CN104451546A - Preparation method of doped ferrite material with giant plane Hall effect - Google Patents

Abstract

The invention relates to a preparation method of a facing target reactive sputtering epitaxial doped ferric oxide thin film, which adopts a DPS-III type ultra-high vacuum facing target magnetron sputtering coating machine produced by the Shenyang Scientific Instrument Development Center of the Chinese Academy of Sciences. The present invention adopts the technique of direct current reactive magnetron sputtering to the target, and the concentration of Cr doped can be adjusted and controlled by placing different numbers of Cr sheets on the target. Obtaining the giant planar Hall effect We adopt the vertical "four-terminal method" mask, and the obtained planar Hall resistivity can reach the order of 10 ⁵ μΩcm at most. The epitaxial Cr _x Fe _3-x O ₄ thin film preparation method involved in the present invention has the advantages of being compatible with existing industrial production, easy to control doping concentration, simple target selection and high target utilization rate. From Cr _x Fe _3- The giant planar Hall effect obtained in the _x O ₄ thin film enables the optimization of magnetic sensing devices and promotes the development of magnetic sensing devices.

Description

Preparation method of doped ferrite material with giant planar Hall effect

technical field

The patent of the present invention relates to the preparation of doped ferrite and the technology of applying giant planar Hall effect in magnetic sensor devices, more specifically, it is a method of obtaining giant planar Hall effect by doping ferrite a method of

Background technique

The giant planar Hall effect was first discovered in dilute magnetic semiconductor (Ga, Mn) As epitaxial thin film devices in 2003, but the scope of application is only below its Curie temperature of 50K (HXTang, et al, Phys.Rev.B, 2003 ,90,107201). In 2004, a research team discovered the giant planar Hall effect in La _0.84 Sr _0.16 MnO ₃ , but the range where the giant planar Hall effect can be observed is only below 140K (Y.Bason, et al, Appl.Phys. Lett., 2004, 84, 2593), both have a small range of application and cannot be used at room temperature. In 2008, the planar Hall effect measured by the Japanese research team in Fe ₃ O ₄ can reach the order of 10 ⁴ μΩcm at low temperature (A. Fernández-Pacheco, et al, Phys. Rev. B, 2008, 78, 212402 ), the shape of the planar Hall resistivity versus the applied magnetic field is similar to that of the tunnel magnetoresistance TMR. However, increasing the magnitude of the planar Hall resistivity can effectively improve the sensitivity of the magnetic sensor, so that the magnetic sensor device can be optimized. Therefore, obtaining materials with giant planar Hall effect has become a focus of attention. The giant planar Hall effect can not only be used to detect in-plane magnetic anisotropy and magnetization reversal, but also can be used in magnetic sensing devices under low field. Since Fe ₃ O ₄ has a very high Curie temperature of 858K, the giant planar Hall effect can be obtained in a large temperature range by doping, and there is a possibility of replacing TMR in the future, so doping ferrite is a very Good candidate materials open up a broader prospect for the application of magnetic sensors.

_Fe3O4 has a cubic inverse spinel structure at room temperature and standard atmospheric _pressure with a lattice constant of There are 56 ions in a unit cell. Among them, there are 32 oxygen ions, 8 Fe ³⁺ (3d ⁵ , S=5/2) and three adjacent oxygen ions form a tetrahedron, which is called A site. The remaining 8 Fe ²⁺ (3d ⁶ , S=2) and 8 Fe ³⁺ (3d ⁵ , S=5/2) and the adjacent six oxygen ions form an octahedron, which is called the B site. The ions on the sublattice of the A and B sites are ferromagnetically arranged, and the magnetic moments between the A site and the B site are antiferromagnetically arranged through the super exchange of O ^2- , forming ferrimagnetism. For ferrite doping, in general, those with larger ionic radii tend to occupy the B site, while those with smaller ions tend to occupy the A site; while the high-valent ions with larger positive charges tend to occupy the B site, and the smaller positive charges The low-valent ions tend to occupy the A site. If the A site is replaced by a cation with a magnetic moment lower than Fe ³⁺ , or the B site is replaced by a cation with a magnetic moment higher than Fe ³⁺ and Fe ²⁺ , or the gap at the B site is filled with magnetic ions, the ferrite can be improved. The saturation magnetic moment is used to modify the ferrite, and the modification effect is related to the doping amount of the substitute ions. At present, considering the influence of doping on various factors of ferrite, finding suitable doping elements to improve the performance of ferrite and make it better used in spintronic devices has become the focus of attention.

