Origin of four-fold anisotropy in square lattices of circular ferromagnetic dots
Abstract
We discuss the four-fold anisotropy of in-plane ferromagnetic resonance (FMR) field Hr, found in a square lattice of circular Permalloy dots when the interdot distance a gets comparable to the dot diameter d. The minimum Hr, along the lattice <11> axes, and the maximum, along the <10> axes, differ by 50 Oe at a/d = 1.1. This anisotropy, not expected in uniformly magnetized dots, is explained by a non-uniform magnetization () in a dot in response to dipolar forces in the patterned magnetic structure. It is well described by an iterative solution of a continuous variational procedure.
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