CN108922709B

CN108922709B - Demagnetization-resistant functionally-graded permanent magnet material and preparation method thereof

Info

Publication number: CN108922709B
Application number: CN201810766797.4A
Authority: CN
Inventors: 朱明刚; 宋利伟; 刘涛; 王欣; 张乐乐; 王誉; 石晓宁; 李卫
Original assignee: Central Iron and Steel Research Institute
Current assignee: Central Iron and Steel Research Institute
Priority date: 2018-07-13
Filing date: 2018-07-13
Publication date: 2021-01-01
Anticipated expiration: 2038-07-13
Also published as: CN108922709A

Abstract

The invention relates to a permanent magnet material with demagnetization-resistant functional gradient and a preparation method thereofA dysprosium or terbium coating layer formed by taking heavy rare earth metal dysprosium or terbium as a diffusion source is arranged on the surface of the bulk magnet; the permanent magnetic material is prepared by coating with a diffusion source and heat treating under vacuum, and in the final product, the anisotropic field H of the material is from the surface of the magnet contacting with the diffusion source to the inside of the magnet_AThe permanent magnet material with gradient distribution and demagnetization resistance is formed by gradient distribution from high to low. The method can improve the coercive force of the cerium (cerium-rich) magnet to a great extent by a dysprosium or terbium infiltration method, improve the demagnetization resistance of the material, greatly reduce the use amount of heavy rare earth, save the cost and promote the balanced utilization of rare earth resources.

Description

Demagnetization-resistant functionally-graded permanent magnet material and preparation method thereof

Technical Field

The invention relates to the technical field of information and magnetic functional materials, in particular to an anti-demagnetization functional gradient permanent magnetic material and a preparation method thereof.

Background

Sintered nd-fe-b magnets have been widely used since 1983 due to their excellent comprehensive magnetic properties. At present, the rare earth raw materials for preparing the neodymium-iron-boron rare earth permanent magnet material mainly comprise neodymium, praseodymium, dysprosium, terbium and the like. With the increasing use amount of neodymium-iron-boron rare earth permanent magnet materials, rare earth metals such as neodymium, praseodymium, dysprosium, terbium and the like become scarce resources, and rare earth metals capable of replacing the scarce resources are urgently needed to be found.

In natural rare earth resources, besides Nd, abundant and cheap metals Ce and La are also available, the total abundance of Ce and La is 3 times of that of Nd and Pr, and the price is less than one tenth. In recent years, more and more researchers have started to research the high-abundance and low-cost Ce metal. The Ce-containing magnet with excellent performance is prepared by adopting a double main phase method disclosed in the Chinese invention patent (CN102800454A), and the production cost of the magnet is greatly reduced while the good magnetic performance is kept.

Although cerium metal, which is abundant and low-cost, is somewhat widely used, it is Ce-rich₂Fe₁₄Anisotropy field H of B_AThe sum magnetic moment Js is far less than Nd₂Fe₁₄And B, the coercive force of the cerium-containing magnet is low, and the cerium-containing magnet prepared by the traditional preparation method cannot meet the performance requirements of users. This also limits the application field of the cerium-containing magnet, and how to improve the coercivity of the cerium-containing magnet becomes a hot spot of current research.

In recent years, new processes have been used to improve the coercivity of sintered nd-fe-b magnets. The Micunyuan et al, shin-Yuan, 2005 developed a dip coating process for grain boundary thermal diffusion of heavy rare earths. The compound of heavy rare earth Dy and Tb is attached to the surface of sintered magnet by dipping in solution, and then thermal diffusion and ageing treatment are carried out. They found that Dy diffusion increases the coercivity by 3.14-5.02 kOe, and Tb diffusion increases the coercivity by 8.16-10.0 kOe. In Chinese invention patent (CN101641750A), Japanese patent (JP-A2004-377379 and JP-A2005-0842131), disclosed is a method for obtaining a heavy rare earth element coating on the surface of a magnet by impregnating or coating a slurry or suspension of metal Dy or Tb powder or oxide, fluoride or other compound powder thereof. The method disclosed in the Chinese invention patent (CN104134528A) adopts a spraying technology to obtain a coating on the surface of a sintered NdFeB sheet magnet, and then adopts a grain boundary diffusion technology to improve the performance of the sintered NdFeB sheet magnet. The invention application (CN104164646A, CN104576016A) in China discloses that dysprosium or terbium is enabled to enter main phase crystal grains of an NdFeB magnet through a surface dysprosium or terbium permeation technology so as to improve the coercive force of the NdFeB magnet.

