Magnetic Properties And Microstructures Of Anisotropic Nd-Ce-Fe-B Multilayers Magnetic Thin Films

The miniaturization of devices has become one of the important aspects of people's attention and development,as the advancement of modern science and technology.The rare earth permanent magnetic films,especially Nd Fe B magnetic film,have broad application prospects in magnetic sensor,ultrahigh density magnetic storage device and micro electro mechanical system?MEMS?.The Nd-Ce-Fe-B monolayer and multilayer films were prepared by DC magnetron sputtering technique.By optimizing the microstructure and preparation technology,the magnetic performance gradually improved.The exchange coupling between the hard magnetic layers with various magnetocrystalline anisotropy for Nd-Ce-Fe-B multilayers films was discussed.The growth mechanism for the out-of-plane orientation of Nd-Ce-Fe-B films was investigated in terms of the extended structure zone model.The following conclusions are showed as below:1.The anisotropic NdFeB nano-permanent thin films were prepared on Si substrate successfully,and the coercivity and energy product were more than 17 kOe and 52 MGOe,respectively,up to now the maximum value reported in the domestic literature.At the same time,CeFeB thin films with perpendicular anisotropy were also fabricated.It was found the best magnetic properties could be obtained for the CeFe B film with 200 nm thickness.2.The CeFeB nanofilms were systematically studied for the first time.Attempts to improve the magnetic properties of the CeFe B films by adding Nd layer,and the Nd atoms were found to successfully introduce into the CeFeB layer due to the thermal diffusion after post-annealing.The results showed the properties improved by depositing Nd at room temperature because of the improvement of boundary phase.When the Nd layer was deposited at room temperature,Nd atoms mainly entered the CeFe B layer by diffusing along the grain boundaries.Moreover,the best magnetic properties could be obtained for the CeFeB films which the thickness ratio of CeFe B layer and Nd layer was 20:3.3.The time dependence of Nd Fe B/CeFeB thin films was studied.The results shown that the magnetic viscosity coefficient decreased with the decrease of temperature,indicated both weakened thermal agitation and strengthened anisotropy energy were supposed to decrease transition frequency at low temperature.In addition,compared with magnetic viscosity coefficient of NdFe B and Ce FeB films over range of temperature?300 K?5 K?,the magnetic viscosity coefficient of NdFe B/CeFe B film can be effectively reduced by the combination of different hard magnetic layers.4.The growth mechanism of NdFeB/NdCeFeB films was discussed according to the extended structure zone model.The energy obtained by the post-deposition atoms decreased with the increase of the film thickness,and the actual structure zone of the films can be divided in zone?₀,zone T and zone I_c.The temperature gradient induced by thermal flow in the films contributed to the out-of-plane orientation of grains.Moreover,it was helpful to out-of-plane orientation by increasing the sputtering power,reducing the Ar gas pressure and shortening the distance between the substrate and the target.5.The effects of annealing temperature and Ta spacer layer on magnetic properties and magnetization behavior for Nd-Ce-Fe-B multilayers thin films were investigated.From the experimental results,the optimum annealing temperature range was 938?958K,and the roles of exchange coupling and magnetostatic coupling in the demagnetization process were clarified.This work also indicated that,using the proper thickness of Ta spacer layer,the magnetic properties can be enhanced for the Nd-Ce-Fe-B nanocomposite films by enhanced exchange coupling.