annealing treatment.

Wherein, in the step of cleaning the sample substrate, the sample substrate is ultrasonically cleaned with acetone, alcohol, and deionized water in sequence for 3-10 minutes each, and after the ultrasonic cleaning is completed, the sample substrate is placed in the vacuum chamber of the magnetron sputtering apparatus for Thermal cleaning at 500-800 degrees Celsius.

Wherein, the low vapor pressure element is zinc, magnesium, mercury, sodium, potassium, silver, gold, copper or titanium.

Wherein, the co-sputtering film formation of the low-vapor pressure element and the cobalt-based Heusler alloy specifically includes the following steps: using a cobalt-based Heusler alloy target and a low-vapor pressure element elemental target, and using a confocal magnetron sputtering method, Cobalt-based Heusler alloy thin films doped with low vapor pressure elements were prepared on sample substrates.

Wherein, the performance of the thin film material and the doping concentration of the low vapor pressure element are determined by the sputtering time, sputtering temperature, sputtering power, power supply type, process gas pressure, flow rate, sputtering power, The mesh size of the barrier mesh and the target-sample distance parameters are controlled.

Wherein, in the step of high vacuum annealing treatment, the prepared thin film material is subjected to annealing treatment at 300-600 degrees Celsius in an ultra-high vacuum sputtering chamber with a vacuum degree of ^{10 -6} -10 ^-8 Pa, and the annealing time is 10-120 minutes.

Wherein, the preparation method can be extended and applied to all cobalt-iron-based (Co ₂ Fe-based) and cobalt-manganese-based (Co ₂ Mn-based) Heusler alloy material systems.

As another aspect of the present invention, a cobalt-based Heusler alloy structure prepared by the above-mentioned preparation method is provided.

Wherein, the cobalt-based Heusler alloy thin film material can be used for the preparation of spintronic devices, and for improving the performance of hard disk magnetic heads, magnetic random access memories, magnetic sensors or spin logic circuit products.

Based on the above technical solutions, it can be known that the preparation method for improving the structural ordering of cobalt-based Heusler alloys of the present invention has at least one of the following beneficial effects relative to the prior art:

1. The present invention proposes a method of annealing after doping with low vapor pressure elements to improve the properties of the cobalt-based Heusler alloy thin film material, so that it has the advantages of high crystallinity, low temperature ordering, and high spin polarizability.

2. The method of using low vapor pressure element doping and annealing to improve the performance of thin film materials proposed in the present invention can be extended to all Co ₂ Fe-based, Co ₂ Mn-based Heusler in the alloy material system.

3. The high-performance cobalt-based Heusler alloy thin film material prepared by the present invention can be used for the preparation of high-performance spintronic devices, and for improving the performance of hard disk heads, magnetic random access memories, magnetic sensors, spin logic circuits and other products.

Description of drawings

Figure 1 is the periodic table of the elements of Heusler alloy;

Fig. 2 is the preparation method flow chart of the embodiment of the present invention;

3 is a schematic diagram of co-sputtering film formation of low vapor pressure elements and cobalt-based Heusler alloys according to an embodiment of the present invention;

4 is a cross-sectional structural diagram of a thin film material sample prepared according to a preparation method according to an embodiment of the present invention;

Fig. 5 is a graph of the L2 ₁ lattice order of Co ₂ FeGa _0.5 Ge _0.5 films containing different zinc doping concentrations at different annealing temperatures;

FIG. 6 is a graph showing the change of the content of zinc element in Co ₂ FeGa _0.5 Ge _0.5 thin films prepared under different sputtering conditions at different annealing temperatures.

Detailed ways

In the present invention, the cobalt-based Heusler alloy (Heusler alloy) is doped with an element with low vapor pressure and subjected to high vacuum annealing to prepare a high-performance cobalt-based Heusler alloy thin film material, and the thin film material has high crystallinity. , low-temperature ordering, and high spin polarizability, which can provide a material basis for the preparation of high-performance spintronic devices.

In previous studies, high-temperature annealing (above 500 degrees Celsius) process was usually used to obtain cobalt-based Heusler alloy thin film materials with L2 ₁ crystal structure with high lattice order. In the patent of the present invention, the inventor found that after co-sputtering doping of cobalt-based Heusler alloy with low vapor pressure elements (zinc, magnesium, mercury, sodium, potassium, silver, gold, copper, titanium, etc.) High-performance cobalt-based Heusler alloy thin films can be prepared by annealing in a high vacuum environment. The thin films have the advantages of high crystallinity, low-temperature ordering, and high spin polarizability. Preparation provides the material basis. The specific preparation process is shown in Figure 2.

