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

Abstract

The invention discloses a medium entropy alloy material with zero-field cold exchange bias effect and a preparation method thereof. The chemical formula of the material is Mn 2‑x FeCoNi, 0.2≤x≤0.4, firstly obtain Mn by repeated smelting 2‑x The FeCoNi alloy is then sealed in a vacuum quartz tube and placed in a muffle furnace for annealing. 2‑ x The FeCoNi medium-entropy alloy material has a zero-field cold exchange bias effect. The size of its ferromagnetic and antiferromagnetic exchange coupling can be controlled by changing the Mn composition (0.2≤x≤0.4) to obtain a specific antiferromagnetic and ferromagnetic coupling ratio, thereby obtaining an obvious zero-field cold exchange bias field without the need for an additional external magnetic field accompanying the cooling process. This material has potential application prospects in spin electronics fields such as magnetic storage units and spin valve devices.

Description

Technical Field

[0001] The present invention relates to a magnetic medium entropy alloy material, in particular to a Mn alloy material having a zero-field cold exchange bias effect. 2-x FeCoNi medium-entropy alloy material and preparation method thereof. Background Art

[0002] The discovery of the exchange bias effect should be attributed to Meiklejohn and Bean. In 1956, the two researchers prepared CoO-coated Co particles by electrodeposition. CoO is antiferromagnetic and Co is ferromagnetic. They found that under a stable external magnetic field, when the temperature is greater than the Neel temperature (T) of CoO, the exchange bias effect will be reversed. N ) is lower than the Curie temperature of Co particles (T C ), as the temperature decreases, the hysteresis loop will shift horizontally. 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, in general, the exchange bias effect refers to the field-cooled exchange bias effect, which has attracted widespread attention due to its application in magnetic recording technology.

[0003] In 2011, Wang et al. 50 Mn 37 In 13 It was first reported that an exchange bias effect of up to 1300Oe can be obtained under zero magnetic field cooling conditions, and this phenomenon of hysteresis loop shift without applying an external magnetic field during the cooling process was named spontaneous exchange bias effect or zero-field cold exchange bias effect. So far, people have observed the zero-field cold exchange bias effect in Ni-Mn-based Heusler alloy system, magnetic exchange bias film composite system, perovskite system and spinel oxide system.

[0004] Recently, high entropy alloys (alloys composed of five or more elements) have attracted widespread 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 vertical exchange bias effect in equiatomic CrMnFeCoNi; in 2022, Ling et al. deposited a layer of CrMnFeCoNi film on a MgO substrate by laser-assisted molecular beam epitaxy and obtained a spontaneous exchange bias effect. This shows that by regulating the ratio of antiferromagnetic / ferromagnetic coupling, a zero-field cold exchange bias effect can be obtained in CrMnFeCoNi high entropy alloys. However, there are several problems in regulating the zero-field cold exchange bias effect in CrMnFeCoNi high-entropy alloys: 1. The atomic arrangement of high-entropy alloys is highly chaotic, and even after heat treatment, the uniformity is poor. It is inevitable that local impurity clusters will exist in the alloy, which will result in the inability to obtain its intrinsic physical properties during magnetic or crystal structure testing; 2. The zero-field cold exchange bias effect generated by the thin film system is too small, and its practical application is limited; 3. The material is prepared by laser-assisted molecular beam epitaxy technology, but the yield is low and the cost is high. Summary of the invention

[0005] The purpose of the present invention is to provide a Mn with zero field cold exchange bias effect. 2-x FeCoNi medium-entropy alloy and preparation method thereof.

