Direct measurement of spatially localized ferromagnetic-resonance modes in an antidot lattice (invited)

Abstract

Recent ferromagnetic-resonance (FMR) measurements and related simulations on antidot structures suggested the existence of spatially localized modes. In this report we confirm the existence of these modes using time-resolved Kerr microscopy (TRKM) as a local probe of the magnetodynamics. FMR measurements on an antidot array (a 40 - nm -thick permalloy film with a hole size of 1.5 μ m and a hole lattice spacing of 3 μ m × 5 μ m ) at frequencies between 10 and 35 GHz reveal two main resonances, whose relative amplitudes and orthogonal uniaxial in-plane anisotropies suggest the existence of modes localized between holes along each of the principal axes. TRKM measurements in applied fields ranging from 100 to 600 Oe show explicitly the existence of these two modes—one at low frequency between the holes along the short axis and one at higher frequency between the holes along the long axis. TRKM also reveals additional mode structure, most notably a low-frequency mode localized along the edges of the antidots, similar to the edge modes observed in magnetic wires.