The present invention is based on finding a material that can obtain a larger giant planar Hall effect and has a wider range of applications. On the basis of the known ferrite material with the largest giant planar Hall effect, by doping Cr elements, in order to obtain Larger giant planar Hall effect. After doping Cr element, Cr ³⁺ ions tend to occupy B sites to replace Fe ³⁺ ions. Due to the Cr ³⁺ ion radius Slightly smaller than Fe ³⁺ ion radius Therefore, with the increase of Cr doping amount, the lattice constant of the spinel structure decreases gradually. On the basis of the mature technology of preparing Fe ₃ O ₄ epitaxial thin films in this laboratory, the concentration of Cr element doped is adjusted by placing different numbers of Cr flakes on the Fe target. The advantages of preparation are: by increasing or decreasing the number of Cr flakes, It is easy to obtain Cr _x Fe _3-x O ₄ with different doping concentrations, and the more Cr pieces are placed in the sputtering process, the higher the Cr concentration of the prepared Cr _x Fe _3-x O ₄ samples . And compared with preparation methods such as molecular beam epitaxy and pulsed laser deposition, the magnetron sputtering method is more conducive to meeting the needs of industrial mass production of thin films.

Contents of the invention

From the perspective of industrial production, it is necessary to use the sputtering method and use as simple a target as possible to prepare epitaxially doped Fe ₃ O ₄ thin films. Proceeding from the above two objectives, the present invention develops a method for preparing epitaxial Cr _x Fe _3-x O ₄ thin films by facing target reactive sputtering.

The equipment for reactive sputtering epitaxially doped Fe3O4 thin film of the present invention adopts the DPS-III type ultra-high vacuum facing target magnetron sputtering coating machine produced by the Shenyang Scientific Instrument Development Center of the Chinese Academy of Sciences. The method of reactive sputtering epitaxy of Cr _x Fe _3-x O ₄ thin films to the target has been researched and developed as follows:

1: Preparation of epitaxial Cr _x Fe _3-x O ₄ film

In order to prepare high-quality epitaxial Cr _x Fe _3-x O ₄ thin films, the following key experimental conditions need to be considered during the experiment:

(1) Sputtering power, sputtering power is essentially the rate of film formation, and the size of sputtering power will affect the quality of the film, so choosing an appropriate sputtering power is very important for preparing high-quality epitaxial films;

(2) Sputtering pressure. The sputtering pressure actually determines the total amount of reaction gas that is introduced into the vacuum chamber. We set the flow rate of the reaction gas through the gas flowmeter only to indicate the volume of gas flowing per minute under standard conditions. , so the combination of the setting of the gas flow meter and the setting of the sputtering pressure can determine the total amount of reaction gas passed into the vacuum chamber to ensure that the film has a high epitaxial quality;

(3) Substrate temperature. Experiments have shown that to prepare epitaxial ferrite films with better crystalline quality, the range of experimental conditions is very harsh and narrow, and the required substrate temperature is very demanding;

(4) The ratio of the reaction gas. During the experiment, we need to pass two gases, argon and oxygen, into the vacuum chamber. The main function of argon is to bombard the target, so that the atomic groups on the target splash onto the substrate to deposit a film. ; and the role of oxygen is mainly to react with the Fe atomic groups sputtered from the Fe target and the Cr atomic groups sputtered from the Cr sheet. Selecting an appropriate oxygen partial pressure is to form a pure-phase Cr _x Fe _3-x O ₄ compound key.

