Magnetization of Chromium Dioxide Particles Plated with Cobalt

Abstract

The coercivity of an acicular chromium dioxide powder remarkably increased when electroless cobalt plating was applied to it by using cobalt sulfate. A particlesize of the chromium dioxide powder, starting material, was 0.8μ in length, 1:15 in shape ratio, and the magnetic properties of the powder were 92emu/g in saturation magnetization (σ_a) and 500Oe in coercive force at 10 kOe of applied field. Plating solution was a cobalt(II) sulfate solution containing sodium phosphinite as a reducing agent. During an experiment, the bath was stirred sufficiently to bring about high dispersion of a particle. The bath temperature was kept at 80°C. The plating time varied from 0.5 to 10 minutes.The coercive force of particles remarkably increased to maximum, 970Oe, at the beginning of aplatingas shown in Fig. 2. It might be possible that an increase in coercivity of particles is caused by bonding of chromium with cobalt via oxygen ion, for instance, Co-O-Cr, Co-O-Co etc. and notpossible that an increase in coercivity neither depends on a decrease in a particle interaction nor on an increase in a magnetostriction of a particle.The temperature dependence of the coercivity and the magnetization of cobalt plated particles has been more improved than that of, original chromium dioxide particles.