CN116145008A - Mn with zero field cold exchange bias effect 2-x FeCoNi medium-entropy alloy material and preparation method thereof - Google Patents

Abstract

The invention discloses a medium entropy alloy material with zero field cold exchange bias effect and a preparation method thereof, wherein the chemical formula of the material is Mn _2‑x FeCoNi, x is more than or equal to 0.2 and less than or equal to 0.4, mn is obtained by repeatedly smelting _2‑x The FeCoNi alloy is then sealed in a vacuum quartz tube and put into a muffle furnace for annealing to obtain the alloy. Mn of the present invention _{2‑ x} The entropy alloy material in FeCoNi has zero field cold exchange bias effect, the size of ferromagnetic and antiferromagnetic exchange coupling can be controlled by the composition change of Mn (0.2-0.4) to obtain specific antiferromagnetic and ferromagnetic coupling proportion, thus obtaining obvious zero field cold exchange bias field without additional external magnetic field accompanied with cooling process, and the material is used in magnetic memory unit and spin valve deviceThe spintronics field such as the parts has potential application prospect.

Description

A Mn2-xFeCoNi medium entropy alloy material with zero field cold exchange bias effect and its its preparation method

technical field

The invention relates to a magnetic medium-entropy alloy material, in particular to a Mn _2-x FeCoNi medium-entropy alloy material with a zero-field cold exchange bias effect and a preparation method thereof.

Background technique

The discovery of the exchange bias effect is due to Meiklejohn and Bean. The two researchers prepared CoO-wrapped Co particles by electrodeposition in 1956. CoO is antiferromagnetic, and Co is ferromagnetic. They found that under the action of a stable external magnetic field, when the temperature is greater than the Neel temperature ( _TN ) of CoO but less than the Curie temperature ( _TC ) of Co particles, the hysteresis loop will appear horizontal as the temperature decreases offset phenomenon. In 1999, Nogues et al. summarized the horizontal shift of the hysteresis loop caused by the coupling between the antiferromagnetic and ferromagnetic double-layer structures, and named it the exchange bias effect. Therefore, generally speaking, the exchange bias effect refers to the field cold exchange bias effect, which has attracted extensive attention due to its application in magnetic recording technology.

In 2011, Wang et al. reported for the first time in Ni ₅₀ Mn ₃₇ In ₁₃ that under the condition of zero magnetic field cooling, an exchange bias effect of up to 1300Oe can be obtained, and this can be achieved without applying an external magnetic field during the cooling process. The phenomenon that results in a shift in the hysteresis loop is named the spontaneous exchange bias effect or the zero-field cold exchange bias effect. So far, zero-field cold exchange bias effects have been observed in Ni-Mn-based Hasler alloy systems, magnetic exchange bias thin film composite systems, perovskite systems, and spinel oxide systems.

Recently, high-entropy alloys (alloys composed of five or more elements) have attracted extensive attention due to their excellent fracture strength, tensile strength, corrosion resistance, wear resistance, electrochemical properties, and magnetic properties. In 2017, Schneeweiss et al. first discovered the exchange bias effect in the vertical direction in equiatomic ratio CrMnFeCoNi; in 2022, Ling et al. deposited a layer of CrMnFeCoNi film on the MgO substrate by laser-assisted molecular beam epitaxy, and obtained the spontaneous exchange bias effect. effect. This indicates that the zero-field cold exchange bias effect can be obtained in CrMnFeCoNi high-entropy alloys by adjusting the ratio of antiferromagnetic/ferromagnetic coupling. However, there are several problems in regulating the zero-field cold exchange bias effect in the CrMnFeCoNi high-entropy alloy: 1. The atomic arrangement of the high-entropy alloy is highly disordered. There are local impurity clusters in the film, which will lead to the inability to obtain its intrinsic physical properties during the test of magnetic properties and crystal structure; 2. The zero-field cold exchange bias effect produced by the thin film system is too small, and the practical application is limited ; 3. Materials are prepared by laser-assisted molecular beam epitaxy, which has low yield and high cost.

Contents of the invention

The object of the present invention is to provide a Mn _2-x FeCoNi medium entropy alloy with zero-field cold exchange bias effect and a preparation method thereof.

