Comparison of angular variation of coercivity in various magnetic media

Abstract

Angular variation of coercivity provides a method for studying magnetization reversal mechanisms and has stimulated theoretical interest, particularly for recording materials. This paper reports our experimental results on the angular variation of coercivity in different magnetic media, and compares these data. These include CoNiCr/Cr-type longitudinal media and Ba-ferrite-type particulate longitudinal media for hard disc applications, and CoNi-type metal evaporated longitudinal media for video-recording. Results from sputtered CoNiCr/Cr media showed a symmetric M-type curve and the peak height decreased with inter-granular coupling. In addition, the peak position also changed systematically with grain decoupling. Results from Ba-ferrite particulate media exhibited curves similar to those for CoNiCr/Cr media having relatively magnetically uncoupled grains. However, oriented Ba-ferrite media prepared by having a magnetic field applied at 30 and 60° with respect to the film-plane, showed a very interesting 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 features a shifted M-type unsymmetric curve and the shift angle increased with the oxygen content in the film - similar to the oriented Ba-ferrite media. It was 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.