[0006] A Mn with zero-field cold exchange bias effect 2-x The preparation method of the FeCoNi medium entropy alloy comprises the following steps:

[0007] Step 1: Ingredients: According to the stoichiometric ratio of Mn 2-x FeCoNi (0.2≤x≤0.4) calculates the required mass of each element of Mn, Fe, Co and Ni, wherein the Mn element which is easily volatilized during the arc melting process is treated with an excess of 5wt% and then weighed;

[0008] Step 2: Vacuum arc melting: Place the weighed raw materials into the crystallizer of a water-cooled vacuum arc melting furnace, and use a mechanical pump to reduce the pressure in the furnace to 5*10 -3 Pa, fill the furnace with 0.6atm of high-purity argon gas, and smelt repeatedly for 4 times at a smelting current of 90~110A to obtain Mn 2-x FeCoNi medium entropy alloy ingot.

[0009] Step 3: Vacuum sealing annealing: The Mn obtained in step 2 2-xAfter the FeCoNi medium entropy alloy ingot is cut, it is placed in a quartz tube, the quartz tube is evacuated, and the vacuum quartz tube containing the alloy ingot is sealed with an oxyacetylene torch. The vacuum quartz tube containing the alloy ingot is placed in a muffle furnace, annealed at 800°C for 1h, and then rapidly quenched with cold water to obtain Mn 2-x FeCoNi medium entropy alloy.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] By adjusting the composition of high-entropy alloys, the zero-field cold exchange bias effect was obtained in medium-entropy alloys. 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.

[0012] The ferromagnetic coupling is enhanced by reducing the Mn content alone to obtain a proper antiferromagnetic / ferromagnetic coupling ratio, thereby achieving a zero-field cold exchange bias effect.

[0013] Through arc melting + vacuum tube annealing + cold water rapid quenching, Mn with zero-field cold exchange bias effect was obtained. 2- x FeCoNi medium-entropy alloy material has a simple process flow, low equipment requirements, low raw material cost, and is easy to mass produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Mn 2-x XRD spectra of FeCoNi (x=0, 0.2 and 0.3) medium-entropy alloys (a) and their local enlarged images (b).

[0015] Figure 2 is Mn in Example 1 of the present invention 2-x Field-cooled exchange bias effect diagram and zero-field-cooled exchange bias effect diagram of FeCoNi (x=0) medium entropy alloy under maximum cyclic magnetic field of 5T at 2K temperature.

[0016] Figure 3 Mn in Example 2 of the present invention 2-x Field-cooled exchange bias effect diagram and zero-field-cooled exchange bias effect diagram of FeCoNi (x=0.2) medium entropy alloy under maximum cyclic magnetic field of 5T at 2K temperature.

[0017] Figure 4 is Mn in Example 3 of the present invention 2-x Field-cooled exchange bias effect diagram and zero-field-cooled exchange bias effect diagram of FeCoNi (x=0.3) medium entropy alloy under maximum cyclic magnetic field of 5T at 2K temperature.

[0018] Figure 5 Mn in Examples 1-4 of the present invention2-x Dependence of the exchange bias field and coercivity on the composition of FeCoNi (x=0, 0.2, 0.3 and 0.4) medium entropy alloys after zero-field cooling.

[0019] Figure 6 Mn in Examples 1-4 of the present invention 2-x Composition dependence of the exchange bias field and coercivity of FeCoNi (x=0, 0.2, 0.3 and 0.4) medium entropy alloys after cooling in a 1 T external magnetic field. Implementation

[0020] Considering the problems existing in the above-mentioned high entropy alloys, the present invention first eliminates the influence of the Cr element. Since Cr atoms provide antiferromagnetic coupling, Mn atoms will change between antiferromagnetic coupling and ferromagnetic coupling as the atomic distance changes, while Ni, Co and Fe are ferromagnetic coupling. After eliminating the influence of the Cr element, the change of magnetic coupling in the alloy is affected by Mn alone, which is easy to control. The uniformity of the quaternary medium entropy alloy is better than that of the quinary high entropy alloy, and the effect of the bulk material is greater than that of the thin film material, which is more suitable for practical applications. Based on this, the present invention proposes to add Mn to the Mn element. 2-x In the FeCoNi medium-entropy alloy, the composition of the Mn element is changed alone to regulate the exchange coupling relationship between Mn and Mn, thereby obtaining the zero-field cold exchange bias effect.

