CN115340088A - Temperature-independent linear magneto-resistor material and preparation method and application thereof - Google Patents
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Abstract
The invention discloses a linear magneto-resistance material independent of temperature, a preparation method and application thereof. Under the condition of a magnetic field of 9T, the Magnetoresistance (MR) of the graphite film material at 2K is 96%, and the MR at 300K reaches 118%. Based on the characteristics, the graphite film obtained by the invention can be widely applied to the preparation of various magnetic sensors, and based on the linear response that the magnetic resistance of the graphite film does not depend on the temperature, the prepared graphite film magnetic sensor can realize the measurement of high precision and wide temperature zone, and is particularly suitable for the measurement of strong magnetic field.
Description
Technical Field
The invention belongs to the technical field of magneto-resistance materials, and particularly relates to a linear magneto-resistance material independent of temperature and a preparation method and application thereof.
Background
In 1833, the first kelvin of scientists in the united states discovered that the resistance of a conductor changes under the action of a magnetic field. Subsequently, it was found that the resistivity of some metals or semiconductors increases with increasing magnetic field, and this phenomenon is called magnetoresistance effect. The semiconductor magnetoresistance effect is divided into two categories, one is the magnetoresistance effect of the material itself, calledThe physical magnetoresistance effect; the other type is that the resistance increasing rate is different under the same magnetic field action due to the different shape and structure of the semiconductor, and the magnetoresistance effect related to the shape and the size of the semiconductor is called geometric magnetoresistance effect. We define the change in resistance as
Wherein R (H) is the resistance under the external magnetic field H, and R (0) is the resistance when the external magnetic field is 0.
The application of the magnetoresistance effect is quite extensive, and the common magnetoresistance effects are divided into four types: giant magnetoresistance effect (GMR), giant magnetoresistance effect (CMR), tunnel magnetoresistance effect (TMR), anisotropic magnetoresistance effect (AMR). The giant magnetoresistance effect is a characteristic that the magnetoresistance R of some magnetic or alloy materials sharply decreases under a certain magnetic field, and Δ R/R sharply increases, and generally the increase is about 10 times higher than the magnetoresistance of general magnetic or alloy materials. The sensor made using this effect is called a GMR sensor. The GMR effect is a quantum mechanical and agglomeration physics phenomenon that can be observed in thin film (a few nanometers thick) structures where magnetic and non-magnetic materials are interspersed. The GMR effect has been widely used in high-density read heads and magnetic memory elements. However, the saturation magnetic field of the ordinary GMR material is small, and the GMR material can only be used for measuring weak magnetic field generally. The giant magnetoresistance effect is a physical phenomenon of agglomerates, which means that the resistance of a material in a magnetic field is significantly reduced. The magnetoresistance of the supermagnet effect varies by several orders of magnitude with the applied magnetic field. Because of its low phase transition temperature, unlike giant magnetoresistive materials, which exhibit their properties at room temperature, there is a certain distance from practical applications.
The measurement/detection of magnetic fields is of great technical significance, and various types of magnetic field sensors have been developed. It is clear that the magnetoresistive effect can be used for this purpose, and magnetoresistive sensors based on the AMR effect have been widely used for measuring or detecting magnetic fields for decades. In present day hard disk drives, the read head uses almost entirely the principle of giant magnetoresistance, utilizing a so-called spin valve structure. The 1997 introduction made it possible to keep the magnetic storage density increasing further at a high rate, and the GMR performance guaranteed this trend to continue even in the future. MR is expected to have great potential for application in magnetic field measurements, magnetoresistive sensors and magnetic storage. There have been studies to find giant magnetoresistance effects in graphite and graphite-based materials.
Generally, MR in conventional metals is less than a few percent, negligible, and reaches saturation at high magnetic fields. In the last decades, in zero band gap semiconductors such as Ag 2±δ Se、Ag 2±δ Te, inSb, multilayer graphene, topological crystalline insulator, topological insulator and Dirac material Cd 3 As 2 A linearly dependent magnetoresistance (LMR) is observed, i.e. the resistance increases linearly with increasing magnetic field. Most of the materials have larger differences of magnetoresistance at different temperatures: the magneto-resistance is very large at low temperature, and the magneto-resistance value is smaller at high temperature. When the material is applied to some magnetic sensors, the accuracy of the sensors is reduced because of the high temperature environment.
