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

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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.