[0021] The basic principle of the present invention is that 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 2.83Å, it exhibits antiferromagnetic coupling; when the Mn-Mn atomic distance is greater than 2.83Å, it exhibits ferromagnetic coupling. As the proportion of Mn atoms decreases, the Mn-Mn distance increases, the ferromagnetic coupling is enhanced, and the proportion of Fe, Co and Ni also increases accordingly, which also enhances the ferromagnetic coupling, which enhances the ferromagnetic coupling as a whole in the medium entropy alloy. The initial magnetization process also allows the alloy to obtain disordered spin glass-like behavior at low temperatures. When ferromagnetic / spin glass coupling coexists, the specific antiferromagnetic / ferromagnetic coupling ratio enables the present invention to regulate the zero-field cold exchange bias effect. This exchange bias effect that does not require additional external field cooling has broad application prospects in new magnetic devices and magnetic recording technology.

[0022] The invention provides a Mn with zero-field cold exchange bias effect 2-x FeCoNi medium entropy alloy, its crystal structure is characterized by X-ray diffraction (XRD), and its magnetic properties are characterized by magnetic property measurement system (MPMS).

[0023] Example 1: Mn 2-x Preparation and Magnetic Properties of FeCoNi (x=0) Medium Entropy Alloy

[0024] Step 1: According to the stoichiometric ratio of Mn 2-x FeCoNi (x=0) calculates the required masses of each element Mn, Fe, Co and Ni, among which the Mn element that is easily volatilized during the arc melting process is treated with an excess of 5wt% and then weighed.

[0025] Step 2: Place the weighed raw materials into the water-cooled vacuum arc melting furnace crystallizer and use a mechanical pump to reduce the pressure inside the cavity to 5*10 -3 Pa, then fill the cavity with 0.6atm of high-purity argon gas, and smelt it 4 times at a current of 90A to obtain Mn 2 FeCoNi medium entropy alloy ingot.

[0026] Step 3: The Mn obtained in step 2 2 After the FeCoNi medium entropy alloy ingot is cut, it is placed in a quartz tube, the quartz tube is evacuated, and the vacuum quartz tube containing the alloy ingot is sealed with an oxyacetylene torch. 2 The FeCoNi medium entropy alloy ingot is placed in a vacuum quartz tube in a muffle furnace, annealed at 800°C for 1 hour, and then rapidly quenched in cold water to obtain Mn with good uniformity. 2 FeCoNi medium entropy alloy.

[0027] The obtained Mn 2 FeCoNi medium entropy alloy was characterized by XRD microstructure and MPMS magnetic properties. Figure 1 The XRD spectrum of the alloy is given in Figure 2 The hysteresis loops at 2K and 5T maximum cyclic magnetic field after zero field cooling and 1T external magnetic field cooling are shown in the figure. The corresponding exchange bias field and coercive force values ​​are shown in the figure. Figure 5 , Figure 6 shown.

[0028] Example 2: Mn 2-x Preparation and Magnetic Properties of FeCoNi (x=0.2) Medium Entropy Alloy

[0029] The "x=0" in the batching process of Example 1 was changed to "x=0.2", and the other preparation conditions were the same as those of Example 1. 1.8 FeCoNi medium entropy alloys were characterized by XRD microstructure and MPMS magnetic properties. Figure 1 The XRD spectrum of the alloy is given in Figure 3 The hysteresis loops at 2K and 5T maximum cyclic magnetic field after zero field cooling and 1T external magnetic field cooling are shown in the figure. The corresponding exchange bias field and coercive force values ​​are shown in the figure. Figure 5 , Figure 6shown.