The above patent or patent application relates to the method of dysprosium and terbium infiltration in which the main hard magnetic phase of neodymium-iron-boron is Re₂Fe₁₄B and Re are one or more of Pr, Nd, Dy, Tb, Ho and Gd, cerium-rich magnets are not involved, and the preparation of an anisotropic field H by a grain boundary diffusion technology of the cerium-rich magnets is not involved in other prior arts_AThe functional permanent magnetic material with gradient distribution is reported.

Disclosure of Invention

The invention aims to provide a demagnetization-resistant functionally-graded permanent magnet material based on a cerium (cerium-rich) magnet matrix and a preparation method thereof.

The purpose of the invention is realized by the following technical scheme:

a permanent magnetic material with demagnetization resistance and functional gradient takes cerium or cerium-rich permanent magnetic alloy as a matrix magnet, and a dysprosium or terbium coating layer formed by taking heavy rare earth metal dysprosium or terbium as a diffusion source is arranged on the surface of the matrix magnet; the diffusion source is a compound of RHTM, RH is dysprosium or terbium which is a heavy rare earth element, and TM is one of oxygen, fluorine and hydrogen;

the permanent magnetic material is prepared by coating with a diffusion source and heat treating under vacuum, and in the final product, the anisotropic field H of the material is from the surface of the magnet contacting with the diffusion source to the inside of the magnet_AThe permanent magnet material with gradient distribution and demagnetization resistance is formed by gradient distribution from high to low.

The anisotropy field H of the permanent magnet material_AThe gradient value theta is 32-52 degrees, and the gradient value theta is H by adopting a least square method_AAnd calculating and fitting the gradient curve to obtain an approximate included angle between the gradient curve and a horizontal line of a horizontal axis of the diffusion depth.

The permanent magnet material is a single-main-phase or double-main-phase cerium or cerium-rich matrix magnet, and heavy rare earth metal dysprosium or terbium is enriched in a main-phase grain epitaxial layer and a grain boundary thereof as follows: on the epitaxial layer of the grains of the magnetic main phase, the anisotropy field H of the material from outside to inside_AThe materials are distributed in a gradient manner from high to low; there is a diffusion source concentration gradient in the grain boundaries of the grains of the magnetic main phase.

In a single-or dual-main-phase cerium or cerium-rich matrix magnet, the thickness of the epitaxial layer of the main-phase grains with high cerium content is greater than that of the main-phase grains with low cerium content.

The matrix magnet is a single-main-phase or double-main-phase cerium (cerium-rich) magnet [ (Ce, Re) -Fe-B ], and Re is one or more of rare earth elements La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

Dysprosium or terbium metal is coated by the diffusion source coating method: and (3) dipping, evaporation, vacuum sputtering, nano powder coating and other methods, so that the diffusion source is attached to the surface of the cerium or cerium-rich magnet.

The permanent magnetic material has the following temperature characteristics: in the temperature range of 300K-420K, the temperature coefficient alpha of remanence is-0.105%/K-0.129%/K, and the temperature coefficient beta of coercive force is-0.515%/K-0.574%/K.

A method for preparing a permanent magnet material with anti-demagnetization functional gradient comprises the steps of coating dysprosium metal or terbium metal as a diffusion source on the surface of a cerium magnet or a cerium-rich magnet, wherein the diffusion source is a compound of RHTM, RH is dysprosium or terbium which is a heavy rare earth element, and TM is one of oxygen, fluorine and hydrogen; then heat treatment is carried out under the vacuum condition, so that heavy rare earth dysprosium or terbium element enters the surface of the cerium or cerium-rich magnet and the crystal boundary thereof, and the composition and the structure of the material are continuously changed from the surface to the inside, so that the anisotropic field H of the material is from the surface of the magnet which is in contact with a diffusion source to the inside of the magnet_AThe permanent magnet material with gradient distribution and demagnetization resistance is formed by gradient distribution from high to low.

