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

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Abstract
Dynamic magnetic properties in perpendicularly exchange-coupled [Co/Ni]5/Cu(tCu=0-2 nm)/TbCo structures show strong dependences on the interfacial AFM strength Jex controlled by the Cu interlayer thickness. The precession frequency f and effective damping constant αeff of [Co/Ni]5 multilayer differs distinctly for parallel (P) and antiparallel (AP) magnetization orientation states. For samples with a thin tCu, f of AP state is apparently higher while αeff is lower than in 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 tCu increasing. 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.
Funding Information
  • Ministry of Science and Technology of the People's Republic of China (2014CB921104)
  • National Natural Science Foundation of China (11474067, 11674095, 51671057)

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