Configurational Anisotropy in Nanomagnets

A novel magneto-optical method has been used to probe the internal magnetic energy surface in $150\times 150\times 15{\mathrm{nm}}^3$ square ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{14}{\mathrm{Mo}}_5$ (“supermalloy”) nanomagnets which were fabricated by electron beam lithography. A strong fourfold symmetric anisotropy field of strength $365\pm 20\mathrm{Oe}$ is found, which confirms a recent prediction of the appearance of a configurational anisotropy due to the small deviations of the magnetization from the uniform state.