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Current-induced noise and damping in non-uniform ferromagnets

Research paper by Jorn Foros, Arne Brataas, Yaroslav Tserkovnyak, Gerrit E. W. Bauer

Indexed on: 14 Mar '08Published on: 14 Mar '08Published in: Physics - Mesoscopic Systems and Quantum Hall Effect



Abstract

In the presence of spatial variation of the magnetization direction, electric current noise causes a fluctuating spin-transfer torque that increases the fluctuations of the ferromagnetic order parameter. By the fluctuation-dissipation theorem, the equilibrium fluctuations are related to the magnetization damping, which in non-uniform ferromagnets acquires a nonlocal tensor structure. In biased ferromagnets, shot noise can become the dominant contribution to the magnetization noise at low temperatures. Considering spin spirals as a simple example, we show that the current-induced noise and damping is significant.