High-frequency measurements of spin-valve films and devices, made using several different measurement techniques, are presented and compared. Pulsed inductive measurements were made on sheet films and provide insight into the intrinsic dynamical properties of the component films and the multilayer stacks. The damping parameter, in the completed spin-valve stack, is larger than in the constituent films, and the damping exhibits a strong dependence on the easy-axis magnetic field. Direct time and frequency domain measurements of the dynamical response of micrometer-size spin-valve devices, made using high-bandwidth magnetoresistance techniques, showed damping parameters comparable to the measurements on spin-valve sheet films. The small-angle magnetization response was also determined by high-frequency magnetic noise measurements. The damping parameters were smaller than those obtained by direct susceptibility measurements. The device-level measurements show a different dependence of the damping parameter on the easy-axis field as compared to sheet-level measurements. In addition to the uniform rotation mode, other peaks can be observed in the noise spectra that correspond to fluctuation modes arising from micromagnetic structure. Electrical device measurements have much greater sensitivity than other high-frequency magnetic measurement techniques, which allows the direct observation of magnetization motion in sub-micrometer elements without averaging. This technique is used to directly examine thermally activated events and non-repetitive dynamical motions.
Citation: Journal of Applied Physics
Pub Type: Journals
damping parameter, magnetic noise, magnetization motion, magnetoresistance