Controllable Interfacial Coupling Effects on the Magnetic Dynamic Properties of Perpendicular [Co/Ni]5/Cu/TbCo Composite Thin Films.

Dynamic magnetic properties in perpendicularly exchange-coupled [Co/Ni]5/Cu (tCu = 0-2 nm)/TbCo structures show strong dependences on the interfacial antiferromagnetic strength Jex, which is controlled by the Cu interlayer thickness. The precession frequency f and effective damping constant αeff of a [Co/Ni]5 multilayer differ distinctly for parallel (P) and antiparallel (AP) magnetization orientation states. For samples with a thin tCu, f of the AP state is apparently higher, whereas αeff is lower than that in the P state, owing to the unidirectional exchange bias effect (HEB) from the TbCo layer. The differences in f and αeff between the two states gradually decrease with increasing tCu. By using a uniform precession model including an additional HEB term, the field-dependent frequency curves can be well-fitted, and the fitted HEB value is in good agreement with the experimental data. Moreover, the saturation damping constant α0 displays a nearly linear correlation with Jex. It decreases significantly with Jex and eventually approaches a constant value of 0.027 at tCu = 2 nm where Jex vanishes. These results provide a better understanding and effective control of magnetization dynamics in exchange-coupled composite structures for spintronic applications.