Dynamics of weak magnetic coupling by x-ray ferromagnetic resonance

We investigate the interaction between two magnetic layers separated with a normal metal insertion layer (Ti, Pt, and Ru) using x-ray ferromagnetic resonance (XFMR). We measure the amplitude and phase of the ferromagnetic resonance of both layers. Our results indicate that a ferromagnetic exchange coupling between two layers is a dominant coupling mechanism for a thick insertion metal layer. Based on the exchange coupling model, we extract the smallest value of the indirect exchange coefficient of 1.2 μJ/m2, which corresponds to an exchange field of about 0.36 mT. While this value is difficult to measure with other experimental tools, we were able to measure the small value because XFMR detects a resonance phenomenon of a thin layer generated by an oscillating indirect exchange and the Oersted fields with a phase and layer resolved observation.