Advance in the chemical synthesis and magnetic properties of nanostructured rare-earth-based permanent magnets

Rare-earth-based permanent magnets are one of the most important magnets in both scientific and industrial fields. With the development of technology, nanostructured rarearth-based permanent magnets with high energy products are highly required. In this article, we will review the progress in chemical synthetic strategies of nanostructured rare-earth-based permanent magnets.

Rare earth permanent magnets Sm_2(Co, Fe, Cu, Zr)_17 for high temperature applications

Sintered Sm（Coba1FexCu0.1Zr0.03）7.5 （x=0.09-0.21） permanent magnets with higher Fe content were found to have higher remanence Br and maximum energy product （BH）max at room temperature. Br and （BH）max reached maximum of 0.96 T and 176.7 kJ/m^3, respectively at room temperature when the Fe content x reached 0.21. However, the intrinsic coercivity Hci at room temperature increased gradually when the Fe content x increased from 0.09 to 0.15, but when x further increased to 0.21, Hcidecreased. Hci attained its peak value of 2276.6 kA/m with Fe content x=0.15 at room temperature. For magnets with x=0.15, Br, （BH）max and Hc1 reached 0.67 T, 81.2 kJ/m^3 and 509.4 kA/m at 500 ℃, respectively, showing good high temperature stability, which could be used in high temperature applications.

Development of Strip Casting Technology in Rare Earth Permanent Magnet Alloys and Hydrogen Storage Alloys in China

The SC technique is now being applied widely in material preparation, especially in rare earth functional materials in virtue of its advanced process and high performance product. The applications of SC technique in rare earth permanent magnet alloys and hydrogen storage alloys were analyzed integrative, on the basis of summary of SC technique development in this paper. The paper mainly includes development history of SC technology, effect of SC technology on alloy microstructure, application of SC technology in RE storage hydrogen alloy and sintered Nd-Fe-B alloy, development of SC equipment and SC product industry. At the same time, the paper points out the existing problem of SC products.

The Stability of Rare Earth-Iron-Nitrides Sm_2(Fe,M)_(17)N_y,Permanent Magnets

The effects of the partial substitution of element M(M=Cr,V,Mn,x=0.05;Zr,Ga,x=0.017; Si,x=0.15;Co,x=0.10)for Fe in samarium-iron-nitride Sm_2(Fe_(1-x)M_x)_(17)N_y compounds on their stabilities and Curie temperatures have been studied.It is found that Co,Ga can raise the Curie temperature of the compounds.The initial decomposition temperatures cannot be raised significantly by all the studied elements except Co.The result contradicts the formation enthalpy consideration.The final decomposition tempera- tures can be raised by all of the substitution elements.The effects of atmospheres on their decomposition be- havior were also studied.The results show that oxidation is the major reason for magnetic deterioration of the powder heated in air.Compared with nitrogen atmosphere,argon or vacuum helps to delay the decompo- sition of the compounds.

Permanent Rare-Earth Magnets—The Need to Protect Them against Corrosion

The RE-Fe-B permanent magnets have a complex microstructure and they are susceptible to corrosion process. In this paper, the commercial nickel coatings adhesion was investigated. The microstructure of the RE-Fe-B without coating was analyzed by scanning electronic microscopy and electrochemical techniques. The interface magnet/coating was studied by scanning electron microscopy and the nickel-plated Nd-Fe-B commercial magnets were tested in a salt spray chamber. The ferromagnetic and RE-rich phases were observed. After the anodic polarization curve, a strong intergranular corrosion was observed and the RE-rich phase was preferentially attacked. The interface magnet/Ni coating presented inter-granular corrosion that can affect the nickel coating adherence. This attack had probably occurred during the electrodeposition process. Not all the samples suffered localized corrosion during the salt spray tests and the Ni triple-layer coating presented a few corrosion points. RE-Fe-B alloy magnets need to be protected with appropriate coatings to each environment to which they will be exposed and the protective coating must not be damaged.

