Nucleation and pinning mechanisms in sintered SmCo5magnets

Nucleation and pinning mechanisms in sintered SmCo5magnets have been investigated using the Kerr magneto-optic effect and conventional demagnetization measurements. It has been shown that changes in the total grain boundary area produced by grinding the sintered material do not correlate directly with the resulting decrease in coercivity. Observations of the domain structures during demagnetization end subsequent remagnetization indicate that most grains are controlled by a type of nucleation which involves immediate reversal of the magnetization of the grain at a critical nucleation field. Evidence is also presented which shows that domain walls can be strongly pinned within grains and that a further increase in the field is required for their removal. There is also considerable asymmetry in the behaviour of individual grains since the application of a given field in one direction produces a different result from that when the field is applied in the opposite direction. Preliminary measurements on the grain boundaries by scanning electron probe micro-analysis show that they are samarium rich.