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Anisotropic frequency response of spin-torque oscillators with applied field polarity and direction

Published

Author(s)

Matthew R. Pufall, William H. Rippard, Stephen E. Russek, Eric R. Evarts

Abstract

We have measured spin-torque-driven oscillations of Ni80Fe20 free-layer nanocontacts as a function of field direction. For a given field axis angle (10◦ from the surface normal) and magnitude, simply changing the field polarity can significantly alter the device output. The critical current Ic, the frequency of oscillation f , the amplitude, and the f vs current f (I ) all change with field polarity and change if the applied field axis is rotated about the surface normal. Spin-torque ferromagnetic resonance measurements show that the linear resonant frequency f and the slope of f (I ) at currents much less than Ic also vary by tens of MHz and tens of MHz/mA, respectively, with field polarity. These results are consistent with the idea that the mode excited by spin torque interacts strongly with a different subregion of the magnetization in the vicinity of the contact for each field direction, resulting in potential variations in the anisotropy field, Oersted field, and spin-torque magnitude as a function of field direction.
Citation
Physical Review B
Volume
86
Issue
9

Keywords

spin torque, magnetization dynamics, anisotropy, spin transfer, ferromagnetic resonance, oscillator
Created September 4, 2012, Updated November 10, 2018