Sensing spin wave excitations by spin defects in few-layer-thick hexagonal boron nitride

Optically active spin defects in wide bandgap semiconductors serve as an advanced local quantum sensor of the microscopic electromagnetic properties of condensed matter systems. Taking advantage of the recent progress on quantum sensing using van der Waals (vdW) materials, here we report direct measurements of spin waves excited in magnetic insulator Y₃Fe₅O₁₂ (YIG) by boron vacancy spin defects contained in a few-layer-thick hexagonal boron nitride nanoflake. We show that the microwave driven ferromagnetic resonance and parametric spin excitations in YIG can be effectively detected by under a broad range of experimental conditions through optically detected magnetic resonance measurements. The off-resonant dipole interaction between YIG magnons and spin defects is mediated by the multi-magnon scattering processes, which may find direct applications in a range of emerging quantum technological innovations. Our results also highlight the opportunities offered by quantum spin defects in layered two-dimensional vdW materials for investigating spin dynamic behaviors in magnetic solid-state matters.