The diffusion source coating method comprises the methods of dipping, evaporation, vacuum sputtering, nano powder coating and the like, wherein a diffusion source is heavy rare earth element dysprosium or terbium, oxides and fluorides thereof, and alcohol solution which is favorable for diffusion is selected as a diffusion medium.

When the diffusion source coating is dip coating, the preparation method comprises the following steps:

(1) cutting a single-main-phase or double-main-phase cerium or cerium-rich sintered magnet to obtain a magnet blank in the shape of a final product, and grinding, polishing, cleaning and airing the surface of the magnet blank for later use;

(2) carrying out hydrogen crushing on metal dysprosium or terbium to obtain coarse powder with the particle size of 100-300 mu m;

(3) placing the coarse powder obtained in the step (2) in a planetary ball milling tank for ball milling to prepare powder, and obtaining fine powder with the powder particle size of 2-5 microns;

(4) mixing the fine powder obtained in the step (3) with absolute ethyl alcohol according to a ratio of 2-5 g: uniformly mixing 10-30 ml of the raw materials to obtain a dipping mixed solution;

(5) under the protection of inert gas, putting the blank magnet into the dipping mixed liquid for 10-30 s, then taking out and standing for 15-30 min, so that dysprosium or terbium forms a coating layer on the surface of the cerium or cerium-rich sintered blank magnet;

(6) carrying out vacuum diffusion heat treatment on the immersed blank magnet for 2-10 hours at 800-950 ℃, and then carrying out vacuum aging treatment for 2-10 hours at 460-520 ℃;

(7) and cooling the magnet after heat treatment to below 50 ℃ by water cooling or air cooling to obtain the permanent magnet material with gradient distribution and demagnetization resistance.

In the step (3), the warp is cut into a diameter

Is 10~20mm, and the height is 5~10 mm's cylinder, or the length of side is 10~30 mm's cube or cuboid, to surface polishing, polishing removal impurity and oil stain, the supersound is dried for use in 5~10 minutes in the deionized water.

When the diffusion source coating is evaporation, the steps (2) and (3) are as follows:

(2) polishing and polishing the surface of dysprosium or terbium metal with the purity of 99.9% after removing impurities of an oxide layer to obtain a diffusion source for evaporation;

(3) vacuum-sealing the single-main-phase or double-main-phase cerium or cerium-rich sintered magnet obtained in the step (1) and the dysprosium or terbium diffusion source obtained in the step (2) together into a quartz tube, wherein the vacuum degree is 10^-2Pa. Compared with the prior art, the invention has the beneficial effects that:

(1) from the angle of low coercive force of the cerium-rich magnet, the dysprosium or terbium infiltration technology is adopted, so that the dysprosium or terbium enters a main phase and a crystal boundary of the cerium-rich magnet, the coercive force of the cerium-rich magnet is improved, and the demagnetization resistance of the cerium-rich magnet is further improved.

(2) Compared with Nd-Fe-B magnet, the two substrates are different, the cerium (rich-cerium) magnet is a composite magnet formed by two permanent magnet phases with Nd-Fe-B as a first main phase and Ce-Fe-B as a second main phase, the two permanent magnet phases both have a 2:14:1 structure, and only one permanent magnet in the Nd-Fe-B magnet is usedThere is a homogeneous 2:14:1 major phase, which in turn causes differences in the microstructure of the matrix. In the process of dysprosium or terbium infiltration of the traditional neodymium iron boron magnet, uniform high H is formed around the main phase crystal grains_AIn the dysprosium or terbium cementation process of the cerium (cerium-rich) magnet, the epitaxial layer of the main phase crystal grain obviously presents H in the dysprosium or terbium cementation process of the cerium (cerium-rich) magnet due to the fact that the radius of a cerium atom is larger than that of a neodymium atom and the space occupation of the cerium atom is different to cause the difference of element replacement reaction_AThe functional gradient permanent magnetic material with a special structure is formed.