The specific technical scheme is as follows:

A method for preparing a doped ferrite material with giant planar Hall effect, the specific operation steps are as follows:

1) Install a pair of Fe targets with a purity of 99.99% on the facing target head of the coating machine, one end as the N pole of the magnetic force line, and the other end as the S pole; the thickness of the target material is 3-5 mm, and the diameter is 60 mm;

2) Cover the polished MgO of the base material with the four-terminal method, install the base on the perpendicular line of the line facing the target, and the vertical distance between the substrate and the line connecting the two Fe targets facing the target is 4-6cm ;

3) Turn on the facing target magnetron sputtering equipment, first use the mechanical pump to draw a first-level vacuum, and then start the molecular pump to draw a second-level vacuum until the vacuum degree of the back and bottom of the sputtering chamber is better than 8×10 ^–6 Pa;

4) Turn on the gas flowmeter for preheating, and adjust the heating current to start heating the substrate until the temperature rises to 450-500°C, then pass in argon gas and turn on the sputtering power supply, clean the impurities on the target surface, and turn off the sputtering power supply ;

5) Introduce sputtering gas argon and oxygen with a purity of 99.999% into the vacuum chamber, first in oxygen, then in argon, wherein the flow rate of argon gas is 100 sccm, and the flow rate of oxygen gas is 0.6-0.8 sccm, the sputtering The vacuum degree of the chamber is kept at 0.5-0.8Pa and is stable;

6) Turn on the sputtering power supply, apply a current of 0.05-0.08A and a DC voltage of 1150-1350V on a pair of Fe targets, pre-sputter for 15-20 minutes, and wait for the sputtering current and voltage to stabilize;

7) Open the baffle plate between the side of the Fe target and the substrate to start sputtering, and the position of the substrate is fixed; during the sputtering process, the temperature of the substrate continues to be maintained;

8) After the sputtering is over, close the baffle between the side of the Fe target and the substrate, then turn off the sputtering power supply, stop feeding the sputtering gas Ar and O ₂ , continue vacuuming, and adjust the temperature control power supply of the substrate to make the sample Decrease to room temperature at a rate of 1-3°C/min, then close the vacuum system, fill the vacuum chamber with nitrogen gas with a purity of 99.999%, open the vacuum chamber, and take out the sample.

The coating machine adopts DPS-III type ultra-high vacuum facing target magnetron sputtering coating machine.

The measuring method of the giant planar Hall effect that the present invention adopts, the steps are as follows:

1) Weld 2-3cm conductive copper wires on the four electrodes of the sample to the sample stage of the multifunctional sample rod, in which the two electrodes in the horizontal direction are connected to the current channel, and the two vertical electrodes are connected to the voltage channel. connected;

2) Before the measurement, install the sample stage with the welded sample on the rotating multifunctional sample rod, apply a magnetic field in the direction parallel to the Cr _x Fe _3-x O ₄ film, and the angle between the magnetic field and the current is determined by rotating the multifunctional sample rod. The sample rod realizes that the direction of the current is changing while the sample is rotating, which means that the angle between the magnetic field and the current is constantly changing, while the direction of the magnetic field remains unchanged;

3) When measuring, the two electrodes connected to the current flow through the current, and the resistance measured in the direction perpendicular to the current is the planar Hall resistance.

If you want to measure the change of the planar Hall resistance with the magnetic field, keep the position of the sample fixed, and change the size of the magnetic field to measure.

To measure the change of the planar Hall resistance with the angle between the magnetic field and the current, set the program to rotate the multifunctional sample rod to change the angle of the sample.

The epitaxial Cr _x Fe _3-x O ₄ thin film preparation method involved in the present invention has the advantages of compatibility with existing industrial production, simple target material selection, and high target material utilization rate. It is used in spintronics such as magnetic information storage and reading. The preparation of related devices has a wide range of application value.

In order to confirm the best embodiment of the present invention, we carried out X-ray diffraction to the film of Cr doping concentration series in the present invention, and used the physical property measurement system to analyze the electrical properties of the film in detail.

