Method for preparing (Fe1-xNix) 5GeTe2 crystal

Abstract

The invention discloses a method for preparing (Fe1-xNix) 5GeTe2 crystals. The method comprises the following steps: carrying out programmed heating / cooling sintering on Fe powder, Ni powder, Ge powder, Te powder and a transport agent under a vacuum condition; the programmed heating / cooling comprises the following steps: heating to 900-1050 DEG C, keeping the temperature for 1200-2000 minutes, and cooling to 730-750 DEG C; the balance of reversible reaction is adjusted by controlling the temperature gradient, driving force is provided for crystal nucleation growth, and advanced precipitation of a binary phase and other impure phases is inhibited, so that the quality and yield of the (Fe < 1-x > Nix) 5GeTe2 crystal are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystal materials, and specifically relates to a method for preparing (Fe 1-x Ni x )5GeTe2 crystal method. Background Art

[0002] (Fe 1-x Ni x )5GeTe2 crystal is a layered van der Waals material with ferromagnetism above room temperature. This crystal material can be prepared into quasi-two-dimensional thin film material through micromechanical exfoliation technology, and is used in spin electronic devices such as magnetic tunnel junctions, logic switches, magnetoelectric sensors and magnetic random access memory.

[0003] Low-dimensional magnetic systems such as quasi-two-dimensional (2D) van der Waals (vdW) magnets have long-range magnetic order, where vdW Fe x The GeTe2 (x = 3, 4, 5; FGT) family has tunable magnetic properties. In particular, when x = 5 (F5GT), a ferromagnetic ordering temperature (T) above room temperature can be observed. C ). Studies have shown that replacing part of the iron in F5GT with nickel (Ni) can produce T C =478(6) K. More importantly, in the phase diagram of Ni-F5GT, room-temperature ferromagnetism is prevalent in all Ni doping ranges.

[0004] Currently (Fe 1-x Ni x 5GeTe2 crystals are prepared using a molar ratio of Fe:Ni:Ga:Te = x:y:1:2, where the sum of x and y is 6. The preparation method involves sintering in a tube furnace using a set schedule. This often results in crystals with a high concentration of impurities and a relatively low yield. Summary of the Invention

[0005] In view of the above technical problems, the present invention provides a high-quality and high-yield preparation (Fe 1-x Ni x )5GeTe2 crystal method.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] On the one hand, the present invention provides a preparation method of (Fe 1-x Ni x )5GeTe2 crystal method, comprising the following steps:

[0008] Fe powder, Ni powder, Ge powder, Te powder and transport agent are subjected to programmed temperature rise / fall sintering under vacuum conditions;

[0009] The programmed temperature rise / fall includes:

[0010] Heat to 900-1050°C and keep warm for 1200-2000 minutes, then cool to 730-750°C.

[0011] As a preferred embodiment, the heating rate to 900-1050° C. is 15-17.5° C. / min.

[0012] As a preferred embodiment, the cooling to 730-750° C. includes:

[0013] Stage i: cooling to 850-900°C at a constant cooling rate of 1.5-2.5°C / min;

[0014] Stage ii: cooling at a constant rate of 0.016-0.017°C / min to 760-790°C;

[0015] Stage iii: cooling at a constant rate of 0.008-0.012°C / min to 730-750°C.

[0016] As a preferred embodiment, the transport agent is iodine particles.

[0017] As a preferred embodiment, the mass of the iodine particles is 1% to 2% of the total mass of the Fe powder, Ni powder, Ge powder and Te powder.

[0018] In the technical solution of the present invention, the theoretical molar ratio of the Fe powder, Ni powder, Ge powder and Te powder is x:y:1:2, wherein the sum of x and y is 5.

[0019] In certain specific embodiments, the Fe powder, Ni powder, Ge powder, Te powder, and transport agent are vacuum-sealed in a reaction vessel and subjected to programmed temperature increase in a muffle furnace. Preferably, in the reaction vessel, the Fe powder, Ni powder, Ge powder, Te powder, and transport agent are located near a muffle furnace thermocouple.

[0020] As a preferred embodiment, the vacuum degree is ≤2×10 -2 Pa.

[0021] Preferably, the Fe powder, Ni powder, Ge powder, Te powder, and transport agent are subjected to programmed temperature rise / fall sintering in an inclined reaction vessel; the tilt angle is ≤ 15°; the angle is horizontal. In the technical solution of the present invention, the tilt facilitates product nucleation and growth at the bottom of the reaction vessel, while a too large angle is not conducive to forming a large-area product.

