Brillouin light scattering study of magnetic coupling in CoFe/Mn/CoFe

Coupling mechanisms between ${\mathrm{Co}}_{0.75}{\mathrm{Fe}}_{0.25}$ films separated by Mn layers are investigated using Brillouin light scattering from thermal spin waves. Trilayers of CoFe/Mn/CoFe, grown by molecular-beam epitaxy, were studied with Mn thicknesses between 6 and 30 Å. Spin-wave excitations corresponding to acoustic and optic modes in double layer magnetic structures were observed, and allowed a determination of a strong magnetic coupling between the CoFe films. Spin-wave frequencies were examined as functions of applied field, Mn film thickness, and temperature. A microscopic model is used to examine magnetic order in a ferromagnet/antiferromagnet/ferromagnet structure. Discrepancies between the data and predictions of the microscopic model provide evidence for a twist in the FeCo spins that extends into the ferromagnet layer.