FACTORS CONTROLLING THE COERCIVITY OF ND-FE-B TYPE PERMANENT-MAGNETS

The variations of coercivity of Nd-Fe-B type permanent magnets have been investigated. It is shown that there exists a simple relation among the coercivity of annealed Nd-Fe-B magnets Hc, the anisotropy field HA and the spontaneous magnetization Is of the hard magnetic Nd2Fe14B phase: μ0Hc=Ne(μ0kHA-NiIs), where k and Ni are two constants related to the completeness of the Nd2Fe14B grain surface layers and the local demagnetization fields of isolated grains, respectively, and Nc is a parameter describing the magnetic interactions between the Nd2Fe14B grains. It is estimated that the values of k and Ni are about 0.6 and 1.8, respectively, and that the coercivity of an isolated Nd2Fe14B grain is about 2 T at room temperature.