[0022] As a preferred embodiment, the programmed temperature rise further includes a hot water quenching operation.

[0023] As a preferred embodiment, the temperature of the hot water is 80-100°C.

[0024] In certain specific embodiments, the purity of the Fe powder is 99.95%; the purity of the Ni powder is 99.99%; the purity of the Ge powder is 99.97%; the purity of the Te powder is 99.999%; and the purity of the iodine particles is 99.995%.

[0025] In another aspect, the present invention provides (Fe 1-x Ni x )5GeTe2 crystal.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention uses a programmed temperature method to prepare (Fe 1-x Ni x )5GeTe2 crystals, by controlling the temperature gradient and adjusting the balance of reversible reactions, provide a driving force for the crystal nucleation and growth while inhibiting the premature precipitation of binary phases and other impurity phases.

[0028] The present invention improves the ternary phase (Fe 1-x Ni x )5GeTe2 nucleation rate.

[0029] The present invention further improves the (Fe 1-x Ni x )5GeTe2 crystal purity and particle size, while eliminating the internal stress in crystal growth, avoiding the precipitation of Fe and improving the quality of the crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the placement of the quartz tube in an embodiment of the present invention;

[0031] Figure 2 A schematic diagram of the temperature program used for sintering in an embodiment of the present invention;

[0032] Figure 3 (Fe prepared in Example 1 of the present invention 1-x Ni x )Scanning electron micrograph (SEM) of 5GeTe2 crystal (x=0.05);

[0033] Figure 4 (Fe prepared in Example 1 of the present invention 1-x Ni x ) XRD pattern of 5GeTe2 crystal (x = 0 ~ 0.2);

[0034] Figure 5 (Fe prepared in Example 1 of the present invention 1-x Ni x )MT diagram of 5GeTe2 crystal (x=0.1);

[0035] Figure 6 Fe prepared in Example 1 of the present invention 1-x Ni x )MT diagram of 5GeTe2 crystal (x=0.05);

[0036] Figure 7 Fe prepared in Example 1 of the present invention 1-x Ni x MH diagram of 5GeTe2 crystal (x=0.05)

[0037] Figure 8 (Fe prepared in Example 2 of the present invention 1-x Ni x ) Physical image of 5GeTe2 crystal (x = 0.25 ~ 0.4);

[0038] Figure 9 (Fe prepared in Example 2 of the present invention 1-x Ni x ) XRD pattern of 5GeTe2 crystal (x = 0.25 ~ 0.4);

[0039] Figure 10 (Fe prepared in Example 2 of the present invention 1-x Ni x )5GeTe2 crystal (x=0.35) R xx -T figure.

[0040] Figure 11 The XRD pattern of the product prepared in the comparative example of the present invention is shown in FIG. DETAILED DESCRIPTION

[0041] The following embodiments are merely some of the embodiments of the present invention, rather than all of them. Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0042] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0043] The muffle furnace used in the embodiment of the present invention is a rapid heating high temperature muffle furnace manufactured by Tianjin Kaiheng Electric Heating Technology Co., Ltd.

[0044] Example 1:

[0045] In this embodiment, (Fe 1-x Ni x )5GeTe2 crystal, low-Ni doping, x = 0 to 0.2, prepared as follows:

[0046] Step 1: Raw material ratio: Reduced Fe powder (purity 99.95%), Ni powder (purity 99.99%), Ge powder (purity 99.999%), and Te powder (purity 99.999%) were weighed according to a molar ratio of (Fe+Ni):Ga:Te=5:1:2; the mass ratio of each raw material and the prepared material are shown in Table 1;

[0047] Table 1

[0048] x <![CDATA[(Fe 1-x In x )5GeTe2]]> Reduced Fe powder / g Ni powder / g Ge powder / g Te powder / g 0 <![CDATA[Fe5GeTe2]]> 0.837 0 0.2178 0.7656 0.05 <![CDATA[Fe 4.75 In 0.25 Get2]]> 0.7952 0.0442 0.2178 0.7656 0.1 <![CDATA[Fe 4.5 In 0.5 Get2]]> 0.7533 0.0881 0.2178 0.7656 0.15 <![CDATA[Fe 4.25 In 0.75 Get2]]> 0.7115 0.1321 0.2178 0.7656 0.2 <![CDATA[Fe4NiGeTe2]]> 0.6696 0.1761 0.2178 0.7656

