Research and development of exchange spring magnet by means of micro-alloying technique

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The main purpose of this study is to reveal the roles of small amount of additives in the exchange spring magnets. Small additives sometimes drastically reduce grain size of crystallites in the crystallization from amorphous states. Here we have mainly investigated the changes of local structures of small additives by fluorescence XAFS during crystallization from amorphous states and during hydrogenation. It has been found that Ga in Fe_<73>Ga_4Nb_3Si_<11>B_9 moves toward interface of precipitated alpha-Fe at an early stage of crystallization, and then included into alpha-Fe with the crystallization being proceeded. We also studied the local structure changes of Ga and Zr in Nd_<13.6>Fe_<68.2>Co_<10.8>Ga_<1.0>Zr_<0.1>B_<6.9> before and after hydrogenation. Before hydrogenation Ga is included in Nd_2Fe_<14>B and after hydrogenation it moves into alpha-Fe. On the other hand Zr makes selective bonding to hydrogen and forms ZrH_2 after the hydrogenation.At the present stage how such behaviors of Ga and Zr in HDDR are related with the crystalline memory effects are not yet clear. Further investigations are needed to reveal it.