Control of Permeability of CoB Soft Magnetic Films by Heat Treatment in a Magnetic Field

Abstract

An effort has been made to improve the properties and specifically the permeability μ, of CoB soft magnetic films produced by electroless plating by application of heat treatment in a 2 kOe magnetic field. The optimum treatment conditions were found to be 150°C for 30min with the field applied along the hard magnetization axis of the film, and this treatment increased μ to 2000. The magnetic anisotropy field Hk decreased from 40 Oe to 8 Oe. The microstructure of films treated at various temperatures was also investigated. As-plated films consisted of fine hcp crystallite grains about 100Å in diameter, and this was retained with treatment up to 300°C. At above 350°C, fine, uniform grains grew locally and the formation of an fcc phase was detected. It is suggested that the improvement in permeability was due to an appropriately low value of Hk for the conditions at which the fine crystal grains were retained.