Spin-torque driven ferromagnetic resonance of Co/Ni synthetic layers in spin valves

摘要

Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study thinCo/Ni synthetic layers with perpendicular anisotropy confined in spin-valvebased nanojunctions. Field swept ST-FMR measurements were conducted with amagnetic field applied perpendicular to the layer surface. The resonance lineswere measured under low amplitude rf excitation, from 1 to 20 GHz. Theseresults are compared with those obtained using conventional rf field driven FMRon extended films with the same Co/Ni layer structure. The layers confined inspin valves have a lower resonance field, a narrower resonance linewidth andapproximately the same linewidth vs frequency slope, implying the same dampingparameter. The critical current for magnetic excitations is determined frommeasurements of the resonance linewidth vs dc current and is in accord with theone determined from I-V measurements.