[0049] Step 2: Vacuum sealing: The weighed reduced Fe powder, Ni powder, Ge powder, and Te powder were mixed evenly in a mortar and then fed into the bottom of a quartz tube with 20-35 mg of iodine particles through a thin aluminum foil. The inner diameter of the quartz tube was 9.8 mm. The quartz tube was vacuum sealed using an oxyhydrogen cutting machine under argon protection until the vacuum degree of the quartz tube was less than 2×10 -2 Pa, the final sealed quartz tube length is 150 mm;

[0050] Step 3: Adjust the position: Place the sealed quartz tube in the muffle furnace at an angle of less than 15°; the tip of the quartz tube is close to the furnace door, and the bottom containing the raw materials is close to the bottom of the furnace body thermocouple; Figure 1 As shown;

[0051] Step 4: Sintering: Set up the muffle furnace program:

[0052] Heat to 1000°C in 60 minutes and keep warm for 1440 minutes;

[0053] Cool down to 880℃ in 60min; cool down to 830℃ in 3000min; cool down to 780℃ in 3000min; cool down to 750℃ in 3000min;

[0054] Step 5: Quench with hot water at a temperature of 80-100°C.

[0055] Figure 2Schematic diagram of the temperature program used for sintering in Example 1. By controlling the temperature gradient and adjusting the balance of reversible reactions, a driving force is provided for crystal nucleation and growth while suppressing the premature precipitation of binary phases and other impurity phases, thereby obtaining high-quality single crystal samples.

[0056] Figure 3 (Fe prepared in Example 1 1-x Ni x )Scanning electron micrograph (SEM) of 5GeTe2 crystal (x=0.05). It can be seen from the figure that the sample shows obvious layered growth.

[0057] Figure 4 (Fe prepared in Example 1 1-x Ni x )5GeTe2 crystal (x = 0 ~ 0.2) at room temperature X-ray diffraction pattern (XRD), the diffraction peaks of each crystal material plane are consistent with the literature, no diffraction peaks of other crystal planes were observed.

[0058] Figure 5 、 6 (Fe 1-x Ni x )5GeTe2(x=0.1) and (Fe 1-x Ni x )5GeTe2(x=0.05) magnetization intensity (M) variation curve (MT) with temperature (T) under magnetic field (H) cooling, where the applied magnetic field is 1000Oe, the MT temperature range is from 10K to 360K, in plane means the magnetic field is parallel to the crystal ab plane, out of plane means the magnetic field is perpendicular to the crystal ab plane and parallel to the crystal c axis.

[0059] Figure 7 (Fe prepared in Example 1 1-x Ni x )5GeTe2 crystal (x = 0.05) at different temperatures (T = 2K ~ 350K) magnetization intensity (M) versus magnetic field (H) curve (MH), where the sweep range is ± 50kOe. In plane means the magnetic field is parallel to the crystal ab plane, and out of plane means the magnetic field is perpendicular to the crystal ab plane and parallel to the crystal c axis. It can be seen that the MH spectrum shows typical ferromagnetic behavior. (Fe 1-x Ni x )5GeTe2 crystal (x=0.05) has obvious magnetic anisotropy, and the c-axis is the difficult magnetization axis.

[0060] Example 2:

[0061] In this embodiment, (Fe 1-x Ni x )5GeTe2 crystal, Ni is highly doped, x = 0.25 to 0.4, the preparation method is as follows:

[0062] Step 1: Raw material ratio: Reduced Fe powder (purity 99.95%), Ni powder (purity 99.99%), Ge powder (purity 99.999%), and Te powder (purity 99.999%) were weighed according to the molar ratio of (Fe+Ni):Ga:Te=5:1:2; the mass ratio of each raw material and the prepared material are shown in Table 2;

[0063] Table 2

[0064] x <![CDATA[(Fe 1-x In x )5GeTe2]]> Reduced Fe powder / g Ni powder / g Ge powder / g Te powder / g 0.25 <![CDATA[Fe 3.75 In 1.25 Get2]]> 0.6277 0.2201 0.2178 0.7656 0.3 <![CDATA[Fe 3.5 In 1.5 Get2]]> 0.5859 0.2642 0.2178 0.7656 0.35 <![CDATA[Fe 3.25 In 1.75 Get2]]> 0.5441 0.3082 0.2178 0.7656 0.4 <![CDATA[Fe3Ni2GeTe2]]> 0.5022 0.3534 0.2178 0.7656

[0065] Step 2: Vacuum sealing: The weighed reduced Fe powder, Ni powder, Ge powder, and Te powder were mixed evenly in a mortar and then fed into the bottom of a quartz tube with 20-35 mg of iodine particles through a thin aluminum foil. The inner diameter of the quartz tube was 9.8 mm. The quartz tube was vacuum sealed using an oxyhydrogen cutting machine under argon protection until the vacuum degree of the quartz tube was less than 2×10 -2 Pa, the final sealed quartz tube length is 150 mm;

[0066] Step 3: Adjust the position: Place the sealed quartz tube in the muffle furnace at an angle of less than 15°; the tip of the quartz tube is close to the furnace door, and the bottom containing the raw materials is close to the bottom of the furnace body thermocouple; Figure 1 As shown;

[0067] Step 4: Sintering: Same as Example 1.

