Magnetic resonance imaging of spin-wave transport and interference in a magnetic insulator

Abstract

Spin waves—the elementary excitations of magnetic materials—are prime candidate signal carriers for low-dissipation information processing. Being able to image coherent spin-wave transport is crucial for developing interference-based spin-wave devices. We introduce magnetic resonance imaging of the microwave magnetic stray fields that are generated by spin waves as a new approach for imaging coherent spin-wave transport. We realize this approach using a dense layer of electronic sensor spins in a diamond chip, which combines the ability to detect small magnetic fields with a sensitivity to their polarization. Focusing on a thin-film magnetic insulator, we quantify spin-wave amplitudes, visualize spin-wave dispersion and interference, and demonstrate time-domain measurements of spin-wave packets. We theoretically explain the observed anisotropic spin-wave patterns in terms of chiral spin-wave excitation and stray-field coupling to the sensor spins. Our results pave the way for probing spin waves in atomically thin magnets, even when embedded between opaque materials.

Diamond quantum sensors: from physics to applications on condensed matter research

“…Imaging the transportation of spin waves is crucial for developing spin-wave devices. Bertelli et al [55] introduced a distinct approach, using a layer of NV centre in a diamond chip, to image spin waves in yttrium iron garnet (YIG) thin film in close proximity using phase-sensitive magnetic resonance imaging. The experimental setup was shown in Fig.…”

Diamond-based quantum technologies

“…A recent application studied by one of us focuses on imaging waves in magnets that transport information with little heat production (Fig. 1 e) [5].…”

“…Such efforts are now underway in worldwide collaborations between universities, research centers and industry. [5]). Middle: a diamond nanobeam with an NV positioned onto a nanostructure (image originally published in [2]).…”

“…c) Optical detection of the NV electron spin resonance (ESR) frequency yields the DC magnetic field B. d) Relaxation measurement that quantifies magnetic fields at the gigahertz ESR frequencies. e) Top: an NV-diamond placed onto a sample (image originally published in[5]). Middle: a diamond nanobeam with an NV positioned onto a nanostructure (image originally published in[2]).…”

Frequency multiplication by collective nano-scale spin wave dynamics

“…In this article, we explore the non-linear response of a soft ferromagnet close to zero magnetic field at large driving amplitudes and small frequencies. Spin waves are probed using diamond Nitrogen vacancy (NV) center nanoscale magnetometry [28][29][30][31][32][33][34] and time-resolved magneto optic Kerr microscopy (MOKE) [35][36][37]. In the measurements we indeed find evidence for the expected spin waves precessing at 3/2 of the driving frequency and -very surprisingly -a series of additional spin wave excitations precessing at up to the 60 th harmonic of the pumping frequency.…”