Magnetic interaction in spherical barium ferrite particle tape

New spherical and conventional hexagonal platelet-shaped barium ferrite (BaFe) particles were dispersed and hand-coated onto polyethylene terephthalate (PET) film. Curves of ΔM(H), the change of magnetization as a function of magnetic field, were calculated from measurements of the d and r components M_d(H) and M_r(H). This was done to evaluate particle-to-particle magnetic interactions. The oriented platelet-shaped particles showed a large and relatively broad positive ΔM(H) peak, which develops from particle stacking. The oriented spherical BaFe particles gave completely different ΔM(H) curves with a much smaller and narrower positive peak, and an equally small and narrow negative peak. The unoriented platelet-shaped BaFe produced ΔM(H) curves having a small positive peak followed by a small but broader negative peak. This has been explained in terms of randomly oriented stacks. It was suggested that the positive peak develops from particle-to-particle interactions within the stacks, and the negative peak results from interactions between stacks. The unoriented spherical BaFe particle gave a ΔM(H) curve having a broad negative peak, similar to what is observed with acicular metal particles