A kind of preparation method of Mn _2-x FeCoNi medium entropy alloy with zero field cold exchange bias effect, it is made up of following steps:

Step 1: Batching: Calculate the mass of each element of Mn, Fe, Co and Ni according to the stoichiometric ratio Mn _2-x FeCoNi (0.2≤x≤0.4), wherein for the Mn element that is easy to volatilize in the arc melting process Process according to excess 5wt%, then weigh;

Step 2: Vacuum arc melting: Put the weighed raw materials into the crystallizer of the water-cooled auxiliary vacuum arc melting furnace, use a mechanical pump to reduce the pressure in the furnace to 5*10 ^-3 Pa, and fill the furnace with 0.6 atm The high-purity argon gas is repeatedly smelted 4 times under the melting current of 90~110A, and the Mn _2-x FeCoNi medium entropy alloy ingot can be obtained.

Step 3: Vacuum sealed tube annealing: After cutting the Mn _2-x FeCoNi medium entropy alloy ingot obtained in step 2, put it into a quartz tube, vacuumize the quartz tube, and seal the vacuum quartz tube with the alloy ingot with an oxyacetylene welding torch. live. Put the vacuum quartz tube sealing the alloy ingot into the muffle furnace, anneal at 800°C for 1h, and then quickly quench in cold water to obtain the Mn _2-x FeCoNi medium entropy alloy.

Compared with the prior art, the present invention has the following advantages:

On the basis of high-entropy alloys, the zero-field cold exchange bias effect is obtained in medium-entropy alloys by adjusting the composition changes. This medium-entropy alloy also inherits the strength and toughness of high-entropy alloys, which also broadens its application range in magnetic recording technologies such as spin valves.

The ferromagnetic coupling is enhanced by reducing the Mn content alone to obtain the right ratio of antiferromagnetic/ferromagnetic coupling to obtain the zero-field cold exchange bias effect.

Mn _{2- x} FeCoNi medium entropy alloy material with zero-field cold exchange bias effect was obtained through arc melting + vacuum sealed tube annealing + cold water rapid quenching. The process is simple, the requirements for equipment are low, the cost of raw materials is low, and it is convenient for mass production .

Description of drawings

Fig. 1 is the XRD pattern (a) and its partial enlarged view (b) of Mn _2-x FeCoNi (x=0, 0.2 and 0.3) medium entropy alloys.

Fig. 2 is a field cooling exchange bias effect map and a zero field cold exchange bias effect map of the Mn _2-x FeCoNi (x=0) medium entropy alloy in Example 1 of the present invention under the maximum circulating magnetic field at a temperature of 2K and 5T.

Fig. 3 is the field cold exchange bias effect map and the zero field cold exchange bias effect map of the Mn _2-x FeCoNi (x=0.2) medium entropy alloy in Example 2 of the present invention under the maximum circulating magnetic field at 2K temperature and 5T.

Fig. 4 is the field cold exchange bias effect map and the zero field cold exchange bias effect map of the Mn _2-x FeCoNi (x=0.3) medium entropy alloy in Example 3 of the present invention under the maximum circulating magnetic field at 2K temperature and 5T.

Figure 5 is the dependence of the exchange bias field and coercive force on the composition change of Mn _2-x FeCoNi (x=0, 0.2, 0.3 and 0.4) medium entropy alloys in Examples 1-4 of the present invention after zero-field cooling picture.

Fig. 6 shows the exchange bias field and coercive force of the Mn _2-x FeCoNi (x=0, 0.2, 0.3 and 0.4) medium entropy alloys in Examples 1-4 of the present invention after cooling in a 1T external magnetic field and the changes in composition Dependency graph.

Implementation

Considering the problems existing in the above-mentioned high-entropy alloys, the present invention at first excludes the influence of Cr element, because Cr atom provides antiferromagnetic coupling, Mn atom can change between antiferromagnetic coupling and ferromagnetic coupling with atomic spacing variation, and Ni, Co, and Fe are ferromagnetic coupling. When the influence of Cr is excluded, the change of magnetic coupling in the alloy is affected by Mn alone, which is easy to control, and the uniformity of the quaternary medium-entropy alloy is also higher than that of the quinary high-entropy alloy. Even better, the effect of bulk materials is larger than that of thin film materials, which is more suitable for practical applications. Based on this, the present invention proposes to adjust the exchange coupling relationship between Mn-Mn in the Mn _2-x FeCoNi mesotropic alloy by changing the composition of Mn element alone, so as to obtain the zero-field cold exchange bias effect.

