Defect Related Switching Field Reduction in Small Magnetic Particle Arrays

An array of 42 μm square, 3 μm thick garnet particles has been studied. The strong crystalline uniaxial anisotropy of these particles results in the stable remanent state being single domain with magnetization parallel to the film normal. Magnetooptic measurements of individual particles provide distribution statistics for the easy-axis switching field Hsw, and the in-plane hard-axis effective anisotropy field, Heff , which induces the formation of a metastable stripe domain structure. Both Hsw and Heff are much smaller than the crystalline anisotropy field. Micromagnetic simulations show that the small Hsw cannot be attributed to shape anisotropy, but is consistent with smooth, localized reductions in the crystalline anisotropy caused by defects in either the particles or the substrate.