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High-frequency noise measurements in spin-valve devices

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3 Author(s)
Stutzke, N.A. ; Boise State University, Boise, Idaho 83725 ; Burkett, S.L. ; Russek, S.E.

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High-frequency magnetic noise in magnetoresistive devices being developed for read-sensor and magnetic random access memory applications may present fundamental limitations on the performance of submicrometer magnetic devices. High-frequency magnetic noise (HFN) arises from intrinsic thermal fluctuations of the device magnetization. High-frequency noise spectroscopy provides a powerful tool to characterize the dynamics and response of small multilayer magnetic devices. In this study, the noise characteristics of micrometer-dimension spin valves have been investigated at frequencies in the range 0.1–6 GHz. At frequencies below this range 1/f noise dominates. HFN measurements, as a function of bias current and longitudinal magnetic field, are obtained for IrMn exchange-biased spin valves using a 50 GHz spectrum analyzer, low-noise amplifier, and a microwave probing system. The magnetic noise is obtained by taking the difference between the noise spectrum of the device in a saturated and unsaturated state. The data can be fit to simple models that predict the noise power to be proportional to the imaginary part of the free-layer magnetic susceptibility. There are some important differences between the high-frequency noise measurements and direct measurements of the device susceptibility (both at the device and wafer level). The noise measurements show a smaller damping parameter (a smaller ferromagnetic resonance linewidth) and additional features due to the presence of nonuniform modes. © 2003 American Vacuum Society.

Published in:

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films  (Volume:21 ,  Issue: 4 )