Giant Near-90° Coupling in Epitaxial CoFe/Mn/CoFe Sandwich Structures

Trilayer samples of CoFe/Mn/CoFe(001) have been prepared by molecular beam epitaxy and investigated by magnetometry and ferromagnetic resonance (FMR). Very strong near-90° coupling (up to 2.5 ergs/c${\mathrm{m}}^2$) between the CoFe layers, with no evidence for 180° coupling, was found in all but the thickest Mn-layer samples. The field dependence of the magnetization requires that the coupling energy have the algebraic form $F_c{=C}_{+}({\phi }_1-{\phi }_2{)}^2{+C}_{-}({\phi }_1-{\phi }_2-\pi {)}^2$ suggested recently for antiferromagnetic interlayers. The observed angular dependence of both the acoustic and optical FMR modes found can be described by this model.