[0068] Step 5: Quenching with hot water at 80-100°C

[0069] Figure 8 (Fe prepared in Example 2 1-x Ni x )5GeTe2 crystal (x = 0.25-0.4). The sample appears as a molten, thin block with a metallic luster. Microscopic observation reveals layered stacking, a defect-free surface, and easy exfoliation. The large sample area and regular surface make it easy to meet the requirements of magnetic measurements, crystal characterization, and mechanical exfoliation.

[0070] Figure 9 (Fe prepared in Example 2 1-x Ni x )5GeTe2 crystal (x = 0.25 ~ 0.4) at room temperature X-ray diffraction pattern (XRD), the diffraction peaks of each crystal material plane are consistent with the literature, with the incorporation of Ni, the peak position shifts to the left, the extra peak position is the peak of other crystal planes.

[0071] Figure 10 (Fe prepared in Example 2 1-x Ni x )5GeTe2 crystal (x = 0.35) measured lateral resistance (R xx ) changes with temperature (T), R xx It is a characteristic of metals that their capacitance gradually decreases as the temperature decreases.

[0072] Comparative Example

[0073] This comparative example was prepared according to the method in the literature "Pervasive beyond room-temperature ferromagnetism inadoped van der Waals magnet" (Fe 1-x Ni x )5GeTe2 crystal, x = 0 to 0.3, specifically as follows:

[0074] This paper adopts CVT method to prepare (Fe 1-x Ni x )5GeTe2 crystal: Reduced Fe powder, Ni powder, Ge powder, Te powder and iodine particles are sequentially fed into the bottom of a quartz tube through a thin aluminum foil in proportion. After vacuum sealing, the tube is placed in a furnace with a temperature gradient of 750-700°C for one week, and then cooled to room temperature along with the furnace.

[0075] The XRD pattern of the product prepared in this comparative example is shown in FIG. Figure 11 As shown in the figure, it can be seen that the prepared product has many impurity peaks and poor crystallinity, so it is impossible to prepare (Fe 1-x Ni x )5GeTe2 crystal materials, especially those with high doping ratio (Fe 1-x Ni x )5GeTe2 crystal material.

[0076] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing (Fe 1-x Ni x )5GeTe2 crystal method, characterized in that, The following steps are involved: Fe powder, Ni powder, Ge powder, Te powder and transport agent are subjected to programmed temperature rise / fall sintering under vacuum conditions; The programmed temperature rise / fall includes: Heat to 900-1050°C and keep warm for 1200-2000 minutes, then cool to 730-750°C.

2. The method according to claim 1, characterized in that The heating rate to 900-1050°C is 15-17.5°C / min.

3. The method according to claim 1, characterized in that The cooling to 730-750° C. comprises: Stage i: cooling to 850-900°C at a constant cooling rate of 1.5-2.5°C / min; Stage ii: cooling at a constant rate of 0.016-0.017°C / min to 760-790°C; Stage iii: cooling at a constant rate of 0.008-0.012°C / min to 730-750°C.

4. The method according to claim 1, wherein The transport agent is iodine particles.

5. The method according to claim 4, characterized in that The mass of the iodine particles is 1% to 2% of the total mass of the Fe powder, Ni powder, Ge powder and Te powder.

6. The method according to claim 1, characterized in that The vacuum degree is ≤2×10 -2 Pa.

7. The method according to claim 1, characterized in that The Fe powder, Ni powder, Ge powder, Te powder and transport agent are subjected to programmed temperature increase / decrease sintering in a tilted reaction container; the tilt angle is ≤15°.

8. The method according to claim 1, characterized in that The programmed temperature rise also includes a hot water quenching operation.

9. The method according to claim 8, characterized in that The temperature of the hot water is 80-100°C.

10. The method according to any one of claims 1 to 9 prepared (Fe 1-x Ni x )5GeTe2 crystal.

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