Compared with other methods for preparing epitaxial Cr _x Fe _3-x O ₄ films and methods for obtaining planar Hall resistance, the preparation method of the target reactive sputtering epitaxial Cr _x Fe _3-x O ₄ films involved in the present invention It mainly has the following advantages:

1. Compared with the commonly used epitaxial film preparation methods in the laboratory, such as pulsed laser deposition (Pulsed Laser Deposition, PLD) and molecular beam epitaxy (Molecular beam epitaxy, MBE), magnetron sputtering can not only prepare Single crystal epitaxial film with high crystalline quality, under the scanning electron microscope, the prepared epitaxial Cr _x Fe _3-x O ₄ film has no particles or inhomogeneity, the surface of the film is very smooth, and it also occupies a high speed and efficiency. Advantages, compared with the above methods that are only suitable for research in the laboratory, the magnetron sputtering method takes less time to prepare thin films, and is more suitable for the needs of industrial mass production, and it is more convenient and quick to prepare doped samples;

2. To obtain the giant planar Hall effect, the four-terminal mask is used to cover the substrate, and the four-terminal electrodes are formed at one time during the sputtering process. The preparation method is simple and fast, and is suitable for industrial mass production. A magnetic field parallel to the surface of the film is applied during measurement, and planar Hall resistance can be obtained in a direction perpendicular to the current. This method of obtaining electrodes using a vertical four-terminal mask effectively ensures that the direction of the current is strictly perpendicular to the direction of measuring the planar Hall resistance, and eliminates the interference of other factors on the planar Hall resistance.

The preparation method of the facing target reaction sputtering epitaxial doped ferric oxide thin film involved in the present invention has the advantages of being compatible with existing industrial production, easy to control the doping concentration, convenient method of preparing electrodes by "four-terminal method" mask, and target materials. The advantages of simple selection and high target utilization rate, the acquisition of the giant planar Hall effect optimizes the magnetic sensor device, and promotes the development of magnetic sensor devices. The material with the giant planar Hall effect is applied to the spin The preparation of electronic related devices has a wide range of application value.

Description of drawings

Fig. 1(a) is the X-ray diffraction pattern of the epitaxial Cr _x Fe _3-x O ₄ film prepared on the MgO(100) substrate under the condition that the substrate temperature is 500°C in the present invention.

Figure 1(b) shows the variation of the lattice constant of Cr _x Fe _3-x O ₄ with x.

Fig. 1 (c) is x=0, x=0.54, the X-ray of x=0.87 three samples scan diagram.

Fig. 2(a) is the X-ray photoelectron spectrum of the epitaxial Cr _x Fe _3-x O ₄ film prepared on the MgO(100) substrate under the condition that the substrate temperature of the present invention is 500°C.

Fig. 2(b) is the X-ray photoelectron spectrum of the epitaxial Cr _x Fe _3-x O ₄ film prepared on the MgO(100) substrate under the condition that the substrate temperature of the present invention is 500°C.

Figure 3(a) shows the relationship between the in-plane Hall resistivity of the epitaxial Cr _0.97 Fe _0.03 O ₄ thin film prepared on the MgO(100) substrate with the angle between the magnetic field and the current at a substrate temperature of 500°C according to the present invention.

Figure 3(b) shows the variation of the planar Hall resistivity of the sample Cr _0.97 Fe _0.03 O ₄ with the magnetic field.

Figure 4(a) shows the relationship between the in-plane Hall resistivity of the epitaxial Cr _0.64 Fe _0.54 O ₄ thin film prepared on the MgO(100) substrate at different temperatures with the angle between the magnetic field and the current at a substrate temperature of 500°C in the present invention .

Figure 4(b) shows the relationship between the planar Hall resistivity and the Cr doping amount at different temperatures.

Figure 5(a) shows the difference in longitudinal resistivity at different temperatures for the preparation of epitaxial Cr _x Fe _3-x O ₄ films on MgO(100) substrates at a substrate temperature of 500°C in the present invention Δρ _xx ^jump = ρ _// -Dependence of ρ _⊥ on Cr doping content.

Figure 5(b) shows the ratio of ρ _xy and Δρ _xx ^jump with Cr doping content at different temperatures for the preparation of epitaxial Cr _x Fe _3-x O ₄ thin films on MgO(100) substrates at a substrate temperature of 500°C in the present invention alternative relation.

