Study On The Intrinsic Magnetism And Coercivity Mechanism Of High Abundant Rare Earth Permanent Magnetic Materials

High abundance rare earth permanent magnetic material is a kind of an irreplaceable important functional material and is widely used in various aspects of daily life,attracting people's attention.The intrinsic magnetic properties of the material and its relationship with temperature have important implications for the design of the magnet composition,the optimization of process conditions,the applicable temperature range,and the material cost-effectiveness.Full understanding of the coercivity mechanism of high-abundance dual-phase sintered magnets has very important guiding significance for the production and performance regulation of dual-phase sintered magnets and the development of new materials.The use of the dual main phase method to directly use the mixed rare earth to replace part of the Nd to prepare the permanent magnetic material not only can fully utilize various rare earth resources,but also can reduce the environmental pollution caused by rare earth separation and save the cost of raw materials.In this paper,the intrinsic magnetic properties of MM₁₃Fe₈₁B₆(composite La_28.2Ce_52.0Pr_5.1Nd_14.7 alloy with mixed rare earth MM)and the permanent magnetic properties of the double-phase MM₁₄Fe_79.9B_6.1/Nd_13.5Fe_80.5B₆ sintered magnet are studied.The coercivity mechanism and the relationship between the magnetization process and magnetic domains in different initial states of sintered magnets are analyzed.The main results obtained are as follows:The MM₁₃Fe₈₁B₆ alloy was prepared by arc melting and the lattice constant of MM₂Fe₁₄B was calculated by GSAS refinement to obtain a=b=0.8780 nm,c=1.2185 nm,which is slightly lower than that of Nd₂Fe₁₄B.The saturation magnetization of MM₂Fe₁₄B crystal is 27.36?_B/f.u.at 300 K fitted with the saturation law,and its trend with temperature is similar to that of Nd₂Fe₁₄B.The relationship between the saturation magnetization of MM₂Fe₁₄B and the temperature was fitted using a molecular field model.The fitting value and experimental results had the same trend.A polycrystalline orientation sample with a good c-axis arrangement was prepared using the powder orientation method.The anisotropy field of MM₂Fe₁₄B crystal at the temperature of 300 K was calculated by the energy relationship in the direction of magnetization and the hard axis of the magnet.The anisotropy field?₀H_a=4.2 T,the anisotropy constant K₁=1.39×10⁶ J/m3,K₂=4.2×105 J/m³.The magnetocrystalline anisotropy constants of MM₂Fe₁₄B crystals at different temperature were very close to the experimental values using the single-anode anisotropy theory,and the change relationship was similar to that of Nd₂Fe₁₄B.With the decrease of temperature,the spin reorientation phenomenon occurs at 74 K in the MM₂Fe₁₄B magnet,and the spin reorientation angle reaches 18°at 10 K.The Curie temperature of the MM₂Fe₁₄B magnet is 488 K,which means that the magnet can be used at room temperature.A sintered magnet with the ratio of MM₁₄Fe_79.9B_6.1/Nd_13.5Fe_80.5B₆ in the order of0:100,20:80 and 30:70 was prepared by a double main phase method.The magnets mainly contain a 2:14:1 main phase,contain only a small amount of?-Fe phase,and the magnets with different compositions have almost the same degree of crystal orientation,with a standard deviation of about 14°.The Curie temperature of Nd₂Fe₁₄B is T_C=585.2 K.When the mixed rare earth MM accounts for 20.2 at.%and30.3 at.%of the total rare earth,the magnet has three different magnetic phase transition temperature,T_C1,T_C2,and T_C3,followed by 509.4 K,565 K,573.2 K,and508.8 K,555.2 K,568.8 K respectively.As the content of mischmetal increases,the content of the grain boundary phase in the magnet increases,the uneven distribution thereof increases,the permanent magnet performance of the magnet gradually decreases,and the exchange coupling effect inside the magnet weakens,and the magnetization reversal process becomes more inconsistent.As the temperature rises,the permanent magnet performance of the magnet becomes weaker,the squareness of the demagnetization curve deteriorates,and the magnetization process and the interaction between crystal grains of the internal magnetite significantly change.The higher the temperature,the more independent the magnetization reversal process of the different grains in the magnet becomes,and the exchange coupling between crystal grains becomes weaker and the magnetization reversal process becomes more inconsistent.The double-phase magnets have different coercivity mechanisms at different temperatures.The magnets approach nucleation at 200 K,while the domain wall pinning dominates at 380 K.At 300 K the magnetization process is relatively complex.The coercivity mechanism and the magnetization reversal process cannot be described by a single coercivity mechanism.The 300 K angular FORC and SORC distribution curves confirm that the magnet does have two types of magnetization reversal mechanisms.The magneto-optical Kerr microscope was used to observe the magnetic domain states of the sintered magnets of different compositions in different initial states.It was found that when the magnets were thermally demagnetized,the internal grains of the magnets were in a multi-domain state,and the grains in the AC demagnetization state were almost completely monodomains.The recovery curve of the initial magnetization process of the thermal demagnetization reflects the specific conditions of the movement and disappearance of the magnetic domain walls within the grains,and the demagnetization recovery curve reflects the magnetization reversal of the crystal grains and the interaction between the crystal grains.The recovery curve of the initial magnetization of the AC demagnetization and the demagnetization recovery curve indicate the same magnetic properties,both of which reflect the magnetization reversal of the crystal grains inside the magnet and the interaction between the crystal grains,and the recovery curve of the demagnetization process has nothing to do with the initial state of the magnet.There is obvious asymmetry in the minor loop of thermal demagnetization,and the change process of minor loops under different magnetic fields is more complicated.This is due to the mixed overlapping of crystal grains in the magnet from multi-domain to single domain and single domain reversal magnetization.The minor loop of AC demagnetization has good symmetry,reflecting the magnetization reversal of the grains inside the magnet and the interaction between the grains.The recovery curve of the thermal demagnetization state and the minor loop process are equivalent with each other,reflecting the same magnetic properties.