Study On Preparation And Magnetic Properties Of Nd-Ce-Fe-B Permanent Magnet Films

Permanent magnets are widely used in various industries.Due to the excellent properties,Nd-Fe-B based rare earth permanent magnets are widely used in wind power generation,energy-saving household appliances,new energy vehicles and medical equipment.The production of high-performance Nd-Fe-B magnets requires a large number of Nd,Pr,Tb and Dy,but the high-abundance rare earth Ce associated with them can only be developed as a by-product and has been backlogged for a long time.How to use Ce to obtain high-performance permanent magnets is a research hotspot of researchers.Previous studies have found that Re-Fe-B magnets with high Ce content have poor magnetic properties,so this paper aims to improve the coercivity of Nd-Ce-Fe-B magnets with high Ce content.Firstly,the optimal experimental scheme for preparing Nd-Ce-Fe-B thin films was found by ultra-high vacuum magnetron sputtering.Besides,Nd-Ce-Fe-B thin films with high coercivity were obtained by grain boundary diffusion technology.To solve the‘shoulder problem'in the hysteresis loop of Nd-Ce-Fe-B magnetic thin films,we found out the cause of the problem by changing the preparation conditions and put forward the solution.The main contents and conclusions of this paper are as follows:?1?In this paper,Nd-Ce-Fe-B thin films were prepared by magnetron sputtering,and the sputtering process was optimized.It was found that the highest coercivity permanent magnet thin films could be obtained by using Ta/[Nd-Ce-Fe-B/Cu/Ce/Cu]₂/Ta design.After adjusting the thickness of Cu and Ce,it was found that when the thickness of Ce was fixed at 20 nm,the coercivity of the films first increased and then decreased with the increase of the thickness of Cu.When the thickness of Cu was 1 nm,the highest coercivity was 24.8 kOe,and Ce accounted for 67.3 at.%of the total rare earth content.Then,when a single layer of Ta/[Nd-Ce-Fe-B/Cu/Ce/Cu]/Ta is used and the thickness of Cu is fixed at 1.5 nm,the coercivity of the thin films increased first and then decreased with the increase of the thickness of Ce.When the thickness of Ce was20 nm,the coercivity was 23 kOe,and Ce accounted for 66.4 at.%of the total rare earth content.The coercivity of these two designs is increased by more than 100%than that of the films prepared without grain boundary diffusion technology.Subsequently,the thin film samples were analyzed by micromagnetic simulation combined with TEM and MFM characterization photos.The results show that the main phase grain boundary can be enriched and the grains are separated by using Ce-Cu eutectic phase with low melting point to diffuse the grain boundary,thus achieving decoupling and improving the coercivity.?2?Ta/Nd-Ce-Fe-B/Ta films with different deposition temperatures and thickness of the main phase have been prepared.The relationship between hysteresis loop and phase composition is also studied.It is found that CeFe₂ phase appears more or less in Ce magnets.When the thickness of the main phase is reduced and the deposition temperature is fixed at 600?,the content of CeFe₂ phase is relatively low.When the content of CeFe₂ phase is high,the coercivity will increase but the square degree will be poor,and the formation of alpha-Fe phase will occur at the same time.This is due to the decomposition of the main phase into CeFe₂ phase and?-Fe phase during growth and annealing.Among them,CeFe₂ phase can lubricate grain boundaries and improve the microstructure,which results in the increase of the coercivity of the film;while alpha-Fe phase will lead to the‘shoulder'of the hysteresis loop,the reduction of the remanence and deterioration of the square degree.