(3) Two types of main phase crystal grains with high cerium content and low cerium content exist in a double-main phase cerium (cerium-rich) magnet, and the diffusion depths of heavy rare earth elements are different for the two main phase crystal grains with the same structure and different quality. In a dual-main-phase magnet, the epitaxial layers of two different main phases have different thicknesses, the anisotropy field H_AAlso, the values of (A) and (B) are different and are distributed in a gradient manner from the surface of the main phase grains to the inner direction. Similarly, two homogeneous and inhomogeneous main phase grains appear in single main phase cerium (rich cerium) magnet due to element segregation, and further, in the diffusion process, the anisotropy field H of the main phase grain epitaxial layer_AThe main phase crystal grain surface is distributed in a gradient manner towards the inner direction.

Compared with neodymium iron boron magnet, in the diffusion process, because two types of main phase crystal grains with high cerium content and low cerium content exist in the cerium (cerium-rich) magnet, the diffusion depth of heavy rare earth elements is different for the two main phase crystal grains with isomorphism and heterogeneity. In the diffusion process, the heavy rare earth element and the main phase crystal grains with high cerium content are easy to generate replacement reaction, the diffusion depth is larger, and the diffusion depth of the main phase crystal grains with low cerium content is smaller. And the diffusion depth of the main phase crystal grains is uniform in the diffusion process of the neodymium iron boron magnet.

In the final product, the anisotropy field H of the material goes from the surface of the cerium (cerium-rich) magnet in contact with the diffusion source to the inside of the magnet_AThe gradient distribution is formed from high to low (as shown in fig. 2a and 2 b), but the gradient distribution does not exist after the neodymium iron boron magnet is diffused.

(4) For cerium (cerium-rich) magnet, excellent magnetic properties are ensuredIn addition, the cost can be greatly reduced. The invention further improves the coercive force of the cerium (cerium-rich) magnet by dysprosium or terbium infiltration technology, reduces the usage amount of the heavy rare earth terbium and promotes the balanced utilization of rare earth resources. In addition, during dysprosium or terbium infiltration of the traditional neodymium-iron-boron magnet, uniform high H is formed around the main phase crystal grains_AEpitaxial layer, and the anisotropic field H can be prepared by the technique of the present invention_AThe functional permanent magnetic material with gradient distribution improves the thermal stability of the cerium (cerium-rich) magnet to a certain extent, and has positive guiding significance for widening the application range of the cerium (cerium-rich) magnet.

Drawings

FIG. 1a shows the anisotropy field H of a cerium (cerium-rich) magnet according to the invention from the boundary in contact with the diffusion source to the inside of the magnet_AThe variation of the value (average value) with the diffusion depth forms a gradient distribution diagram;

FIG. 1b is a schematic diagram of an approximate angle θ between the gradient curve and the horizontal axis of the diffusion depth;

FIG. 2a is a schematic diagram of the microstructure of an anti-demagnetization functionally graded permanent magnet material of a bi-main phase cerium (cerium-rich) magnet;

fig. 2b is a schematic diagram of the microstructure of the demagnetization-resistant functionally graded permanent magnet material of a single main phase cerium (cerium-rich) magnet.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

The invention greatly improves the coercive force of the cerium (cerium-rich) magnet through a dysprosium or terbium infiltration process, reduces the usage amount of heavy rare earth and reduces the production cost compared with the neodymium iron boron magnet with the same magnetic performance. Meanwhile, for the entire cerium (cerium-rich) magnet, the anisotropy field H goes from the boundary in contact with the diffusion source to the inside of the magnet_AThe change of the value with the diffusion depth forms a gradient distribution (shown in fig. 1), improves the thermal stability of the cerium (cerium-rich) magnet, and widens the application range of the cerium (cerium-rich) magnet.

FIG. 1a shows the cerium (cerium-rich) magnet anisotropy field H from the boundary in contact with the diffusion source to the inside of the magnet_AThe variation of the values (mean) with diffusion depth forms a gradient profile. See the figure1b, in the invention, the least square method is adopted to H_ACalculating and fitting the gradient curve to obtain an approximate included angle theta between the gradient curve and a horizontal line of a horizontal axis of the diffusion depth, and representing H through the approximate included angle theta_AA gradient value.

