AVS 49th International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI-WeM

Paper MI-WeM4
High Frequency Noise Measurements in Spin-Valves

Wednesday, November 6, 2002, 9:20 am, Room C-205

Session: Magnetic Recording: GMR, Tunneling, and Media
Presenter: N.A. Stutzke, Boise State University
Authors: N.A. Stutzke, Boise State University
S.E. Russek, NIST, Boulder
S.L. Burkett, Boise State University
Correspondent: Click to Email
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 sub-micrometer magnetic devices.@footnote 1@ High-frequency magnetic noise arises from intrinsic thermal fluctuations of the device magnetization. High-frequency noise spectroscopy provides a powerful tool to characterize the dynamics and response of multilayer magnetic devices. In this study, the noise characteristics of micrometer-dimension spinvalves have been investigated at frequencies in the range of 0.1-6 GHz. 1/f noise dominates at frequencies below this range. High-frequency noise measurements as a function of temperature, bias current, and magnetic field are obtained for IrMn-exchange biased spinvalves using a 50 GHz spectrum analyzer, low-noise amplifier, and a cryogenic microwave probing system. Temperature is varied from 100-400K. 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.@footnote 2@ Noise is observed to shift to higher frequencies and decrease in amplitude with decreasing temperatures. This is consistent with an increase in magnetostatic anisotropy due to the increase in the saturation magnetization as the temperature is lowered. 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 constant (a smaller ferromagnetic resonance linewidth) and show additional features due to the presence of additional magnetostatic modes. @FootnoteText@ @footnote 1@N. Smith and P. Arnett, Appl. Phys. Lett. 78, 1448 (2001).@footnote 2@N. Smith, J. Appl. Phys. 90, 5768 (2001).