Ferromagnetic resonance study of nanoscale ferromagnetic ring lattices

Square lattices of permalloy rings with different inner diameters (D-i) were fabricated by electron beam lithography and investigated by ferromagnetic resonance (FMR). Results reveal that FMR spectra are sensitive to the ring dimensions. A large shift of the uniform mode from 1200 to 1800 Oe, and a dramatic decrease in its intensity are observed as D-i increases from 0 to 300 nm. Other resonance peaks at fields slightly below the uniform mode greatly increase in intensity and shift to lower field with increasing D-i. An isolated resonance below 200 Oe is also observed. Possible reasons for these variations are discussed. (C) 2004 American Institute of Physics.