Weak ferromagnetic interaction between magnetic layers studied by X-ray ferromagnetic resonance

X-ray Magnetic Circular Dichroism(XMCD) provides useful information about a spin angular momentum of a magnetic element. X-ray ferromagnetic resonance(XFMR) can measure a precessional motion of magnetization of each element when it is combined with XMCD. When the dynamics of multilayered thin film composed of different magnetic elements is measured using XFMR, precessional motions of each layers can be observed separately. We inserted a normal metal (Ti) between the thick magnetic layer (Py) and the thin magnetic layer (CoFeB) to evaluate an interaction between the magnetic layers. The interaction between the two layers was observed until the thickness of Ti reached 10 nm. We simulated the ferromagnetic resonances of these two layers using two Landau-Lifshitz-Gilbert equations to determine the type and strength of the interaction. A ferromagnetic coupling between the two magnetic layers was observed, and the smallest interaction amplitude was estimated to be ~1.2 μJ/m² with Ti (10 nm) insertion layer.