A method for preparing multiferroic heterojunction BaTiO3-CoFe2O4 without substrate support

Abstract

The present invention belongs to the technical field of the preparation of multiferroic heterojunctions, and discloses a method for preparing a multiferroic heterojunction BaTiO3-CoFe2O4 without substrate support. BaTiO3 and CoFe2O4 are fully mixed according to a molar ratio of 1:(0.1-1), added to water, stirred to obtain a suspension, and then dried to obtain a powder; the powder is sintered at 500-700 °C for 1-2 h and cooled with the furnace; the sintered powder is added to 40-60 v% ethanol, stirred to obtain a suspension, and then the suspension is transferred to a supercritical device, carbon dioxide is injected into the supercritical device to make it reach the supercritical state, and the stirring reaction time is 3-5 h; then, it is cooled to room temperature in air and the carbon dioxide is slowly released to relieve the pressure, the supercritically treated suspension is separated, the supernatant is taken, dried, and the multiferroic heterojunction BaTiO3-CoFe2O4 is obtained. The present invention successfully prepares the multiferroic heterojunction BaTiO3-CoFe2O4 without substrate support, and this technology perfectly solves the problem of the substrate clamping effect of the multiferroic heterojunction; it solves the problem that it is difficult to control the thickness of the heterojunction, and the thickness can be controlled by adjusting the content of CoFe2O4.

Description

Technical Field

[0001] The invention belongs to the technical field of multiferroic heterojunction preparation, and in particular relates to a method for preparing a multiferroic heterojunction BaTiO3-CoFe2O4 without substrate support. Background Art

[0002] With the emergence of next-generation storage devices, higher requirements are placed on the reliability, energy efficiency and data transmission speed of materials. Ferromagnetic materials are used to write data in magnetic random access memory (MRAM) by adjusting the magnetization state of the material. However, this technology has high energy consumption, low write speed and overheating problems. Ferroelectric random access memory (FeRAM) devices increase the write speed by changing the polarization state of the material. However, slow read speed and destructive read operations are challenges faced by this technology. In this case, multiferroic materials with ferroelectric and ferromagnetic sequences have the potential to help achieve hybrid read and write operations. Due to physical limitations, single-phase multiferroic materials are extremely rare and also have the problem of low magnetoelectric coupling. Compared with single-phase multiferroic, composite materials provide strong magnetoelectric coupling at ambient temperature. However, there have always been two difficulties in the preparation technology of composite materials: 1. It is difficult to meet the requirements of chip devices in thickness; 2. The substrate clamping effect caused by the substrate during the preparation process. Summary of the invention

[0003] In view of the defects and shortcomings of the above-mentioned prior art, the object of the present invention is to provide a method for preparing a multiferroic heterojunction BaTiO3-CoFe2O4 without substrate support.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing a multiferroic heterojunction BaTiO3-CoFe2O4 without substrate support, the steps are as follows:

[0006] (1) BaTiO3 and CoFe2O4 are fully mixed in a molar ratio of 1: (0.1-1), added to water, stirred to obtain a suspension, and then dried to obtain a powder; the powder is sintered at 500-700 ° C for 1-2 h, and cooled in the furnace;

[0007] (2) Add the sintered powder into 40-60 v% ethanol and stir to obtain a suspension. Then transfer the suspension to a supercritical device and inject carbon dioxide into the supercritical device to make it reach a supercritical state. The stirring reaction time is 3-5 hours. After that, cool to room temperature in the air and slowly release the carbon dioxide to relieve the pressure. Separate the suspension after supercritical treatment, take the supernatant, and dry it to obtain a multiferroic heterojunction BaTiO3-CoFe2O4.

[0008] Preferably, in step (1), the temperature is raised to the sintering temperature at a rate of 5-10 °C / min.

[0009] Preferably, in step (1), for every 0.01 mol of BaTiO3, the amount of water used is 40-60 ml.

[0010] Preferably, in step (2), the mass-volume ratio of the sintered powder to ethanol is 60 mg∶(40-60) ml.

[0011] Preferably, in step (2), the supercritical temperature is 80-120 °C and the pressure is 10-16 MPa.

[0012] Preferably, in step (2), the separation method is centrifugal separation.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] (1) The present invention uses supercritical fluid exfoliation technology to prepare a multiferroic heterojunction with both ferromagnetic and ferroelectric properties, and successfully embeds CoFe2O4 into the BaTiO3 matrix without substrate support, which perfectly solves the problem of substrate clamping effect in multiferroic heterojunctions;

[0015] (2) The present invention effectively realizes the exfoliation of bulk materials and the self-assembly of two-phase materials, and has good prospects in the application of future storage devices;

[0016] (3) The present invention solves the problem of difficult control of the heterojunction thickness, and completely realizes thickness control by adjusting the content of CoFe2O4; this preparation technology has the technical advantages of strong adaptability, controllability, and easy operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : Digital photo of the multiferroic heterojunction BaTiO3-CoFe2O4 prepared in Example 1 of the present invention.

[0018] Figure 2 : Transmission electron microscope characterization of the multiferroic heterojunction BaTiO3-CoFe2O4 prepared in Example 1 of the present invention.

[0019] Figure 3 : Hysteresis loop (VSM) of the multiferroic heterojunction BaTiO3-CoFe2O4 prepared in Example 1 of the present invention.

[0020] Figure 4 : Electric hysteresis loop (PE) of the multiferroic heterojunction BaTiO3-CoFe2O4 prepared in Example 1 of the present invention.