FIG. 2 is a schematic diagram showing the microstructure of a functionally gradient permanent magnet material with demagnetization resistance, in which FIG. 2a shows a cerium (cerium-rich) magnet with two main phases, the thickness of the epitaxial layers of the two different main phases being different, and the anisotropy field H_AAlso, the values of (A) and (B) are different and are distributed in a gradient manner from the surface of the main phase grains to the inner direction. Similarly, referring to FIG. 2b, in a single main phase cerium (rich in cerium) magnet, two homogeneous and heterogeneous main phase grains are also present due to element segregation, and thus the anisotropy field H of the main phase grain epilayer is generated during diffusion_AThe main phase crystal grain surface is distributed in a gradient manner towards the inner direction.

Example 1 Single major phase-dysprosium penetration

A demagnetization-resistant functionally graded permanent magnet material and a preparation method thereof comprise the following steps:

(1) processing single main phase cerium (rich cerium) sintered magnet into single main phase cerium (rich cerium) magnet by using wire cutting

The cylinder sample is respectively polished by 1500# and 2000# abrasive paper, the cutting lines and impurities on the surface are removed, and then the cylinder is ultrasonically cleaned in deionized water and dried for later use.

(2) Polishing the surface of the metal dysprosium with the purity of 99.9% to remove impurities in an oxide layer, and then carrying out hydrogen crushing to obtain hydrogen crushed powder with the particle size of 100-300 microns.

(3) And (3) placing the hydrogen broken coarse powder obtained in the step (2) into a planetary ball milling tank for ball milling to prepare powder, and obtaining ball milling fine powder with the powder granularity of 2-5 microns.

(4) Under the protection of inert gas, mixing the ball-milled fine powder obtained in the step (3) with absolute ethyl alcohol according to a ratio of 2-5 g: and uniformly mixing 10-30 ml of the mixture to obtain the dysprosium dipping mixed solution.

(5) And (3) under the protection of inert gas, putting the cerium-rich sintered magnet obtained in the step (1) into the dipping mixed liquid obtained in the step (4) for 10-30 s, taking out and standing for 15-30 min to volatilize ethanol, and forming a dysprosium coating layer on the surface of the cerium-rich sintered magnet.

(6) And (3) carrying out vacuum diffusion heat treatment on the coated cerium (cerium-rich) sintered magnet obtained in the step (5) at 850-950 ℃ for 2-10 hours, and then carrying out vacuum aging treatment at 460-520 ℃ for 2-10 hours.

(7) Obtaining dysprosium-infiltrated cerium (cerium-rich) magnet by water cooling or air cooling to below 50 ℃.

And (3) carrying out magnetic property test on the dysprosium-infiltrated single-main-phase cerium (cerium-rich) magnet obtained in the step (7) by using NIM-2000HF permanent magnet material standard measuring equipment, wherein the result is shown in Table 1.

TABLE 1 EXAMPLE 1 magnetic Properties and H of Single-Main-phase cerium (cerium-rich) magnet before and after dysprosium infiltration_AGradient value theta

Single main phase magnet	B_r/kGs	H_cj/kOe	(BH)_m/MGOe	H_k/H_cj	θ/°
						Before dysprosium penetration	13.14	12.16	40.28	0.91	0
After dysprosium penetration	13.08	16.65	40.12	0.88	32

EXAMPLE 2 Single major phase terbium

(2) And polishing the surface of metal terbium with the purity of 99.9% to remove impurities in an oxide layer, and then carrying out hydrogen crushing to obtain hydrogen crushed powder with the particle size of 100-300 microns.

(4) Under the protection of inert gas, mixing the ball-milled fine powder obtained in the step (3) with absolute ethyl alcohol according to a ratio of 2-5 g: and (3) uniformly mixing 10-30 ml of the mixture to obtain a terbium impregnation mixed solution.

(5) And (3) under the protection of inert gas, putting the cerium-rich sintered magnet obtained in the step (1) into the dipping mixed liquid obtained in the step (4) for 10-30 s, taking out and standing for 15-30 min to volatilize ethanol, and forming a terbium coating layer on the surface of the cerium-rich sintered magnet.

(7) The cerium (rich in cerium) magnet infiltrated with terbium is obtained by cooling with water or air to below 50 ℃.

