DEPENDENCE OF COERCIVITY ON PARTICLE-SIZE IN SM2FE17N3 POWDERS

The coercivity of Sm2Fe17N3 particles varies as the inverse of the average particle size D, when 1 mu m<D<50 mu m. The variation in coercivity H-c=2H(a)L(0)/D, where H-a is the anisotropy geld of Sm2Fe17N3, is explained in a model where there is a random spatial distribution of nucleation centers whose average separation L, is equal to 120 nm and whose size follows a 1/r(4) power law. Hysteresis has been measured as a function of tile angle a between the alignment direction and the applied field for aligned powder samples with D=3.0, 4.4, 5.8, 13 and 52 mu m. It has a 1/cos theta dependence.