Magnetic switching and uniaxial anisotropy in lithographically defined anti-dot Permalloy arrays

The magnetic switching of a continuous Permalloy film is artificially modified by lithographically structuring an anti-dot array. The anti-dots introduce a spatially variant shape anisotropy field which competes with the intrinsic uniaxial anisotropy of the continuous him. This results in two different spin reversal mechanisms, depending on the relative orientation of the applied magnetic field and the intrinsic anisotropy axes and which have been observed by scanning Kerr microscopy. When the field is applied along the intrinsic easy axis, reversal proceeds by the sweeping of two 180 degrees domain walls (DWs) through the sample. The anti-dots become the dominant DW pinning sites which leads to a slight increase in the coercivity. This could be used in the future as a way of artificially controlling coercivity. When the field is applied along the intrinsic hard axis, a well defined periodic domain structure occurs at remanence. This could be significant for high density data storage. A micromagnetic calculation explains the two reversal mechanisms and indicates optimum anisotropy conditions for data storage applications.