ANGULAR VARIATION OF THE COERCIVE FORCE AND REMANENCE IN BOROHYDRIDE REDUCED IRON PARTICLES

The angular dependence of the coercive force and remanence on borohydride reduced iron particles was measured as a function of mulling time. Typically the saturation moment of the powder was 150 emu/gram, while the coercive force and remanence of the unoriented powder was 500 Oe and 0.48, respectively. 50% by weight of the powder was dispersed in an epoxy binder using mulling cycles N=0-300, spread on a polyimide film and oriented in a 2000 Oe field. The remanence in the parallel direction increased from 0.60 for N=0 to 0.74 for N=300. The remanence varied monotonically from a maximum in the parallel (cursive-theta sign=0°) to minimum in the perpendicular direction (cursive-theta sign=90°). The coercive force (Hc) showed a peak at cursive-theta sign=55° and showed a decrease at cursive-theta sign=0° and cursive-theta sign=90°. The coercive force decreased with mulling cycles and Hc(0°)/Hc(90°) <1. Ball milling the powder produced qualitatively the same results.