Spin-Noise and Damping in Individual Metallic Ferromagnetic Nanoparticles

TL;DR

This paper presents a novel charge sensing technique to observe magnetization dynamics in single Ni nanoparticles at millikelvin temperatures, revealing long magnetic damping times and nonequilibrium effects.

Contribution

It introduces a sensitive charge sensing method to study magnetization motion in individual metallic nanoparticles, providing new insights into damping and noise at the nanoscale.

Findings

Magnetic damping time peaks at around 10 ms with magnetic field.

Charge noise correlates with magnetization dynamics in real time.

Nonequilibrium magnetization effects are observed via electron tunneling.

Abstract

We introduce a highly sensitive and relatively simple technique to observe magnetization motion in single Ni nanoparticles, based on charge sensing by electron tunneling at millikelvin temperature. Sequential electron tunneling via the nanoparticle drives nonequilibrium magnetization dynamics, which induces an effective charge noise that we measure in real time. In the free spin diffusion regime, where the electrons and magnetization are in detailed balance, we observe that magnetic damping time exhibits a peak with the magnetic field, with a record long damping time of $\simeq 10$~ms.