China’s export of rare earth permanent magnet products was stable in April 2019

China is a global prcducec and expoCec of rcrc each perma nent mag net products. ExpoC is one of the impoCant salos channels for many large and medium-sized magnetin materinl prcductinn entercrises in China.

An Empirical Study of CAPM’s Applicability to Rare Earth Permanent Magnet Material Stocks

China has the world’s largest reserves of rare earth elements.Rare earth permanent magnet material has always been one of the popular industries in the investment market.CAPM is the basic asset-pricing model in financial economics.There are a number of studies conducted to examine the applicability of CAPM to stock markets in different industries and to investigate the modification method to improve the model’s prediction accuracy.In this study,seven leading enterprises in China’s rare earth permanent magnet material industry listed on the A-share market were selected as the research subjects.Based on CAPM,regression analysis was conducted on the monthly data from March 2016 to February 2022.The results demonstrated that using the β coefficient to explain the risk of China’s rare earth permanent magnet industry is ineffective.The ultimate benefit was less affected by market indexes but mainly by non-systematic risks.CAPM has low applicability to China’s rare earth permanent magnet material industry and requires further improvement.Nevertheless,CAPM still has some guiding significance in making enterprise comparisons and investment decisions.

The use of permanent magnet motor for Tesla electric vehicle stimulates the demand for rare earth Nd

On March 13th,Reuters reported that the long run version of Tesla Model 3 will use permanent magnet motors.One of the materials for this type of motor is rare earth metal neodymium,which will further increase the supply pressure of neodymium.Governments around the world are committed to reducing the harmful emissions produced by fossil fuel cars,pushing up demand for electric vehicles

Rare Earths and Magnetic Refrigeration

Magnetic refrigeration is a revolutionary, efficient, environmentally friendly cooling technology, which is on the threshold of commercialization. The magnetic rare earth materials are utilized as the magnetic refrigerants in most cooling devices, and for many cooling application the Nd2Fe14B permanent magnets are employed as the source of the magnetic field. The status of the near room temperature magnetic cooling was reviewed.

Development of permanent magnetic refrigerator at room temperature

A reciprocating magnetic refrigerator was developed based on the active magnetic regeneration technology. Rare earth metal Gd and intermetallic compound LaFe11.2Co0.7Si1.1 were used as the magnetic operating materials in the machine. The particles of the magnetic operating materials, with diameter of 0.5-2 mm and total mass of 950 g, were mounted in the cooling bed. A magnetic field was assembled using NdFeB rare earth permanent magnets. It had the magnetic field space of Φ 34×200 and the magnetic induction of 1.5 T. The water at pH=10 is used as a heat transfer fluid. When the ambient temperature is 296 K, a temperature span of 18 K was achieved after operation of 45 min at a frequency of 0.178 Hz. The temperature span and the output power increase significantly with the increasing velocity of heat transfer.

Investigation on mechanism of magnetization reversal for nanocrystalline Pr-Fe-B permanent magnets by micromagnetic finite element methods

Magnetization configurations were calculated under various magnetic fields for nanocrystalline Pr-Fe-B permanent magnets by micromagnetic finite element method.According to the configurations during demagnetization process, the mechanism of magnetization reversal was analyzed.For the Pr2Fe14B with 10 nm grains or its composite with 10vol.% α-Fe, the coercivity was determined by nucleation of reversed domain that took place at grain boundaries.However, for Pr2Fe14B with 30 nm grains, coercivity was controlled by pinning of the nucle-ated domain.For Pr2Fe14B/α-Fe with 30vol.% α-Fe, the demagnetization behavior was characterized by continuous reversal of α-Fe moment.