And (3) performing magnetic property test on the terbium-infiltrated single-main-phase cerium (cerium-rich) magnet obtained in the step (7) by using NIM-2000HF permanent magnet material standard measuring equipment, wherein the result is shown in Table 2.

TABLE 2 EXAMPLE 2 magnetic Properties and H of Single-Main-phase cerium (cerium-rich) magnet before and after Terbium impregnation_AGradient value theta

Single main phase magnet	B_r/kGs	H_cj/kOe	(BH)_m/MGOe	H_k/H_cj	θ/°
						Before terbium infiltration	13.18	12.21	40.37	0.93	0
After terbium infiltration	13.02	17.84	40.06	0.89	38

EXAMPLE 3 double major phase terbium

(1) processing a dual-main-phase cerium (rich cerium) sintered magnet into a magnet by wire cutting

And (3) performing magnetic property test on the terbium-infiltrated double-main-phase cerium (cerium-rich) magnet obtained in the step (7) by using NIM-2000HF permanent magnet material standard measuring equipment, wherein the results are shown in Table 3.

TABLE 3 EXAMPLE 3 magnetic Properties and H of two-main-phase cerium (cerium-rich) magnet before and after Terbium impregnation_AGradient value theta

Double-main-phase magnet	B_r/kGs	H_cj/kOe	(BH)_m/MGOe	H_k/H_cj	θ/°
						Before terbium infiltration	13.25	12.53	40.65	0.95	0
After terbium infiltration	13.12	20.17	40.39	0.91	52

Example 4 two major phases-vapor deposition of Terbium

(2) And (3) grinding and polishing the surface of metal terbium with the purity of 99.9% to remove impurities of an oxide layer so as to obtain a terbium diffusion source for evaporation.

(3) The double-main-phase cerium (cerium-rich) sintered magnet obtained in the step (1) and the terbium diffusion source obtained in the step (2) are sealed and placed in a quartz tube in vacuum, and the vacuum degree is 10^-2Pa。

(4) And (3) carrying out diffusion heat treatment on the vacuum sealed cerium (cerium-rich) sintered magnet obtained in the step (3) at 850-950 ℃ for 2-10 hours, and then carrying out aging treatment at 460-520 ℃ for 2-10 hours.

(5) The cerium (cerium-rich) magnet evaporated with terbium is obtained by cooling the magnet to 50 ℃ or below with water or air.

And (3) performing magnetic performance test on the terbium-evaporated bi-main-phase cerium (cerium-rich) magnet obtained in the step (7) by using NIM-2000HF permanent magnet material standard measuring equipment, wherein the results are shown in Table 4.

TABLE 4 EXAMPLE 4 magnetic Properties and H of two-main-phase cerium (cerium-rich) magnet before and after evaporating Terbium_AGradient value theta

Double-main-phase magnet	B_r/kGs	H_cj/kOe	(BH)_m/MGOe	H_k/H_cj	θ/°
						Before evaporating terbium	13.28	12.48	40.58	0.93	0
After terbium evaporation	13.06	19.27	40.15	0.89	47

The above description is only for the purpose of illustrating a few embodiments of the present invention and is not to be construed as limiting the invention in any way, and other variations and modifications will occur to those skilled in the art and are intended to be included within the scope of the present invention.

Claims

1. A permanent magnetic material with demagnetization resistance and functional gradient is characterized in that the permanent magnetic material takes cerium or cerium-rich permanent magnetic alloy as a matrix magnet, the cerium or cerium-rich permanent magnetic alloy is a composite magnet taking Nd-Fe-B and Ce-Fe-B as main phases, and a dysprosium or terbium coating layer formed by taking heavy rare earth metal dysprosium or terbium as a diffusion source is arranged on the surface of the matrix magnet; the diffusion source is a compound of RHTM, RH is dysprosium or terbium which is a heavy rare earth element, and TM is one of oxygen, fluorine and hydrogen;

the permanent magnet material is prepared by diffusion source coating and heat treatment under vacuum, and in the final product, the permanent magnet material is connected with the diffusion sourceAnisotropy field H of material from the surface of the magnet to the inside of the magnet_AThe permanent magnet material with gradient distribution and demagnetization resistance is formed by gradient distribution from high to low.