Detailed ways

According to the structure and property analysis that we carry out to the sample prepared in the present invention, the preparation method of the epitaxial doping ferric oxide thin film to the target reaction sputtering will be described in detail as follows:

1. The DPS-III ultra-high vacuum facing target magnetron sputtering coating machine produced by the Shenyang Scientific Instrument Development Center of the Chinese Academy of Sciences is used. A pair of Fe targets with a purity of 99.99% are installed on the facing target heads. Two target heads One for each, one end as the N pole of the magnetic force line, and the other end as the S pole, and then put different numbers of Cr sheets on the surface of the lower target to control the concentration of Cr doping. The thickness of the target is 3mm and the diameter is 60mm;

2. After removing surface impurities from the polished MgO base material by means of ultrasonic waves, etc., cover the base with a four-terminal mask so that the four electrodes required for measuring the planar Hall resistivity can be obtained during the sputtering process, and then The substrate is installed on the vertical line of the line facing the target, and the vertical distance between the substrate and the line connecting the two Fe targets facing the target is 4-6cm;

3. Turn on the DPS-III facing target magnetron sputtering equipment, first start the mechanical pump to draw a first-level vacuum until the vacuum degree is below 20Pa, which meets the working conditions of the molecular pump, and then start the molecular pump to draw a second-level vacuum until the sputtering The back vacuum of the injection chamber is better than 8×10 ^–6 Pa;

4. Turn on the gas flow meter for preheating (20-30 minutes), turn on the substrate heating power supply at the same time, adjust the heating current, so that the substrate temperature rises to 450-500°C, and after 20-30 minutes, feed 100 sccm of pure argon, Adjust the air pressure at about 1-3Pa, turn on the sputtering power supply, apply a current of 0.05-0.08A and a DC voltage of 1150-1350V to the Fe target, clean the impurities and oxide layer on the target surface, and turn off the sputtering power supply after 5-7 minutes ;

5. After step 4 is finished, feed the sputtering gas argon and oxygen with a purity of 99.999% into the vacuum chamber. The flow rate of the argon gas is 100 sccm, and the flow rate of oxygen is 0.6-0.8 sccm. Oxygen in order to avoid the large flow of argon deposited in the gas mixing chamber and hinder the entry of oxygen. Keep the vacuum degree of the sputtering chamber at 0.5-0.8Pa, and keep it stable for 3-5 minutes;

6. Turn on the sputtering power supply, apply a current of 0.05-0.08A and a DC voltage of 1150-1350V on a pair of Fe targets, pre-sputter for 15-20 minutes, and wait for the sputtering current and voltage to stabilize;

7. Open the baffle between the side of the Fe target and the substrate to start sputtering, and the position of the substrate is fixed. During the sputtering process, the substrate temperature continues to be maintained;

8. After the sputtering is over, close the baffle between the side of the Fe target and the substrate, then turn off the sputtering power supply, stop feeding the sputtering gas Ar and O ₂ , continue vacuuming, and adjust the temperature control power supply of the substrate to make the sample Decrease to room temperature at a rate of 1-3°C/min, then close the vacuum system, fill the vacuum chamber with nitrogen gas with a purity of 99.999%, open the vacuum chamber, and take out the sample.

Two: Acquisition of giant planar Hall effect

We use a measurement system designed by Quantum Design Company in the United States that can achieve different measurement purposes: Physical Property Measurement System (PPMS) to measure planar Hall resistivity.

1. Grind the copper wire with sandpaper until the oxide layer is completely worn off, measure with a multimeter to ensure that the copper wire is conductive, and then cut the copper wire into 2-3cm long sections for welding the sample on the sample stage.

2. Weld the copper wires on the four electrodes of the sample to the sample stage of the multifunctional sample rod with an electric soldering iron, in which the two electrodes in the horizontal direction are connected to the current channel, and the two vertical electrodes are connected to the voltage channel.

3. Before the measurement, install the sample stage with the welded sample on the rotatable multifunctional sample rod, and apply a magnetic field in the direction parallel to the Cr _x Fe _3-x O ₄ film. The angle change between the magnetic field and the current is determined by The rotation of the multi-function sample rod is realized, and the direction of the current is also changing while the sample is rotating, which is equivalent to the constant change of the angle between the magnetic field and the current, while the direction of the magnetic field remains unchanged.