[0030] Example 3: Mn 2-x Preparation and Magnetic Properties of FeCoNi (x=0.3) Medium Entropy Alloy

[0031] The "x=0" in the batching process of Example 1 was changed to "x=0.3", and the other preparation conditions were the same as those of Example 1. 1.7 FeCoNi medium entropy alloys were characterized by XRD microstructure and MPMS magnetic properties. Figure 1 The XRD spectrum of the alloy is given in Figure 4 The hysteresis loops at 2K and 5T maximum cyclic magnetic field after zero field cooling and 1T external magnetic field cooling are shown in the figure. The corresponding exchange bias field and coercive force values ​​are shown in the figure. Figure 5 , Figure 6 shown.

[0032] Example 4: Mn 2-x Preparation and Magnetic Properties of FeCoNi (x=0.4) Medium Entropy Alloy

[0033] The "x=0" in the batching process of Example 1 was changed to "x=0.4", and the other preparation conditions were the same as those of Example 1. 1.7 The magnetic properties of FeCoNi medium entropy alloys were characterized by MPMS. The corresponding exchange bias field and coercive force values ​​are shown in Figure 5 , Figure 6 shown.

[0034] The test results show that after zero field cooling, it is possible to 2-x The zero-field cold exchange bias effect is obtained in FeCoNi (x=0, 0.2, 0.3 and 0.4) medium entropy alloys. Figure 5 , Figure 6 As shown in the figure, with the decrease of Mn content, the zero-field cold exchange bias field first decreases and then increases, and the effect peak is obtained at x=0.3. When the Mn content is further reduced, the zero-field cold exchange bias effect weakens, and the field cold exchange bias effect and the corresponding coercive force show the same trend. Figure 1 As shown in the XRD spectrum, this is because the original split peak at x=0 disappears during the process from x=0 to x=0.2, which indicates that a structural change has occurred, resulting in a weakening of the ferromagnetic coupling, so that the zero-field cold exchange bias effect is close to disappearing at x=0.2, and the corresponding zero-field cold exchange bias field decreases from 0.053kOe at x=0 to 0.0075kOe at x=0.2. When x=0.3, the maximum zero-field cold exchange bias field H is obtained. ZEBThe corresponding coercive force is 0.415 kOe, and the corresponding coercive force is 3.385 kOe. After 1 T field cooling, the field-cooled exchange bias effect H is obtained at 2 K temperature and 5 T maximum cyclic magnetic field. CEB is 3.79kOe, and the corresponding coercive force is 1.75kOe. When x=0.4, due to the change in the ratio of ferromagnetic coupling and antiferromagnetic coupling, the zero-field cold exchange bias field also decreases. ZEB It is 0.13kOe, and the corresponding coercive force is 0.76kOe.

Claims

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 medium-entropy alloy material according to claim 1, characterized in that: When x=0.3, at a temperature of 2K, when the maximum cyclic magnetic field reaches 5T, the medium entropy alloy material obtains the maximum zero-field cold exchange bias field H ZEB is 0.415kOe, and the corresponding coercive force H C It is 3.385kOe.

3. A method for preparing a medium-entropy alloy material with a zero-field cold exchange bias effect, characterized in that: The following steps are involved: Step 1, ingredients: according to the stoichiometric ratio of Mn 2-x FeCoNi, 0.2≤x≤0.4 Calculate the required mass of each element of Mn, Fe, Co and Ni, among which the volatile Mn element is weighed in excess of 5wt%; Step 2, vacuum arc melting: The weighed raw materials are melted by vacuum arc to obtain Mn 2-x FeCoNi medium entropy alloy ingot; Step 3, vacuum sealing annealing: the above Mn 2-x After the FeCoNi medium-entropy alloy ingot is cut, it is vacuum annealed at a temperature of 800° C. for 1 h, and then rapidly quenched in cold water to obtain the medium-entropy alloy material.

4. The method according to claim 3, characterized in that: Put the weighed raw materials into the crystallizer of the water-cooled vacuum arc melting furnace and reduce the pressure in the furnace to 5*10 -3 Pa, 0.6atm of high-purity argon gas was filled into the furnace, and the smelting was repeated 4 times at a smelting current of 90~110A to obtain Mn 2-x FeCoNi medium entropy alloy ingot.

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