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

Sm_2Fe_<17>N_3基合金具有高居里温度、高饱和磁化强度和大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选择。然而，目前还没有制备出适用于实际用途的钐铁氮磁铁。实际磁体制备的困难可归因于Sm_2Fe_<17>N_3化合物制备过程的困难。因此，本课题的目的是在不采用传统的粉末冶金和气体吸收工艺的情况下，直接从Sm_2Fe_<17>N_3合金中制备Sm_2Fe_<17>N_3复合磁体。我们从使用溅射法开始研究，但没有得到理想的结果。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。然后，我们在不同的沉积条件下，如靶成分、气体种类和压力、衬底温度和沉积后热处理温度，制备了Sm-Fe-N薄膜。主要研究结果总结如下：沉积在氮化大气中的薄膜，其体内含有氮。膜中的氮以SmN的形式存在，而不是以Sm_2Fe_<17>N_3.2的形式存在。在我们的沉积条件下，Sm_2Fe_<17>N_3薄膜没有在沉积状态下合成：目标成分为10-14at。2 .衬底温度为20 ~ 400℃，氮化气体为N_2或NH_3，气体压力为0 ~ 100mtorr。将真空或低压（5mTorr NH_3）沉积的薄膜进行热处理，然后进行氮化，合成Sm_2Fe_<17>N_3。所得薄膜虽然显示矫顽力，但其值远小于常规方法所得的矫顽力。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.