4. When measuring, the two electrodes connected to the current will pass through the current, and the resistance measured in the direction perpendicular to the current is the planar Hall resistance. If you want to measure the change of the planar Hall resistance with the magnetic field, keep the position of the sample fixed, and change the size of the magnetic field to measure; if you want to measure the change of the planar Hall resistance with the angle between the magnetic field and the current, set the program to rotate the multifunctional sample rod , just change the angle of the sample.

Figure 1(a) is the X-ray diffraction pattern of the epitaxial Cr _x Fe _3-x O ₄ film prepared on the MgO(100) substrate under the substrate temperature of 500°C in the present invention; as can be seen from the figure, only The peak of (00l) orientation of ferrite was found, indicating that the crystal structure of ferrite was not changed after the addition of Cr element.

Figure 1(b) shows the variation of the lattice constant of Cr _x Fe _3-x O ₄ with x. It can be seen from the figure that the lattice constant decreases after the incorporation of Cr is due to the Cr ³⁺ ion radius Slightly smaller than Fe ³⁺ ion radius

Fig. 1 (c) is x=0, x=0.54, the X-ray of x=0.87 three samples scans; from x-rays It can be seen in the scanning image that the four diffraction peaks are uniformly spaced at 90°, which reflects the four-fold symmetry of the cubic crystal system and proves the epitaxial relationship of the Cr _x Fe _3-x O ₄ film.

Figure 2(a) is the X-ray photoelectron spectrum of the epitaxial Cr _x Fe _3-x O ₄ thin film prepared on the MgO(100) substrate under the condition of the substrate temperature of the present invention at 500°C, the X-ray photoelectron spectrum and valence state of Fe analyze. It is reflected in the figure that Fe ions are mainly expressed as Fe ²⁺ and Fe ³⁺ .

Figure 2(b) is the X-ray photoelectron spectrum of the epitaxial Cr _x Fe _3-x O ₄ thin film prepared on the MgO(100) substrate under the condition of the substrate temperature of the present invention at 500°C, the X-ray photoelectron spectrum and valence state of Cr analyze. The figure shows that Cr ions are mainly represented as Cr ²⁺ and Cr ³⁺ .

Figure 3(a) shows the relationship between the in-plane Hall resistivity of the epitaxial Cr _0.97 Fe _0.03 O ₄ film prepared on the MgO(100) substrate with the angle between the magnetic field and the current at a substrate temperature of 500°C; It can be seen that the planar Hall resistivity increases with the increase of the applied magnetic field.

Figure 3(b) shows the variation of the planar Hall resistivity of the sample Cr _0.97 Fe _0.03 O ₄ with the magnetic field. It can be seen from the figure that the sign of the planar Hall resistivity is just opposite when the angle between the magnetic field and the current is 45° and 135°.

Figure 4(a) shows the relationship between the in-plane Hall resistivity of the epitaxial Cr _0.64 Fe _0.54 O ₄ thin film prepared on the MgO(100) substrate at different temperatures with the angle between the magnetic field and the current at a substrate temperature of 500°C in the present invention , it can be seen that the planar Hall resistivity decreases with increasing temperature.

Figure 4(b) shows the relationship between the planar Hall resistivity and the Cr doping amount at different temperatures. It can be seen from the figure that the largest planar Hall resistivity is about 10 ⁵ μΩcm, which appears in the 150K Cr _0.29 Fe _0.71 O ₄ sample.

Figure 5(a) shows the difference in longitudinal resistivity at different temperatures for the preparation of epitaxial Cr _x Fe _3-x O ₄ films on MgO(100) substrates at a substrate temperature of 500°C in the present invention Δρ _xx ^jump = ρ _// -Dependence of ρ _⊥ on Cr doping content. The sign change occurs at x=0.54, which reflects the sign of the AMR ratio from positive to negative with the increase of Cr content.