CN112938961A device and method for preparing graphite by on-line catalytic reduction method adopts the most common H 2 The Fe catalytic reduction method is used for preparing the device for on-line catalysis of graphitization of the water body sample. The device abandons the traditional method of using a vacuum system to extract CO in a sample 2 In a designed closed gas circuit, a helium gas is used for blowing an acidified sample, and blown CO is used 2 Purifying the gas to remove impurities, introducing the gas into a catalytic reduction tube, and purifying the gas in the presence of H 2 And reducing the graphite carbon into graphite carbon under the action of iron powder. Can avoid the atmosphere to reveal effectively, stain to graphitizing sample, can purify the produced volatile gaseous impurity of water sample simultaneously, avoid the inefficacy of catalyst and reductant. By controlling H 2 The flow rate, the He flow rate, the reaction acidification temperature, the iron powder content and the temperature of the reaction furnace are used for controlling the reaction process of graphitization. By discharging CO from gas 2 And CH 4 And (4) detecting the content, and judging the completion progress of the graphitization reaction. However, the reaction apparatus is complicated and difficult to operate, thereby limiting the yield; the reaction needs to be carried out under the condition of high temperature, the required time is longer,moreover, the reaction conditions are very high, so that the production cost is relatively high, and the method is not suitable for large-scale production and application.
Disclosure of Invention
In order to solve the problems in the existing materials, the invention provides a linear magneto-resistance material independent of temperature, a preparation method and application thereof. The material is composed of graphite film, and the magneto-resistance effect of the material has good linearity at low temperature and normal temperature and basically does not change along with temperature.
In order to realize the purpose, the technical scheme adopted by the invention is as follows:
a method for preparing a linear magneto-resistance material independent of temperature comprises the following steps:
s1: adding amorphous graphite into concentrated sulfuric acid, and stirring to obtain a mixed solution; then adding KMnO 4 Stirring, wherein all stirring processes are carried out under an ice bath condition; transferring the mixed solution into a water bath, and slowly adding KNO into the mixed solution 3 And stirring; then, continuously adding deionized water into the mixed solution, transferring the mixed solution into an oil bath and stirring;
s2: will H 2 O 2 Adding the mixture into the mixed solution obtained in the step S1, and continuing to react until the solution is changed from dark brown to bright yellow; adding a mixed solution of hydrazine hydrate and polyvinylpyrrolidone (PVP) into the bright yellow mixed solution for reaction; adding a reducing agent into the mixed solution after reaction to obtain black powder, sequentially washing the powder with water and ethanol, centrifuging and drying;
s3: and adding the dried powder into a mould, and carrying out mould pressing to obtain a graphite film, namely the linear magnetoresistance material independent of temperature.
Further, in the step S1, the purity of the amorphous graphite is 99%, and the mass-volume ratio of the amorphous graphite to concentrated sulfuric acid is 0.005-0.1 g/mL; adding amorphous graphite into concentrated sulfuric acid, and stirring for 20-40 min.
Further, in step S1, KMnO 4 The mass ratio of the graphite to the amorphous graphite is 4-8; adding KMnO 4 The stirring time is 20-40 min.
Further, in step S1,KNO 3 the mass ratio of the graphite to the amorphous graphite is 6-10; adding KNO into the mixed solution 3 The stirring time is 40-80 min, and the water bath temperature is 10-30 ℃.
Further, in the step S1, the mass-to-volume ratio of the amorphous graphite to the deionized water is 0.01-0.017 g/mL; transferring the mixed solution into an oil bath, and stirring for 20-40 min at the temperature of 60-100 ℃.
Further, in step S2, amorphous graphite and H 2 O 2 The mass-to-volume ratio of (A) is 0.1-0.125 g/mL; the continuous reaction time is 40-80 min.