The basic principle of the invention is: Fe, Co and Ni provide ferromagnetic coupling in the alloy, while the coupling of Mn atoms is determined by the Mn-Mn atomic distance. When the Mn-Mn atomic distance is less than 2.83 Å, it shows antiferromagnetic coupling; when the Mn-Mn atomic distance is larger than 2.83 Å, it shows ferromagnetic coupling. As the proportion of Mn atoms decreases, the Mn-Mn spacing increases and the ferromagnetic coupling increases, while the proportions of Fe, Co and Ni also increase accordingly, which also enhances the ferromagnetic coupling, which makes the overall ferromagnetic coupling in the medium entropy alloy enhanced. The initial magnetization process also makes the alloy obtain disordered spin glass-like behavior at low temperature. When the ferromagnetic/spin glass coupling coexists, the specific antiferromagnetic/ferromagnetic coupling ratio enables the present invention to control the zero-field cold exchange bias effect. This exchange bias effect without external cooling has broad application prospects in new magnetic devices and magnetic recording technologies.

The Mn _2-x FeCoNi medium entropy alloy with zero-field cold exchange bias effect of the present invention has a crystal structure characterized by X-ray diffraction (XRD), and a magnetic performance test characterized by a magnetic property measurement system (MPMS).

Example 1: Preparation and Magnetic Properties Test of Mn _2-x FeCoNi (x=0) Medium Entropy Alloy

Step 1: Calculate the mass of each element Mn, Fe, Co and Ni required according to the stoichiometric ratio Mn _2-x FeCoNi (x=0), wherein the Mn element that is easy to volatilize in the arc melting process is based on an excess of 5wt% processed, then weighed.

Step 2: Put the weighed raw materials into the water-cooled assisted vacuum arc melting furnace crystallizer, use a mechanical pump to reduce the internal pressure of the cavity to 5*10 ^-3 Pa, and then fill the cavity with 0.6atm high Pure argon, repeated melting 4 times under the current of 90A, can get Mn ₂ FeCoNi medium entropy alloy ingot.

Step 3: After cutting the Mn ₂ FeCoNi medium entropy alloy ingot obtained in step 2, put it into a quartz tube, vacuumize the inside of the quartz tube, and seal the vacuum quartz tube containing the alloy ingot with an oxyacetylene torch. Put the vacuum quartz tube sealing the Mn ₂ FeCoNi medium entropy alloy ingot into the muffle furnace, anneal at a temperature of 800°C for 1 hour, and then quickly quench in cold water to obtain a Mn ₂ FeCoNi medium entropy alloy with good uniformity.

The obtained Mn ₂ FeCoNi medium entropy alloy was characterized by XRD microstructure and MPMS magnetic properties. Figure 1 shows the XRD spectrum of the alloy, and Figure 2 shows the zero-field cooling and 1T external magnetic field cooling. The hysteresis loop under the maximum circulating magnetic field at a temperature of 2K and 5T, and the corresponding exchange bias field and coercive force values are shown in Figure 5 and Figure 6.

Example 2: Preparation and Magnetic Properties Test of Mn _2-x FeCoNi (x=0.2) Medium Entropy Alloy

Change "x=0" in the batching link in the preparation process of Example 1 to "x= _0.2 ". The XRD spectrum of the alloy is shown in Figure 1. Figure 3 shows the hysteresis loop at 2K temperature and 5T maximum circulating magnetic field after zero-field cooling and 1T external magnetic field cooling. The corresponding exchange The values of bias field and coercive force are shown in Fig. 5 and Fig. 6.

Example 3: Preparation and Magnetic Properties Test of Mn _2-x FeCoNi (x=0.3) Medium Entropy Alloy

Change the "x=0" of the batching link in the preparation process of Example 1 to "x= _0.3 ". The XRD spectrum of the alloy is shown in Figure 1. Figure 4 shows the hysteresis loop at 2K temperature and 5T maximum circulating magnetic field after zero-field cooling and 1T external magnetic field cooling, and the corresponding exchange The values of bias field and coercive force are shown in Fig. 5 and Fig. 6.