Dependence of Magnetic Properties of Rapidly Quenching (Nd,Pr)_x (FeCoZr)_(94-x)B_6 Bonded Magnets on Rare Earths Content

By using sub-overquenching and annealing method which has a wide processing window, (Nd, Pr), ( Fe-CoZr)(94-x)B-6(x = 12, 10.5, 10, 9) bonded magnets were prepared and the effect of rare earths content on magnetic properties was investigated. Being spun at sub-ove.quenching speed the as-spun ribbons consist of amorphous phases mixed with fine crystallites. After crystallization under optimum annealing conditions and bonded with 3.25% (mass fraction) epoxy, the magnets obtained the optimum magnetic properties. The rare earths content directly determines the magnetic properties. With the reduction of rare earths content, B-r increases but H-ci and (BH)(max) decrease. x = 10 is the critical value for the magnetic proper-ties change. Below this value, Br increases slowly meanwhile H-ci and (BH)(max) decrease strongly because alloy contains extra fractions of soft magnetic phase which are not coupled with the hard magnetic phase.. This experimental result is consistent with the calculated results using the model of volume fraction of soft magnetic phase coupled completely suggested.

Preparation Technology and Performances of Zn-Cr Coating on Sintered NdFeB Permanent Magnet

Zn-Cr coating was prepared on the surface of sintered NdFeB permanent magnet samples and preparation parameters were established. The anticorrosive property of Zn-Cr coating on NdFeB was studied by whole-immersion test in NaCl solution and compared with that of zinc plating and nickel plating on NdFeB. Open-circuit potential and self-corrosion current of NdFeB samples with and without Zn-Cr coating were measured. The micro-morphology and composition of Zn-Cr coming were analyzed through SEM, XPS, EDS and XRD. The effect of Zn-Cr coating on magnetic property of NdFeB magnet was also investigated. It is exposed that Zn-Cr coating is anodic type coating for NdFeB magnet, and provided substrate electrochemical protection, barrier protection and passivation protection. The anticorrosion property of NdFeB magnet is obviously enhanced by Zn-Cr coating while the magnet property of NdFeB magnet changed little.

ThMn12-Type Alloys for Permanent Magnets

Iron-rich compounds with the tetragonal ThMn12-type structure have the potential to meet current demands for rare-earth-lean permanent magnets with high energy density and operating temperatures of 150-200℃.However,while it is normal for magnet technology to lag behind the development of underlying magnetic material,this gap has always been unusually large for ThMn12-type magnets.The gap has widened further in recent years,as excellent combinations of intrinsic magnetic properties have been obtained in compounds synthesized with a smaller amount of structure-stabilizing elements(e.g.,SmFe11V or Sm0.8Zr0.2Fe9.2Co2.3Ti0.5)or with no such elements(i.e.,SmFe9.6Co2.4 thin films).The search for promising compounds continues-with increasing help coming from theoretical calculations.Unfortunately,progress in the development of magnets beyond polymer-bonded interstitially modified powders remains marginal.The introduction of lanthanum(La)was found to stabilize low-meltingtemperature minority phases in Sm(Fe,Ti)12 alloys,thus allowing for liquid-phase sintering for the first time.The high reactivity of La,however,has apparently undermined the development of coercivity(Hc).A controlled crystallization of the initially suppressed ThMn12-type phase makes"bulk"magnetic hardening possible,not only in Sm-Fe-V alloys(in which it has been known since the 1990s),but also is in La-added(Ce,Sm)(Fe,Ti)12 alloys.The properties of the bulk-hardened alloys,however,remain unsatisfactory.Mechanochemically synthesized(Sm,Zr)(Fe,Si)12 and(Sm,Zr)(Fe,Co,Ti)12 powders may become suitable for sintering into powerful fully dense magnets,although not before a higher degree of anisotropy in both alloys and a higher Hc in the latter alloy have been developed.

Anisotropy of rare-earth magnets

Rare-earth intermetallics such as Nd2Fe14B and Sm-Co are widely used as high-performance permanent magnets, because they combine high magnetocrystalline anisotropy with reasonable magnetization and Curie temperature. The anisotropy is a combined effect of spin-orbit coupling and electrostatic crystal-field interactions. The main contribution comes from the rare-earth 4f electrons, which are well-screened from the crystalline environment but exhibit a strong spin-orbit coupling. In this limit, the magnetocrystalline anisotropy has a very transparent physical interpretation, the anisotropy energy essentially being equal to the energy of Hund＇s-rules 4f ion in the crystal field. The corresponding expression for the lowest-order uniaxial anisotropy constant K1 is used to discuss rare-earth substitutions, which have recently attracted renewed interest due to shifts in the rare-earth production and demand. Specific phenomena reviewed in this article are the enhancement of the anisotropy of Sm2Fe17 due to interstitial nitrogen, the use of Sm-Co magnets for high-temperature applications, and the comparison of rare-earth single-ion anisotropy with other single-ion and two-ion mechanisms.

