Temperature and Field Dependence of High-Frequency Magnetic Noise in Spin Valve Devices
N. A. Stutzke, S. L. Burkett, Stephen E. Russek
High-frequency noise of micrometer-dimension spin valve devices has been measured as a function of applied field and temperature. The data are well fit with single-domain noise models that predict that the noise power is proportional to the imaginary part of the transverse magnetic susceptibility. The fits to the susceptibility yield the ferromagnetic resonance (FMR) frequency and the magnetic damping parameter. The resonant frequency, increases from 2.1 to 3.2 GHz, as the longitudinal field varies from -2 to 4 mT and increases from 2.2 to 3.3 GHz as the temperature decreases from 400 to 100 K. The shift in the FMR frequency with temperature is larger than that expected from the temperature dependence of the saturation magnetization, indicating that other temperature- dependent anisotropy energies are present, in addition to the dominant magnetostatic energies. The measured magnetic damping parameter α decreases from 0.016 to 0.006 as the temperature decreases from 400 to 100 K. The value of the damping parameter shows a peak as a function of longitudinal bias field, indicating that there is no strict correlation between the damping parameter and the resonant frequency.