Further, in step S2, the volume ratio of the hydrazine hydrate to the PVP mixed solution is V Nitrile hydrate ∶V PVp =2:1, wherein the mass concentration of PVP is 1-15 wt%; the hydrazine hydrate and PVP mixed solution is added into the bright yellow mixed solution for reaction for 30-120 min at the temperature of 40-80 ℃.
Further, in step S2, the reducing agent is acetic acid or hydroiodic acid; the amount added was 20mL.
Further, in the step S2, the drying temperature is 40-60 ℃, and the drying time is 12-36 h.
Further, in step S3, the molding conditions are: the pressure is 1-10 Mpa, the temperature is 800-950 ℃, and the vacuum degree is less than 0.1Mpa.
The invention also provides a linear magneto-resistance material which is prepared by the preparation method and does not depend on temperature.
The linear magneto-resistance material independent of temperature obtained by the invention can be widely applied to preparation of various magnetic sensors. Based on the linear response that the magnetic resistance of the sensor does not depend on the temperature, the prepared magnetic sensor can realize the measurement of high precision and wide temperature zone, and is particularly suitable for the measurement of strong magnetic field.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) Compared with the preparation of other magneto-resistance materials, the preparation method has the advantages of lower cost, simple required equipment and more convenient manufacturing process.
(2) The magnetic resistance of the material prepared by the invention is hardly influenced by temperature, and the material has better linear response from 2K to 300K. The material has 96% of Magnetoresistance (MR) at 2K and 118% of MR at 300K under the condition of a magnetic field of 9T.
(3) The resistivity of the carbon film prepared by the invention is about 0.05m omega cm, the linear magnetoresistance can be measured when the current is 100 muA, and the power is about 5 multiplied by 10 -9 W, the device prepared by the invention has low power consumption and saves more energy.
Drawings
FIG. 1 is a schematic diagram of devices made of the magneto-resistive material prepared by the present invention in different shapes and sizes, where the size unit is cm.
Fig. 2 is a raman spectrum of graphite films of different thicknesses obtained in example 1.
Fig. 3 is an XRD diffraction pattern of graphite films of different thicknesses obtained in example 1.
FIG. 4 shows the MR curves of the 0.1mm graphite film obtained in example 1 at different temperatures, with the scanning interval of the magnetic field being-9T to 9T.
FIG. 5 shows the MR curves of the 0.01mm graphite film obtained in example 1 at different temperatures, with the scanning interval of the magnetic field being-9T to 9T.
Detailed Description
The following further describes embodiments of the present invention in conjunction with the following examples and figures, but the practice of the present invention is not limited thereto.
Example 1
A method for preparing a linear magneto-resistive material independent of temperature comprises the following steps:
s1: adding 2g of amorphous graphite with the purity of 99% into 50mL of concentrated sulfuric acid, stirring for 20min, and carrying out the whole stirring process under an ice bath condition; mixing 8g of KMnO 4 Adding into the above mixed solution and stirring for 20min, wherein the stirring process is carried out under ice bath condition; transferring the mixed solution to a water bath at 10 ℃, and adding 12g KNO into the mixed solution 3 And stirred for 40min; continuously adding 200mL of deionized water into the mixed solution, transferring the mixed solution into an oil bath at 80 ℃ and stirring for 30min;
s2: 20mL of H 2 O 2 Dropwise adding the mixture obtained in the step S1, and continuing to react for 50min until the solution turns from dark brown to bright yellow; 10mL of hydrazine hydrate was mixed with PVP (10 wt% PVP Nitrile hydrate ∶V PVP =2: 1) adding the mixed solution into a bright yellow mixed solution, and reacting for 1h at 40 ℃; adding 20mL of acetic acid into the mixed solution obtained after the reaction in the last step to obtain black powder, washing the powder with water, centrifuging the powder for several times, washing the powder with ethanol for one time, and drying the powder at 50 ℃ for 24 hours;
s3: adding 1.5g of the dried powder into a mold, and molding for 30min under the conditions of 5MPa of pressure, 850 ℃ of temperature and 0.05MPa of vacuum degree to obtain the graphite film.
