Structure And Magnetic Properties Of Fe-based Hard Magnet Material

Hard magnetic materials,also called permanent magnetic materials,have becoming important functional materials in national defense and technology due to their excellent magnetic properties..Among them,the two Fe-based permanent magnetic materials,such as NdFeB and FePt show the fastest growing.L1₀-ordered FePt alloys are suitable for the ultrahigh density perpendicular magnetic recording medium because of the large uniaxial magnetic anisotropy energy.Sintered NdFeB magnets are widely used in industrial motors and generators due to the high magnetic energy product.In this thesis,we studied the structure and magnetic properties of L1₀-FePt alloy film and NdFeB hard magnet materials,and the main conclusions are as follows:（1）FePt-ZrO₂-C films were fabricated at high temperature by magnetron sputtering-EB combined system,and the intermediate layer was ZrN-Xvol.%ZrO₂ with different doping content of ZrO₂.The crystallographic texture,microstructure and magnetic properties of the films were analysized.With the increase of ZrO₂ content,the c axis of L1₀-FePt films was changed from the in-plane to the out-of-plane,and the order and perpendicular coercivity of films increased first and then decreased.When ZrO₂ was mixed with 30vol.%in the intermediate layer of ZrN,the film showed（001）orientation,and the coercivity reached14.8kOe.It was because the ZrON solid solution and amorphous ZrO₂ particles can be formed simultaneously when 30vol.%ZrO₂ was doped into ZrN layer.Thereafter,the FePt grains were epitaxially on the top of ZrON layer,resulting in a significant enhancement of magnetic properties for thin films.（2）The planetary high-energy ball milling was used to prepare a series of NdFeB powders with different particles sizes,which varied between 0.26μm and 3.50μm.By optimizing of the milling time,rotational speed,the diameter of grinding ball,the power particle size can be arbitrary regulation.The test results show the coercivity and remanent magnetization of NdFeB powders increased with the decreased particle sizes,but the corresponding sintered magnets with small magnet density and cannot meet the requirements of practical application.Such a result is attributed to the NdO_x phase converted from Nd-rich phase with decreasing powder sizes,which caused the decrease in the volume fraction of the Nd-rich phase.So the tranditional process parameters cannot be used to prepare the NdFeB magnets with small sizes.The process parameters should be adjusted to obtain the better magnetic properties for NdFeB.