Synthesis of Sm_2Fe_(17)N_3 compacts by mechanical milling with graphite powder and their magnetic properties

摘要

It is difficult to prepare Sm2Fe17N3 sintered magnets because Sm2Fe17N3 phase decomposes above 600 degrees C, and the decomposition results in significant reduction of magnetic properties. To consolidate Sm2Fe17N3 powder below the decomposition temperature, an increase of the filling fraction is expected to be one of the effective methods. In this study, an addition of graphite as well as Zn to Sm2Fe17N3 powder was conducted by mechanical milling. The dispersion of graphite powder, which acted as a lubricant when compacting the powder, resulted in an increase in the filling fraction. The high relative density, 93.0%, of a sintered body was easily obtained by the addition of the most balanced amounts of graphite and Zn. The magnetization was increased with increase in the additive amount of graphite due to the reduction of the strain accumulated to crystal grains during the mechanical milling. The coercivity was not decreased even when the amount of Zn was reduced, because the Zn powder was dispersed more homogeneously due to the suppression of agglomeration among particles and adhesion of powder to the inside wall of pod during the mechanical milling by the addition of graphite powder.