Configurational stability of patterned magnetic nanosystems

The stability of the magnetic state of individual elements within patterned nanoarrays depends on the balance of interelement interactions and shape anisotropy. These effects were studied by ferromagnetic resonance and alternating gradient magnetometry to characterize large area hexagonal arrays of 20 nm thick 190 nm wide elliptical Permalloy elements with aspect ratios 1.6 and 3.6, made using interference lithography, electron beam evaporation, and lift-off processing. The in-plane anisotropy of short ellipses is 42 mT, as compared to the 86 mT in-plane anisotropy of ellipses twice as long. The out-of-plane anisotropy field is about 650 mT, similar for both systems. Separation dependence of the interelement interactions was modeled numerically. The significant contribution from far neighbors to the interaction field is about 20 mT, comparable to the switching field of soft magnetic materials.