As shown in FIG. 1, the magneto-resistive material prepared by the present invention can be prepared into devices of various sizes and shapes, FIG. 1 (a) is a hall-bar made of the graphite film obtained in example 1, which has a resistivity of about 0.05 m.OMEGA.cm, and can detect linear magnetoresistance at a current of 100. Mu.A, and a power of about 5X 10 -9 W is added. Fig. 1 (b) is a schematic view of another device made of the material, which has a circular ring shape.
Fig. 2 is a raman spectrum of the graphite film obtained in example 1 at three different thicknesses of 0.03mm, 0.05mm and 0.1mm, and it can be seen that characteristic peaks of carbon are evident, indicating that the purity of the sample is relatively high. The D peak in the raman spectrum represents a defect of a lattice of C atoms, and the G peak represents in-plane stretching vibration of sp2 hybridization of C atoms. That is, the relative intensity of the D peak reflects the degree of disorder of the crystal structure, the G peak represents the sp2 bond structure of C, the D/G intensity ratio can be used to characterize the degree of disorder of graphite, and Raman analysis can determine that the degree of disorder of the graphite film obtained in example 1 is very low. FIG. 3 is an XRD diffractogram of the graphite film obtained in example 1 at three different thicknesses of 0.03mm, 0.05mm and 0.1mm, and a weak broad peak located at about 23 degrees is provided in addition to two (002) and (004) crystal plane diffractograms, which may be caused by nanocrystals in the sample. Fig. 2 and 3 show that the graphite flake prepared by the method of the present invention is a polycrystalline material with a high degree of orientation.
The graphite film obtained in example 1 was cut into rectangular graphite sheets of 5mm × 10mm × 0.1mm with a diamond knife, and the magnetoresistance of the graphite film at 2K, 10K, 100K, 200K, and 300K was measured by the four-electrode method, with the scanning interval of the magnetic field being-9T to 9T and the electrode spacing being 3mm, to obtain the magnetoresistance MR curve of the material, and as shown in fig. 4, the magnetoresistance of the material hardly changed with temperature, was 118% at room temperature and was in a linear relationship with the magnetic field, had high sensitivity to the change in the magnetic field, and was used for high-precision magnetic field measurement. The magnetic resistance of the graphite film obtained in example 1 was measured by cutting it with a diamond knife into rectangular graphite sheets of 5mm × 10mm × 0.01mm in the same manner as described above, and as shown in fig. 5, the magnetic resistance material after sintering at 300K under vacuum hot pressing had an MR of 118% at room temperature and an MR of 96% at 2K, and it was possible to maintain a good linear response of MR to the external magnetic field H in a plurality of temperature ranges, substantially without temperature changes.
Example 2
A method for preparing a linear magneto-resistance material independent of temperature comprises the following steps:
s1: adding 2g of amorphous graphite with the purity of 99% into 100mL of concentrated sulfuric acid, stirring for 30min, and carrying out the whole stirring process under an ice bath condition; 10g of KMnO 4 Adding into the above mixed solution and stirring for 30min, wherein the stirring process is carried out under ice bath condition; transferring the mixed solution to a water bath at 20 ℃, and adding 20g KNO into the mixed solution 3 And stirring for 60min; continuously adding 200mL of deionized water into the mixed solution, transferring the mixed solution into an oil bath at 80 ℃ and stirring for 20min;
s2: 20mL of H 2 O 2 Dropwise adding the mixture into the mixed solution obtained in the step S1, and continuously reacting for 60min until the solution is changed from dark brown to bright yellow; 20mL of hydrazine hydrate was mixed with PVP (10 wt% PVP Nitrile hydrate ∶V PVP =2: 1) adding the mixed solution into a bright yellow mixed solution to react for 30min at 60 ℃; adding 20mL of acetic acid into the mixed solution obtained after the reaction in the previous step to obtain black powder, washing the powder with water, centrifuging the powder for several times, washing the powder with ethanol once, and drying the powder at 50 ℃ for 24 hours.
