Magnetization Dynamics In Synthetic Ferromagnetic Thin Films

Synthetic ferromagnets (SFMs) possess the same layer structure found in the widely studied synthetic antiferromagnets. This consists of two ferromagnetic (FM) layers separated by a nonmagnetic (NM) spacer forming the structure FM1/NM/FM2, but SFMs describe the case where the interlayer exchange coupling promotes the parallel alignment of the magnetizations of the FM layers. The frequency and phase of the dynamic response of these structures depends sensitively on the interlayer exchange coupling as well as on the individual layer magnetizations. Through experiments and numerical simulations, we show that the dynamic response of the two ferromagnetic layers has an orthogonal dependence on the difference in layer magnetization and interlayer coupling allowing both parameters to be determined accurately. In addition, we are able to obtain the phases of the resonant modes, a hitherto challenging measurement, and thus show that the conventional acoustic and optical description does not fully capture the intricacies of SFM dynamics. These findings are directly applicable to the creation of tailored SFMs for spintronic devices such as STT/SOT-MRAM where magnetization and interlayer coupling are key parameters.