The Fabrication And Magnetic Properties In Nd₂Fe₁₄B Based Nano-permanent Magnetic Thin Films

The Nd-Fe-B permanent magnetic films with high coercivity,which have been mainly applied in the micro-electro-mechanical system(MEMS),have been increasingly studied in order to meet the requirement of high performance and reliability of MEMS.In this work,Nd-Fe(Nd-rich)/Nd-Fe-B(Fe-rich)bilayer and multilayer films were prepared by magnetron sputtering.The permanent magnetic properties were obtained through the post annealing.The effect of substrate,buffer(or capping)layer,annealing temperature,compositions of the targets on the magnetic properties were discussed systematically;the dependence of buffer(or capping)layer was investigated from the aspects of elements’ diffusion,distribution,and mutual combining;the kink of the second quadral demagnetized curve was weakened by adjusting the thickness of magnetic layer,inserting the isolation layer and multi-layered mode;The main work is briefed as follows:1.Through optimizing substrate and buffer(or capping)layer,it had been found that the Ta buffer(or capping)layer is helpful for obtaining the better magnetic performances while the Nd-Fe/Nd-Fe-B films were deposited on Si substrate.Based on this,the composition of the films was tuned through changing the target composition.The Nd-Fe/Nd-Fe-B films with the designed Nd8Fe84B8 target possessed the high coercivity value of 19.2 k Oe after annealing at 600 ℃.Moreover,the and had been enhanced significantly(=6.3 kG,=8.2 kG).2.Based on the analysis of structure,diffusion and combination of elements of Nd-Fe/Nd-Fe-B films,it had been found that the distributions of all the elements in the Nd-Fe/Nd-Fe-B films significantly changed under the annealing.The hard phase Nd2Fe14 B mainly gathered within the Nd-Fe-B layer.A soft phase Fe-Ta-B amorphous layer formed at the Ta/Nd-Fe and Nd-Fe-B/Ta layers’ interface,leading to the emergence of kink in the hysteresis loop due to the weakened exchange coupling effect.In addition,the kink became worse with increasing the annealing temperature.3.The thickness of the magnetic films and the annealing temperature were optimized.On the basis of Nd-Fe(36 nm)/Nd-Fe-B(41 nm)thin film annealed at 600 ℃,the Pr-Cu was selected as the isolation layer considering the influence of buffer(or capping)layer on the magnetic properties.After inserting Pr-Cu layer with the thickness of 4 nm,the kink absolutely disappeared and the relevant hard magnetic properties parameters were achieved: ? =0.97,(8=26.5 kOe and()8)(6=4.1 MGOe.Additionally,the([Nd-Fe/Nd-Fe-B]n)multilayer cycling structure was also performed to further improve the magnetic properties and weaken the effect of the kink.While the cycle number of n=4 for the multilayer film,the kink completely disappeared: ? was close to 1,the (8=19.8 kOe and the()8)(6=5.1 MGOe,respectively.Through the depth-profiling XPS analysis,it could be found that the elements could well diffuse between the interlayer and interfaces in the [Nd-Fe/Nd-Fe-B]n multilayer cycling structure,which could reduce the enrichment of Fe,B at the interface of Ta/magnetic layer,enhancing the formation of Nd2Fe14 B hard phase in the whole magnetic layer to improve the magnetic performance.