Dependence of magnetic properties on grain size of α-Fe in nanocomposite (Nd, Dy)(Fe, Co, Nb, B)5.5/α-Fe magnets

For the nanocomposite magnets (Nd0.9Dy0.1)(Fe0.77Co0.12Nb0.03B0.08)5.5/α-Fe, the best magnetic properties were obtained with the average grain size of α-Fe d=15 nm and with the content of α-Fe cm=45 wt % that is well below the structural percolation threshold of the soft magnetic phase. The measured dependence of the coercivity on the grain size of α-Fe tends to indicate that the optimum grain size dop increases with increasing α-Fe content, for cm>30 wt %. If d>dop, contracted hysteresis is formed; if d<dop/2, the coercivity rapidly decrease due to possible coupling between hard magnetic grains situated at two sides of a soft grain.