S3: adding 1g of the dried powder into a mold, and molding for 10min under the conditions of 10MPa of pressure, 850 ℃ of temperature and 0.05MPa of vacuum degree to obtain the graphite film.
Example 3
A method for preparing a linear magneto-resistance material independent of temperature comprises the following steps:
s1: adding 2g of amorphous graphite with the purity of 99% into 200mL of concentrated sulfuric acid, stirring for 40min, and carrying out the whole stirring process under an ice bath condition; 14g of KMnO 4 Adding into the above mixed solution and stirring for 40min, wherein the stirring process is carried out under ice bath condition; transferring the mixed solution into a water bath at 30 ℃, and adding 20g of KNO into the mixed solution 3 And stirred for 80min; 120mL of deionized water was continuously added to the above mixture, and the mixture was transferred to a 100 ℃ oil bath and stirred for 40min.
S2: 16mL of H 2 O 2 Dropwise adding the mixture into the mixed solution obtained in the step S1, and continuing to react for 80min until the solution turns from dark brown to bright yellow; 40mL of hydrazine hydrate was mixed with PVP (10 wt% PVP Nitrile hydrate ∶V PVP =2: 1) adding the mixed solution into a bright yellow mixed solution to react for 2h at the temperature of 80 ℃; 20mL of hydroiodic acid was added to the mixture after the previous reaction to obtain a black powder, which was washed several times with water, washed once with ethanol, and dried at 50 ℃ for 24 hours.
S3: adding 1g of the dried powder into a mold, and carrying out mold pressing for 20min under the conditions of the pressure of 10MPa, the temperature of 950 ℃ and the vacuum degree of 0.05MPa to obtain the graphite film.
Example 4
A method for preparing a linear magneto-resistive material independent of temperature comprises the following steps:
s1: adding 2g of amorphous graphite with the purity of 99% into 100mL of concentrated sulfuric acid, stirring for 40min, and carrying out the whole stirring process under an ice bath condition; 16g of KMnO 4 Adding into the above mixed solution and stirring for 30min, wherein the stirring process is carried out under ice bath condition; transferring the mixed solution into a water bath at 20 ℃, and adding 15g KNO into the mixed solution 3 And stirring for 60min; continuously adding 200mL of deionized water into the mixed solution, transferring the mixed solution into an oil bath at 80 ℃ and stirring for 20min;
s2: 20mL of H 2 O 2 Dropwise adding the mixture into the mixed solution obtained in the step S1, and continuously reacting for 60min until the solution is changed from dark brown to bright yellow; 20mL of hydrazine hydrate and PVP (10 wt% PVP Nitrile hydrate ∶V PVP =2: 1) adding the mixed solution into a bright yellow mixed solution, and reacting for 30min at 60 ℃; adding 20mL of acetic acid into the mixed solution obtained after the reaction in the previous step to obtain black powder, washing the powder with water, centrifuging for several times, washing with ethanol once, and drying at 60 ℃ for 36h.
S3: adding 1g of the dried powder into a mold, and carrying out mold pressing for 10min under the conditions of the pressure of 10MPa, the temperature of 850 ℃ and the vacuum degree of 0.05MPa to obtain the graphite film.
Example 5
A method for preparing a linear magneto-resistance material independent of temperature comprises the following steps:
s1: adding 2g of amorphous graphite with the purity of 99% into 400mL of concentrated sulfuric acid, stirring for 20min, and carrying out the whole stirring process under an ice bath condition; 16g of KMnO 4 Adding into the above mixed solution and stirring for 30min, wherein the stirring process is carried out under ice bath condition; transferring the mixed solution to a water bath at 30 ℃, and adding 18g KNO into the mixed solution 3 And stirring for 60min; continuously adding 200mL of deionized water into the mixed solution, transferring the mixed solution into an oil bath at 60 ℃ and stirring for 20min;
s2: 20mL of H 2 O 2 Dropwise adding the mixture into the mixed solution obtained in the step S1, and continuously reacting for 60min until the solution is changed from dark brown to bright yellow; 20mL of hydrazine hydrate and PVP (10 wt% PVP Nitrile hydrate ∶V PVP =2: 1) adding the mixed solution into a bright yellow mixed solution to react for 30min at 60 ℃; adding 20mL of acetic acid into the mixed solution obtained after the reaction in the previous step to obtain black powder, washing the powder with water, centrifuging the powder for several times, washing the powder with ethanol once, and drying the powder at the temperature of 40 ℃ for 12 hours.
