Mechanism for coercivity in splat-cooled RCo5 compounds

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Abstract
Splat‐cooling technique is used to prepare fine powders of certain RCo5 compounds. Powders produced in this way are free from most of the defects that are introduced in powders prepared by mechanical grinding. Furthermore, splat‐cooled materials are shown to have large concentrations of grain boundaries. These powders have magnetic properties which are different from those of the powders produced by mechanical communication. In particular, the intrinsic coercivities of PrCo5 and MMCo5 are increased significantly by splat cooling, while their maximum energy products are reduced. Heat treatments of splat‐cooled powders, which reduces the density of grain boundaries, increases coercivity slightly but a large increase takes place in the maximum energy product. Mechanical grinding of splat‐cooled materials produces similar effects, although this time it is due to the deliberate introduction of defects which act as pinning centers. By analyzing the hysteresis curves of as‐ground, splat‐cooled and heat‐treated or ground splat‐cooled SmCo5 we have concluded that in the splat‐cooled materials a nucleation mechanism is dominant in the initial stages of the magnetization reversal process. Nucleation takes place at the grain boundaries which are in abundance.

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