We measure a shape dependent anisotropy energy in isolated square permalloy dots with characteristic dimensions as small as 200 nm. The magnetization behavior is characterized using the anisotropic magnetoresistance to determine the magnetic state of the sample. The behavior is consistent with the sample adopting a quasi-single-domain magnetization with a direction determined by an anisotropy intrinsic to the square geometry. We quantify the magnitude of this anisotropy through two independent measurements and confirm the observed magnetic behavior with micromagnetic simulations.
Bibliographical noteFunding Information:
This work was supported primarily by ONR Grant N00014-11-1-0850 and the MRSEC Program of the NSF under Grant No. DMR-0819885. Part of this work was carried out in the University of Minnesota's Nanofabrication Center, which receives partial support from NSF through the NNIN program, and Characterization Facility, a member of the NSF-funded Materials Research Facilities Network via the MRSEC program. D.E. acknowledges the support of a University of Minnesota Fellowship.