<i>In situ</i>ferromagnetic resonance in coupled ultrathin trilayers with perpendicularly oriented easy axes

Abstract

Ultrathin ferromagnetic trilayers with perpendicularly oriented easy axes—one film in-plane the other out-of-plane—attracted recent interest in the study of interlayer exchange coupling, domain formation, and canted magnetization orientation. To investigate and understand the thermodynamic ground state of such a prototype trilayer we employed in situ ferromagnetic resonance (FMR) for a Ni/Cu/Co/Cu(001) trilayer. The FMR polar angular dependence has been measured and analysed in the framework of the Landau–Lifshitz equation. In addition the thickness of the Cu spacer layer has been changed to manipulate the strength of the interlayer exchange coupling and select between ferromagnetic and antiferromagnetic coupling. The FMR experiment yields—unlike other techniques—the coupling strength and anisotropy energy in absolute energy units. This gives also a full insight into all the parameters governing the ground state free energy, the equilibrium angles of the canted magnetization, as well as the optical and acoustical mode formed by the two uniform spin-wave excitations.