Domain wall and microwave assisted switching in an exchange spring bilayer

We explore the response of a magnetic bilayer to a driving microwave field using micromagnetic simulations. The bilayer consists of 8 nm of a material with a high uniaxial anisotropy and 56 nm of a material with a lower uniaxial anisotropy. The width and length of the structure is 100 x 100 square microns. A small applied field, opposite to the magnetization, switches most of the lower anisotropy material but not the higher anisotropy material, forming a domain wall between the two materials. We evaluate the frequencies of the magnetic eigenmodes for the entire system using Fourier analysis and then drive the structure with an oscillating magnetic field at each of the eigenfrequencies. When the oscillating microwave field is added, the static switching field required to align both layers is decreased compared to the undriven case. With a driving field strength of 120 Oe the switching field is reduced by about 40%, from 1.12 kOe for the undriven case to 0.55 Oe for the driven case. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3573497]