In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

1. Sample substrate cleaning

The sample substrate was ultrasonically cleaned with acetone, alcohol, and deionized water in sequence for 5 minutes each. After the end, put it into the vacuum chamber of the magnetron sputtering apparatus for thermal cleaning at 600 degrees Celsius.

2. Co-sputtering film formation of low vapor pressure elements and cobalt-based Heusler alloys

As shown in Figure 3, the preparation steps of co-sputtering film formation of low vapor pressure elements and cobalt-based Heusler alloys are as follows: using cobalt-based Heusler alloy targets and low-vapor pressure element elemental targets, using the method of confocal magnetron sputtering, Cobalt-based Heusler alloy thin films doped with low vapor pressure elements were prepared on sample substrates. Among them, the thickness of the film and the doping concentration of the low vapor pressure element are determined by the sputtering time, sputtering temperature, sputtering power, power supply type, process gas pressure, flow rate, sputtering power, barrier mesh in the magnetron sputtering process. Parameters such as hole size and target-sample distance can be adjusted.

3. High vacuum annealing treatment

The prepared thin film samples were annealed at 500 degrees Celsius in an ultra-high vacuum sputtering chamber with a vacuum degree of 10 ^-7 Pa, and the annealing time was 30 minutes.

As shown in FIG. 4 , it is a cross-sectional structure diagram of the high-performance cobalt-based Heusler alloy thin film material sample prepared by the above method.

In a further embodiment of the present invention, the performance of the Heusler thin film material Co ₂ FeGa _0.5 Ge _0.5 (CFGG for short) is improved by doping with zinc element.

As shown in Fig. 5, the crystallinity of the CFGG films became better and better with the increase of the zinc doping concentration, and the ordering annealing temperature of the L21 lattice of the _CFGG films decreased. For example, the ordering temperature of L2 ₁ lattice in the samples doped with 0%, 1.1% and 4.8% zinc element is 600 degrees Celsius, when 12.8% doping, the ordering temperature of L2 ₁ lattice drops to 500 degrees Celsius, 17.9 % and 43.9% doping, it further drops to 400 degrees Celsius.

As shown in Fig. 6, as the annealing temperature increases, the zinc element in the CFGG film gradually precipitates out of the sample. Under the annealing conditions of 600 degrees Celsius, 30 minutes, and 10 ^-7 Pa, the doped zinc element is almost completely precipitated before annealing. , escape the sample. The method of improving the crystallinity, lattice ordering and spin polarizability of Heusler alloy thin films by the precipitation and evaporation of zinc has not been reported before.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned specific embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principle of the present invention, any modifications, equivalent replacements, improvements, etc. made should be included within the protection scope of the present invention.

Claims (5)

1. A preparation method for improving the structural ordering of a cobalt-based Heusler alloy is characterized by comprising the following steps of:

cleaning a sample substrate;

co-sputtering low vapor pressure element and cobalt-based Heusler alloy to form a film, and preparing the low vapor pressure element doped cobalt on a sample substrate by using a cobalt-based Heusler alloy target and a low vapor pressure element simple substance target and utilizing a confocal magnetron sputtering methodThe base Heusler alloy thin film material is characterized in that the low steam pressure element is a zinc element, and the cobalt-based Heusler alloy thin film material is Co ₂ FeGa _0.5 Ge _0.5 ；

High vacuum annealing treatment, wherein in the high vacuum annealing treatment step, the prepared film material has the vacuum degree of 10 ^-7 And (3) annealing treatment at 600 ℃ in an ultrahigh vacuum sputtering chamber of Pa for 30 minutes.

2. The method as claimed in claim 1, wherein in the step of cleaning the sample substrate, the sample substrate is sequentially cleaned by ultrasonic cleaning with acetone, alcohol and deionized water for 3-10 minutes, and after the ultrasonic cleaning, the sample substrate is placed in a vacuum chamber of a magnetron sputtering apparatus for thermal cleaning at 500-800 ℃.

3. The method according to claim 1, wherein the properties of the thin film material and the doping concentration of the low vapor pressure element are controlled by parameters of sputtering time, sputtering temperature, sputtering power, power type, process gas pressure, flow rate, size of mesh of the barrier net, and target-sample distance in the magnetron sputtering process.

4. A cobalt-based Heusler alloy thin film material prepared according to the preparation method as set forth in any one of claims 1 to 3.

5. The cobalt-based Heusler alloy thin film material according to claim 4, wherein the cobalt-based Heusler alloy thin film material can be used for the preparation of a spintronic device for improving the performance of a hard disk magnetic head, a magnetic random access memory, a magnetic sensor or a spintronic circuit product.

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