2. The demagnetization-resistant functionally graded permanent magnet material of claim 1, wherein the permanent magnet material has an anisotropy field H_AThe gradient value theta is 32-52 degrees, and the gradient value theta is H by adopting a least square method_AAnd calculating and fitting the gradient curve to obtain an approximate included angle between the gradient curve and a horizontal line of a horizontal axis of the diffusion depth.

3. The demagnetization-resistant functionally graded permanent magnet material of claim 1, wherein the permanent magnet material is a single-phase or double-phase cerium or cerium-rich matrix magnet, and the heavy rare earth metal dysprosium or terbium is enriched in the main phase grain epitaxial layer and the grain boundary thereof as follows: on the epitaxial layer of the grains of the magnetic main phase, the anisotropy field H of the material from outside to inside_AThe materials are distributed in a gradient manner from high to low; there is a diffusion source concentration gradient in the grain boundaries of the grains of the magnetic main phase.

4. The demagnetization-resistant functionally graded permanent magnet material of claim 3, wherein in the single or dual main phase cerium or cerium-rich bulk magnet, the thickness of the epitaxial layer of the main phase grains with high cerium content is larger than that of the main phase grains with low cerium content.

5. The demagnetization-resistant functionally graded permanent magnet material of claim 1, wherein the base magnet is a single-or dual-phase cerium magnet [ (Ce, Re) -Fe-B ] or a single-or dual-phase cerium-rich magnet [ (Ce, Re) -Fe-B ], Re being one or more of the rare earth elements La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

6. The demagnetization-resistant functionally graded permanent magnetic material of claim 1 wherein the metal dysprosium or terbium is coated by a diffusion source method comprising: dipping, evaporation, vacuum sputtering and nano powder coating methods are adopted, so that the diffusion source is attached to the surface of the cerium or cerium-rich magnet.

7. The demagnetization-resistant functionally graded permanent magnet material of claim 1, wherein the permanent magnet material has the following temperature characteristics: temperature coefficient of remanence in 300-420K temperature rangeαis-0.105%/K to-0.129%/K, coercive force temperature coefficientβThe ratio is-0.515%/K to-0.574%/K.

8. The method for preparing a permanent magnet material with demagnetization resistance function gradient according to claim 1, wherein metal dysprosium or terbium is used as a diffusion source to coat the surface of the cerium magnet or the cerium-rich magnet, the diffusion source comprises RHTM compounds, RH is heavy rare earth element dysprosium or terbium, and TM is one of oxygen, fluorine and hydrogen; then heat treatment is carried out under the vacuum condition, so that heavy rare earth dysprosium or terbium element enters the surface of the cerium or cerium-rich magnet and the crystal boundary thereof, and the composition and the structure of the material are continuously changed from the surface to the inside, so that the anisotropic field H of the material is from the surface of the magnet which is in contact with a diffusion source to the inside of the magnet_AThe permanent magnet material with gradient distribution and demagnetization resistance is formed by gradient distribution from high to low.

9. The preparation method of claim 8, wherein the diffusion source coating method comprises dipping, evaporation, vacuum sputtering and nano-powder coating methods, the diffusion source comprises RHTM compound, RH is dysprosium or terbium which is a heavy rare earth element, TM is one of oxygen, fluorine and hydrogen, and alcohol solution which is favorable for diffusion is selected as the diffusion medium.

10. The method of claim 9, wherein when the diffusion source coating method is dip coating, the method comprises the steps of:

(6) carrying out vacuum diffusion heat treatment on the immersed blank magnet for 2-10 hours at the temperature of 800-950 ℃, and then carrying out vacuum aging treatment for 2-10 hours at the temperature of 460-520 ℃;

(7) and (3) cooling the magnet after heat treatment to below 50 ℃ by water or air to obtain the permanent magnet material with gradient distribution and demagnetization resistance.

11. The preparation method according to claim 10, wherein in the step (1), the warps are cut into cylinders with the diameter phi of 10-20 mm and the height of 5-10 mm, or cubes or cuboids with the side length of 10-30 mm, the surfaces of the cylinders are ground and polished to remove impurities and oil stains, and the cylinders are ultrasonically dried in deionized water for 5-10 minutes for later use.