Nanometre-Scale Probing of Spin Waves Using Single-Electron Spins

July 24, 2015

Fig. 1 (a), As a model system to study magnetic excitations, we consider a ferromagnetic microdisc (Ni81Fe19, diameter 6 μm, thickness 30 nm) fabricated on top of a diamond surface. NV centres implanted at ~50 nm below the surface sense the local magnetic fields BM generated by the magnetization M.*

Pushing the frontiers of condensed-matter magnetism requires the development of tools that provide real-space, few-nanometre-scale probing of correlated-electron magnetic excitations under ambient conditions. In an article* in Nature Communications, Harvard Physics postdocs Toeno Van Der Sar and Francesco Casola, Prof. Ronald Walsworth, and Prof. Amir Yacoby present a practical approach to meet this challenge, using magnetometry based on single nitrogen-vacancy centres in diamond. The physicists 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. They map the magnetic-field dependence of spin-wave excitations by detecting the associated local reduction in the disc’s longitudinal magnetization. In addition, they characterize the spin–noise spectrum by nitrogen-vacancy 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.

*See T. van der Sar, F. Casola, R. Walsworth & A.Yacoby, "Nanometre-scale probing of spin waves using single-electron spins," Nature Communications 6: 7886 (07 August 2015) doi:10.1038/ncomms8886