[0021] Figure 5:Atomic force microscopy images of the multiferroic heterojunction BaTiO3-CoFe2O4 prepared in Examples 1-4. Detailed implementation manners

[0022] To make the present invention clearer and more definite, the following further details the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] Example 1

[0024] 0.01 mol of BaTiO3 and 0.01 mol of CoFe2O4, i.e., a molar ratio of 1:1, were fully mixed and added to 50 ml of water, stirred to obtain a suspension, and then dried to obtain a powder. The powder was then transferred to a tubular furnace and heated to 700 °C at a rate of 5 °C / min and held for 1 h, and then cooled with the furnace; 60 mg of the sintered powder was added to 50 ml of 50 v% ethanol and stirred to disperse to obtain a suspension. Then the suspension was transferred to a supercritical reaction kettle, and carbon dioxide was injected into the reaction kettle to reach the supercritical state, with a temperature of 120 °C and a pressure of 14 MPa, and magnetically stirred for 4 h. After that, it was cooled to room temperature in air and then slowly released of carbon dioxide to relieve pressure. The supernatant was obtained by centrifugal separation of the supercritically treated suspension, and the obtained supernatant was dried in an oven at 65 °C to obtain the multiferroic heterojunction BaTiO3-CoFe2O4, labeled as BTO-1CFO.

[0025] The structure of the multiferroic heterojunction BaTiO3-CoFe2O4 was characterized by transmission electron microscopy (TEM), and the hysteresis loop (VSM) test was carried out using a physical property measurement system (PPMS-9), and the polarization-electric field hysteresis loop (PE) test was carried out using a ferroelectric analyzer (ACIX TF2000E, Germany).

[0026] The digital photo of the prepared multiferroic heterojunction BaTiO3-CoFe2O4 is shown in Figure 1 , and the sample presents as a grayish-black powder.

[0027] The transmission electron microscopy image of the prepared multiferroic heterojunction BaTiO3-CoFe2O4 is shown in Figure 2 , and it can be seen that: an obvious interface between the two phases, proving the formation of the heterojunction, where CFO represents CoFe2O4 and BTO represents BaTiO3.

[0028] The hysteresis loop (VSM) of the prepared multiferroic heterojunction BaTiO3-CoFe2O4 is shown in Figure 3 , and it can be seen that: the saturation magnetization intensity is close to 30 emu / g, indicating that the prepared sample has strong magnetism.

[0029] The polarization-electric field (PE) hysteresis loop of the prepared multiferroic heterojunction BaTiO3-CoFe2O4 is shown in Figure 4 , and it can be seen that the remanent polarization is 21.2 μC / cm 2 , indicating that the sample has good ferroelectric polarization.

[0030] Example 2

[0031] The difference from Example 1 is that the amount of BaTiO3 remains unchanged, and the amount of CoFe2O4 is adjusted to 0.001 mol, that is, the molar ratio of BaTiO3 to CoFe2O4 is 1:0.1; others are the same as in Example 1. The prepared product is labeled BTO-0.1CFO.

[0032] Example 3

[0033] The difference from Example 1 is that the amount of BaTiO3 remains unchanged, and the amount of CoFe2O4 is adjusted to 0.002 mol, that is, the molar ratio of BaTiO3 to CoFe2O4 is 1:0.2; others are the same as in Example 1. The prepared product is labeled BTO-0.2CFO.

[0034] Example 4

[0035] The difference from Example 1 is that the amount of BaTiO3 remains unchanged, and the amount of CoFe2O4 is adjusted to 0.005 mol, that is, the molar ratio of BaTiO3 to CoFe2O4 is 1:0.5; others are the same as in Example 1. The prepared product is labeled BTO-0.5CFO.

[0036] The atomic force microscope images of the multiferroic heterojunction BaTiO3-CoFe2O4 prepared in Examples 1-4 are shown in Figure 5 , and it can be seen that the thickness of the prepared samples can meet the requirements of chip devices, and the thickness is controllable: as the content of CoFe2O4 increases, the sample thickness decreases.

Claims

1. A method for preparing a multiferroic heterojunction BaTiO3-CoFe2O4 without substrate support, characterized in that, Here are the steps: (1) BaTiO3 and CoFe2O4 are fully mixed in a molar ratio of 1: (0.1-1), added to water, stirred to obtain a suspension, and then dried to obtain a powder; the powder is sintered at 500-700 ° C for 1-2 h, and cooled in the furnace; (2) Add the sintered powder into 40-60 v% ethanol and stir to obtain a suspension. Then transfer the suspension to a supercritical device and inject carbon dioxide into the supercritical device to make it reach a supercritical state. The stirring reaction time is 3-5 hours. After that, cool to room temperature in air and slowly release the carbon dioxide to relieve the pressure. Separate the suspension after supercritical treatment, take the supernatant, and dry it to obtain a multiferroic heterojunction BaTiO3-CoFe2O4.

2. The method for preparing the substrate-free supported multiferroic heterojunction BaTiO3-CoFe2O4 according to claim 1, wherein: In step (1), the temperature is increased to the sintering temperature at a heating rate of 5-10°C / min.

3. The method for preparing the substrate-free supported multiferroic heterojunction BaTiO3-CoFe2O4 according to claim 1, characterized in that: In step (1), the amount of water used is 40-60 ml for every 0.01 mol BaTiO3.

4. The method for preparing the substrate-free supported multiferroic heterojunction BaTiO3-CoFe2O4 according to claim 1, wherein: In step (2), the mass volume ratio of the sintered powder and ethanol is 60 mg: (40-60) ml.

5. The method for preparing the substrate-free supported multiferroic heterojunction BaTiO3-CoFe2O4 according to claim 1, wherein: In step (2), the supercritical temperature is 80-120°C and the pressure is 10-16 MPa.

6. The method for preparing the substrate-free supported multiferroic heterojunction BaTiO3-CoFe2O4 according to claim 1, wherein: In step (2), the separation method is centrifugal separation.

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