Synthesis of Sm2Fe17N3 compacts by mechanical milling with graphite powder and their magnetic properties

It is difficult to prepare Sm₂Fe₁₇N₃ sintered magnets because Sm₂Fe₁₇N₃ phase decomposes above 600 °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.