Dependence of coercivity on phase distribution and grain size in nanocomposite Nd2Fe14B/α-Fe magnets

The dependence of coercivity on the grain size in nanocomposite Nd2Fe14B/alpha-Fe magnets with different distributions of magnetically soft and hard phases is investigated by means of statistical mean. The calculations show that when there exists no soft phase, the coercivity of magnets decreases monotonically with hard grain size reducing. For a given volume fraction of hard phase, the coercivity of nanocomposite Nd2Fe14B/alpha-Fe magnets with a random distribution of soft and hard grains shows a peak value as a function of hard grain size. When the hard grain size is larger than an optimum value of soft grain size (15nm), the nanocomposite Nd2Fe14B/alpha-Fe magnets with the multilayer structure of soft and hard grains can possess a higher coercivity than that with the random distribution of soft and hard grains.