Quantum magnetization fluctuations via spin shot noise

TL;DR

This paper introduces a quantum theory explaining magnetization fluctuations in spin valves as caused by spin shot noise, showing asymmetrical increases with bias and quantum effects at higher temperatures, aligning with recent experiments.

Contribution

It presents a quantum model attributing magnetization fluctuations to spin shot noise, challenging semiclassical predictions and explaining experimental observations.

Findings

Fluctuations increase asymmetrically with bias.

Quantum effects influence fluctuations at higher temperatures.

Results align with recent experimental data.

Abstract

Recent measurements in current-driven spin valves demonstrate magnetization fluctuations that deviate from semiclassical predictions. We posit that the origin of this deviation is spin shot noise. On this basis, our theory predicts that magnetization fluctuations asymmetrically increase in biased junctions irrespective of the current direction. At low temperatures, the fluctuations are proportional to the bias, but at different rates for opposite current directions. Quantum effects control fluctuations even at higher temperatures. Our results are in semiquantitative agreement with recent experiments and are in contradiction to semiclassical theories of spin-transfer torque.