Magnetic force microscopy study of microwave-assisted magnetization reversal in submicron-scale ferromagnetic particles

Changes in magnetic-domain configurations caused by the application of radio-frequency (rf) fields ranging from 3 to 18 GHz were observed using magnetic force microscope. rf fields barely altered the magnetization of Co particles with scattered large crystalline anisotropy; however, for NiFe particles, magnetization switching occurred when the rf approached the natural ferromagnetic-resonance frequency of 5.92 GHz. However, the reduction of the switching field fluctuated widely among the particles. Scattering of the effective energy barrier to thermal fluctuations caused by an applied rf field can explain the stochastic switching properties.