Application of high-temperature permanent magnets Sm(Co, Fe, Cu, Zr)_Z in PPM focusing system

Rare earth permanent magnets Sm（Co, Fe, Cu, Zr）z with outstanding performance and high-temperature thermal stability were fabricated. Optimized by Fe content and process, Sm（Co0.72Fe0.15Cu0.1Zr0.03）7.5 magnet with B1〉0.75 T and Hci〉1300 kA/m at 300 ℃ can be obtained. According to the performance data of Sm（Co0.72Fe0.15Cu0.1Zr0.03）7.5, the magnetic field along central axis Bz in periodic permanent magnet （PPM） focusing system was simulated using electromagnetic field analysis software Maxwell 2D/3D. The Bz exhibited typical cosine curve along central axis, and the peak value of Bz was high enough to meet the demand of PPM focusing system at room temperature even at 200±20 ℃. Additionally, a kind of simple cooling structure for PPM focusing system was designed by setting cooling pipe between polepieces. Simulated results showed that smooth cosine curve of Bz was successfully achieved with good control of the thickness of cooling pipe.

Antioxidation Study of Sm(Co, Cu, Fe, Zr)_z-Sintered Permanent Magnets by Metal Injection Molding

Antioxidation effects on Sm （Co, Cu, Fe, Zr）z-sintered magnets treated by different methods were studied through TGA and DTA. Microstructure of Sm（Co, Cu, Fe, Zr）z-sintered magnets was analyzed through SEM and EDS. The results indicate that the antioxidation effect of the alloy powder treated in silane solution is better than that of the other methods. The alloy powders treated in stearic acid （SA） solution and polymethyl methacrylate （PMMA） solution can prevent powders from oxidation for a short period of time. Silane solution is not suitable for metal injection molding （MIM） because it severely damages the magnetic properties and microstructure of Sm（Co, Cu, Fe, Zr）z-sintered magnets. SA solution can not only prevent powders from oxidizing in MIM, but also does not damage magnetic properties and microstructure of Sm（Co, Cu, Fe, Zr）z magnets. The oxygen content of Sm（Co, Cu, Fe, Zr）z-sintered magnets by MIM is 3300μg·g^-1.

Research and Develop ment of Rare Earth Per manent Magnets in China

The research and development of RE magnets in China were briefly reviewed. The research achievements of RE magnets reach international level. The intermetallic nitrides with ThMn12-type structure of RFe series which possess Chinese proprietary were prepared. The output of RE magnets has ranked second in the world. The production of RE magnets will be steadily expanding with the expiration of NdFeB patent in 2003. Some related data were also presented.

A Study of Two-Phase Nanocrystalline Nd_(8.5)Fe_(75)Co_5Cu_1Zr_3Nb_1B_(6.5)Permanent Magnet

Nanocrystalline Nd 8.5 Fe 75 Co 5Cu 1Zr 3Nb 1B 6.5 ribbons were prepared by melt spun (18 m·s -1 ) and subsequent heat treatment (670 ℃/4 min). Excellent magnetic properties of the bonded magnet were achieved as follows: B r=0.68 T (6 8 kGs), J H c=620.3 kA·m -1 (7.8 kOe), ( BH ) max =74 kJ·m -3 (9 3 MGOe). The results of TEM photomicrographs confirm that the appearance of α Fe phase is earlier than that of Nd 2Fe 14 B phase during crystallization process. The addition of Cu and Zr elements shows to be advantageous to the improvement of an intrinsic coercivity and squareness of hysteresis loop, as well as energy product.