Shape-induced biaxial anisotropy in thin magnectic films

Measurements taken in the presence of an orienting field were made on four-pointed star-shaped films etched from planar uniaxial films. These yielded large biaxial anisotropy terms. In analyzing the effect, this film was presumed to consist of small partitions (typically 500). Within each partition the magnetization was assumed to be uniform and in the plane of the film, but its direction was allowed to vary from partition to partition. The non-uniform spatial distribution over the whole film was obtained by numerically iterating to the minimum energy condition. The high-energy state occurred when the average was oriented from tip to tip in the star-shaped film, while the low-energy state corresponded to the average pointing diagonally (across the short dimension). The calculated biaxial anisotropy was then obtained under the assumption that all the energy difference between these two states can be attributed to the biaxial property of this film. The biaxial term is a result of the nonuniform distribution of , which is field dependent. The measured biaxial terms were obtained from torque measurements and were in good agreement with the calculated values.