Development of A New Method of Preparing R-Fe-N Based Magnets

Sm_2Fe_&lt；17&GT；N_3基合金具有高居里温度、高饱和磁化强度和大的单轴磁各向异性等优异的磁性能，是高性能磁体材料的理想候选材料。然而，适用于实际应用的Sm-Fe-N磁体还没有制备出来。实用型磁体难以制备的主要原因是Sm_2Fe_(17)&Gt；N_3化合物的制备工艺困难。因此，本项目的目的是开发一种新的方法，直接从Sm_2Fe_&lt；17&gt；N_3合金中制备Sm_2Fe_&lt；17&gt；N_3化合物磁体，而不需要使用传统的粉末冶金和气体吸收工艺。因此，我们采用了反应气相沉积的最佳方法之一--激光沉积法。在此基础上，通过改变靶成分、气体种类和气压、衬底温度、后沉积热处理温度等沉积条件，制备了Sm-Fe-N薄膜。主要研究结果总结如下：1.研究成果。在氮化气氛中沉积的薄膜在其体内含有氮。然而，在我们的沉积条件下：靶成分为10-14at.%Sm，衬底温度为20-400ﾟC，氮气为N_2或NH_3，氮化气体为N_2或NH_3时，薄膜中的氮不是以SMN的形式存在。在真空或低压(5mTorr NH_3)中沉积的Sm_2Fe_(？)lt；17&Gt；N_3薄膜经热处理和氮化处理得到Sm_2Fe_(？)lt；虽然得到的薄膜具有矫直力，但其值比传统方法得到的值要小得多。因此，在此过程中应抑制α-Fe的析出。

Sm_2Fe_<17>N_3 based alloys are promising candidates for high performance magnet materials because of their superior magnetic properties such as high Curie temperature, high saturation magnetization, and large uniaxial magnetic anisotropy. However, Sm-Fe-N magnets applicable to practical uses have not been prepared. The difficult in preparing practical magnets can be attributed to the difficult in the preparation process of Sm_2Fe_<17>N_3 compound. Thus the purpose of this project is to develop a new method of preparing magnets based on Sm_2Fe_<17>N_3 compound directly from Sm_2Fe_<17> alloy without using the conventional powder metallurgy and gas absorption process.We started the research with using the sputtering method, but could not obtained desirable results. Thus we adopted the laser deposition method which is one of the best method for the reactive vapor deposition. Then, we prepared Sm-Fe-N films with varying deposition conditions such as the target compositon, the kind and pressure of gasses, the substrate temperature, and the after-deposition heat treatment temperature. Main results are summarized as follows.1. Films deposited in nitrogenating atmosphere include nitrogen in their bodies. However, nitrogen in the films exists in the form of SmN rather than Sm_2Fe_<17>N_3.2.Sm_2Fe_<17>N_3 films were not synthesized in the as-deposited state within our deposition conditions : the target composition of 10-14at.%Sm, the substrate temperature of 20-400ﾟC,the nitrogenating gas of N_2 or NH_3, and the gas pressure of 0-100mTorr.3. Sm_2Fe_<17>N_3 was synthesized by the heat treatment of the films deposited in vacuum or low pressure (5mTorr NH_3)and the subsequent nitrogenation. Although the obtained films show the coercivity, its value is much smaller than that obtained by the conventional method. Thus the precipitation of alpha-Fe should be suppressed in the process.