Example 4: Preparation and Magnetic Properties Test of Mn _2-x FeCoNi (x=0.4) Medium Entropy Alloy

The "x=0" in the batching link in the preparation process of Example 1 was changed to "x=0.4", and the other conditions of the preparation were the same as in Example 1, and the MPMS magnetic property characterization was performed on the obtained Mn _1.7 FeCoNi medium entropy alloy, corresponding Figure 5 and Figure 6 show the exchange bias field and coercive force values.

The test results show that the zero-field cold exchange bias effect can be obtained in the Mn _2-x FeCoNi (x=0, 0.2, 0.3 and 0.4) mestropic alloys after zero-field cooling. As shown in Figure 5 and Figure 6, as the Mn content decreases, the zero-field cold exchange bias field first decreases and then increases, and the peak effect is achieved at x=0.3. When the Mn content is further reduced, the zero-field cold exchange bias field Weakening, the field cooling exchange bias effect and the corresponding coercivity all show the same trend. As shown in the XRD pattern of Figure 1, this is because the original split peak of x=0 disappears during the process from x=0 to x=0.2, which indicates that a structural change has occurred, resulting in weakened ferromagnetic coupling, thus x =0.2, the zero-field cold-exchange bias effect nearly disappears, and the corresponding zero-field cold-exchange bias field decreases from 0.053kOe when x=0 to 0.0075kOe when x=0.2. When x=0.3, the maximum zero-field cold exchange bias field H _ZEB is 0.415kOe, and the corresponding coercive force is 3.385kOe. After 1T field cooling, under the maximum circulating magnetic field at 2K temperature and 5T, The obtained field cold exchange bias effect H _CEB is 3.79kOe, and the corresponding coercive force is 1.75kOe. When x=0.4, due to the change of ferromagnetic coupling and antiferromagnetic coupling ratio, the zero-field cold exchange bias field also decreases. At this time, the H _ZEB is 0.13kOe, and the corresponding coercive force is 0.76kOe.

Claims (6)

1. A medium entropy alloy material with zero field cold exchange bias effect, characterized in that: the chemical formula of the medium entropy alloy material with zero field cold exchange bias effect is Mn _2-x FeCoNi ，0.2≤x≤0.4。

2. The method as claimed in claim 1The medium entropy alloy material is characterized in that: when x=0.3, under 2K conditions, the medium entropy alloy material attains a maximum zero field cold exchange bias field (H) when the maximum circulating magnetic field reaches 5T _ZEB ) At 0.415kOe, the corresponding coercivity (H _C ) 3.385kOe.

3. A preparation method of a medium entropy alloy material with zero field cold exchange bias effect is characterized by comprising the following steps: the method comprises the following steps:

step 1, batching: according to stoichiometric ratio Mn _2-x FeCoNi, wherein x is more than or equal to 0.2 and less than or equal to 0.4, and the mass of each element of Mn, fe, co and Ni is calculated, wherein the element of Mn which is easy to volatilize is excessively weighed;

step 2, vacuum arc melting: weighing raw materials, and carrying out vacuum arc melting to obtain Mn _2-x Entropy alloy ingot in FeCoNi;

step 3, vacuum tube sealing annealing: mn as described above _2-x Cutting the FeCoNi intermediate entropy alloy ingot, then carrying out vacuum annealing at a certain temperature, and carrying out cold water rapid quenching to obtain the intermediate entropy alloy material.

4. A method as claimed in claim 3, wherein: the volatile Mn element is weighed out in 5% by weight excess.

5. A method as claimed in claim 3, wherein: the weighed raw materials are put into a water-cooling auxiliary vacuum arc melting furnace crystallizer, and the pressure in the furnace is reduced to 5 x 10 ^-3 Pa, charging 0.6atm high-purity argon into the furnace body, and repeatedly smelting for 4 times under the smelting current of 90-110A to obtain Mn _2-x Entropy alloy ingot in FeCoNi.

6. A method as claimed in claim 3, wherein: vacuum annealing was performed at 800℃for 1h.

Images