Nanometre-scale probing of spin waves using single electron spins

TLDR

Correlated‑electron systems host diverse magnetic excitations, yet no established technique enables real‑space, few‑nanometre‑scale probing of these excitations under ambient conditions. The study aims to probe nanometre‑scale magnetic excitations to advance spintronic devices, presenting a solution via single‑NV‑center magnetometry. The authors use single‑NV‑center magnetometry to map spin‑wave magnetic fields and detect local reductions in longitudinal magnetization of a ferromagnetic microdisc. They demonstrate local, quantitative, phase‑sensitive detection of spin‑wave magnetic fields at ~50 nm from a ferromagnetic microdisc, characterize the spin‑noise spectrum in agreement with analytical models, and show that these modalities enable imaging of excitations in diverse magnetic systems such as ferromagnets, antiferromagnets, skyrmions, quantum magnets, and spin ice.

Abstract

Correlated-electron systems support a wealth of magnetic excitations, ranging from conventional spin waves to exotic fractional excitations in low-dimensional or geometrically-frustrated spin systems. Probing such excitations on nanometre length scales is essential for unravelling the underlying physics and developing new spintronic nanodevices. However, no established technique provides real-space, few-nanometre-scale probing of correlated-electron magnetic excitations under ambient conditions. Here we present a solution to this problem using magnetometry based on single nitrogen-vacancy (NV) centres in diamond. We focus on spin-wave excitations in a ferromagnetic microdisc, and demonstrate local, quantitative, and phase-sensitive detection of the spin-wave magnetic field at ~50 nm from the disc. We map the magnetic-field dependence of spin-wave excitations by detecting the associated local reduction in the disc's longitudinal magnetization. In addition, we characterize the spin-noise spectrum by NV-spin relaxometry, finding excellent agreement with a general analytical description of the stray fields produced by spin-spin correlations in a 2D magnetic system. These complementary measurement modalities pave the way towards imaging the local excitations of systems such as ferromagnets and antiferromagnets, skyrmions, atomically assembled quantum magnets, and spin ice.