S3: adding 1g of the dried powder into a mold, and molding for 10min under the conditions of 10MPa of pressure, 850 ℃ of temperature and 0.05MPa of vacuum degree to obtain the graphite film.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (10)
1. A method for preparing a linear magneto-resistance material independent of temperature is characterized by comprising the following steps:
s1: adding amorphous graphite into concentrated sulfuric acid, and stirring to obtain a mixed solution; then adding KMnO 4 Stirring, wherein all stirring processes are carried out under an ice bath condition; transferring the mixed solution into a water bath, and adding KNO into the mixed solution 3 And stirring; then, continuously adding deionized water into the mixed solution, transferring the mixed solution into an oil bath and stirring;
s2: h is to be 2 O 2 Adding the mixture into the mixed solution obtained in the step S1, and continuously reacting until the solution is changed from dark brown to bright yellow; adding a mixed solution of hydrazine hydrate and PVP into the bright yellow mixed solution for reaction; adding a reducing agent into the mixed solution after the reaction to obtain black powder, sequentially washing the powder with water and ethanol, centrifuging and drying;
s3: and adding the dried powder into a mould, and carrying out mould pressing to obtain a graphite film, namely the linear magneto-resistance material independent of temperature.
2. The method for preparing a linear magnetoresistance material independent of temperature according to claim 1, wherein in step S1, the mass-to-volume ratio of amorphous graphite to concentrated sulfuric acid is 0.005 to 0.1g/mL; adding amorphous graphite into concentrated sulfuric acid and stirring for 20-40 min; KMnO 4 The mass ratio of the graphite to the amorphous graphite is 4-8; adding KMnO 4 The stirring time is 20-40 min.
3. The method for preparing a linear magnetoresistive material independent of temperature as claimed in claim 1, wherein in step S1, KNO 3 With amorphous graphiteThe mass ratio is 6-10; adding KNO into the mixed solution 3 Stirring for 40-80 min, and heating in water bath at 10-30 deg.c; the mass-volume ratio of the amorphous graphite to the deionized water is 0.01-0.017 g/mL; transferring the mixed solution into an oil bath and stirring for 20-40 min, wherein the temperature of the oil bath is 60-100 ℃.
4. The method according to claim 1, wherein in step S2, amorphous graphite is mixed with H 2 O 2 The mass volume ratio of the (A) is 0.1-0.125 g/mL; the continuous reaction time is 40-80 min.
5. The method according to claim 1, wherein in step S2, the volume ratio of hydrazine hydrate to PVP mixed solution is V Nitrile hydrate ：V PVP =2:1, wherein the mass concentration of PVP is 1-15 wt%; the hydrazine hydrate and PVP mixed solution are added into the bright yellow mixed solution for reaction for 30-120 min at the temperature of 40-80 ℃.
6. The method according to claim 1, wherein the reducing agent is acetic acid or hydroiodic acid in step S2.
7. The method for preparing a linear magneto-resistive material independent of temperature according to claim 1, wherein in step S2, the drying temperature is 40 to 60 ℃ and the drying time is 12 to 36 hours.
8. The method of claim 1, wherein in step S3, the molding conditions are as follows: the pressure is 1-10 Mpa, the temperature is 800-950 ℃, and the vacuum degree is less than 0.1Mpa.
9. A linear magnetoresistive material independent of temperature produced by the production method according to any one of claims 1 to 8.
10. Use of a linear magnetoresistive material according to claim 9 that is temperature independent for the manufacture of a magnetic sensor.
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