Figure 5(b) shows the ratio of ρ _xy and Δρ _xx ^jump with Cr doping content at different temperatures for the preparation of epitaxial Cr _x Fe _3-x O ₄ thin films on MgO(100) substrates at a substrate temperature of 500°C in the present invention alternative relation. Its ratio increases with the increase of Cr doping; it can be seen that the ratio of planar Hall resistivity to longitudinal resistivity is small, proving the fact that the planar Hall effect has the same source as the anisotropic magnetoresistance , which also demonstrates the accuracy of planar Hall resistivity measurements.

Claims (5)

1. A method for preparing a doped ferrite material with giant plane Hall effect, characterized in that the steps of operation are as follows: 1) Install a pair of Fe targets with a purity of 99.99% on the facing target head of the coating machine, one end as the N pole of the magnetic force line, and the other end as the S pole; the thickness of the target material is 3-5 mm, and the diameter is 60 mm; 2) Cover the polished MgO of the base material with the four-terminal method, install the base on the perpendicular line of the line facing the target, and the vertical distance between the substrate and the line connecting the two Fe targets facing the target is 4-6cm ; 3) Turn on the facing target magnetron sputtering equipment, first use the mechanical pump to draw a first-level vacuum, and then start the molecular pump to draw a second-level vacuum until the vacuum degree of the back and bottom of the sputtering chamber is better than 8×10 ^–6 Pa; 4) Turn on the gas flowmeter for preheating, and adjust the heating current to start heating the substrate until the temperature rises to 450-500°C, then pass in argon gas and turn on the sputtering power supply, clean the impurities on the target surface, and turn off the sputtering power supply ; 5) Introduce sputtering gas argon and oxygen with a purity of 99.999% into the vacuum chamber, first in oxygen, then in argon, wherein the flow rate of argon gas is 100 sccm, and the flow rate of oxygen gas is 0.6-0.8 sccm, the sputtering The vacuum degree of the chamber is kept at 0.5-0.8Pa and is stable; 6) Turn on the sputtering power supply, apply a current of 0.05-0.08A and a DC voltage of 1150-1350V on a pair of Fe targets, pre-sputter for 15-20 minutes, and wait for the sputtering current and voltage to stabilize; 7) Open the baffle plate between the side of the Fe target and the substrate to start sputtering, and the position of the substrate is fixed; during the sputtering process, the temperature of the substrate continues to be maintained; 8) After the sputtering is over, close the baffle between the side of the Fe target and the substrate, then turn off the sputtering power supply, stop feeding the sputtering gas Ar and O ₂ , continue vacuuming, and adjust the temperature control power supply of the substrate to make the sample Decrease to room temperature at a rate of 1-3°C/min, then close the vacuum system, fill the vacuum chamber with nitrogen gas with a purity of 99.999%, open the vacuum chamber, and take out the sample. 2. The method according to claim 1, characterized in that the coating machine adopts a DPS-III type ultra-high vacuum magnetron sputtering coating machine for the target. 3. A method for measuring the giant planar Hall effect, characterized in that the steps are as follows: 1) Weld 2-3cm conductive copper wires on the four electrodes of the sample to the sample stage of the multifunctional sample rod, in which the two electrodes in the horizontal direction are connected to the current channel, and the two vertical electrodes are connected to the voltage channel. connected; 2) Before the measurement, install the sample stage with the welded sample on the rotating multifunctional sample rod, apply a magnetic field in the direction parallel to the Cr _x Fe _3-x O ₄ film, and the angle between the magnetic field and the current is determined by rotating the multifunctional sample rod. The sample rod realizes that the direction of the current is changing while the sample is rotating, which means that the angle between the magnetic field and the current is constantly changing, while the direction of the magnetic field remains unchanged; 3) When measuring, the two electrodes connected to the current flow through the current, and the resistance measured in the direction perpendicular to the current is the planar Hall resistance. 4. The method according to claim 3, characterized in that measuring the variation of the planar Hall resistance with the magnetic field, keeping the position of the sample fixed, and changing the size of the magnetic field to measure. 5. The method according to claim 3, characterized in that the measurement of the planar Hall resistance varies with the angle between the magnetic field and the current, and the program is set to rotate the multifunctional sample rod to change the angle of the sample.