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

Spin waves in magnetic insulators can transport information without the dissipation caused by moving charges, and could therefore play a major role in future information processing technology. Using electron spins in diamond, we introduce a phase-sensitive detection scheme to image spin waves via their magnetic field, which we use to quantify the spin-wave precession amplitude in YIG and image spin-wave interference and caustics. The observed patterns are well reproduced by a model based on the chiral spin-wave excitation and coupling to the sensor spins. Detecting spin-waves via their magnetic field allows imaging through optically opaque materials, paving the way for studies of multilayers and top-gated systems, and to study the interaction of spin waves and electric currents. The sensitivity of our technique, which can reach a nanometric spatial resolution when implemented in a scanning geometry, allows to detect spin waves in ultrathin magnetic films, down to the monolayer limit.