A short note on spin pumping theory with Landau-Lifshitz-Gilbert equation under quantum fluctuation; necessity for quantization of localized spin

TL;DR

This paper highlights the importance of quantizing localized spins as magnons in spin pumping theory, emphasizing that quantum fluctuations are essential for accurate interpretation of experimental results in spintronics.

Contribution

It points out the necessity of quantizing localized spins in spin pumping models, challenging the classical treatment and proposing a magnon-based perspective for better understanding.

Findings

Quantum fluctuations are central to spin pumping effects.

Localized spins should be treated as magnons, not classical variables.

Precessing ferromagnet acts as a magnon battery.

Abstract

We would like to point out the blind spots of the approach combining the spin pumping theory proposed by Tserkovnyak et al. with the Landau-Lifshitz-Gilbert equation; this method has been widely used for interpreting vast experimental results. The essence of the spin pumping effect is the quantum fluctuation. Thus, localized spin degrees of freedom should be quantized, i.e. be treated as magnons not as classical variables. Consequently, the precessing ferromagnet can be regarded as a magnon battery. This point of view will be useful for further progress of spintronics.