Comparison of angular coercivity in various magnetic media (abstract)

Abstract

Angular coercivity provides a method for studying magnetization-reversal mechanisms and has stimulated theoretical interests particularly for recording materials.1 This paper reports our experimental results on the angular variation of coercivity in different magnetic media prepared by various means, and compares these data. These include CoNiCr/Cr-type longitudinal media and Ba-ferrite–type particulate longitudinal media for hard-disk applications, and CoNi-type oblique evaporated longitudinal media for video recording. Results from sputtered CoNiCr/Cr media showed a symmetric M-type curve and the peak height decreased with intergranular coupling.2 In addition, the peak position also changed systematically with grain decoupling. M-type curves were also observed when the underlayer Cr thickness was varied, but the peak location remained unchanged. Results from Ba-ferrite media prepared with different packing densities exhibit similar curves as those for CoNiCr/Cr media. However, oriented Ba-ferrite media prepared by having a magnetic field applied at 30° and 60° with respect to the film plane show a very unique behavior. In contrast, CoNi films which were prepared by oblique evaporation in the presence of oxygen showed a canted columnar morphology with an easy axis of magnetization out of the film plane. The resultant angular coercivity featured a shifted M-type unsymmetric curve, and the shift angle increased with the oxygen content in the film. It is noted that at high O2 concentrations the curve deviates significantly from a shifted M-type nature. The microstructures of the aforementioned media will also be discussed.