Nanoscale Detection of Magnon Excitations with Variable Wavevectors Through a Quantum Spin Sensor

Control and manipulation of pure spin currents in magnetic insulators has been a central focus of modern spintronic research. Building on the transformative nitrogen vacancy (NV) based quantum sensing platform, we have achieved local detection of a range of spin wave modes in magnetic insulator Y3Fe5O12 thin films over a 100-nanometer length scale. Through the multi-magnon scattering process, the excited spin waves generate fluctuating magnetic fields at the NV electron spin resonance frequencies, accelerating the relaxation of the NV spin. By measuring the variation of the emitted photoluminescence of the NV center, the detailed information of the magnon modes can be optically accessed, providing a unique window to reveal the local magnetic properties of the studied materials. Our findings highlight the significant opportunities offered by NV spin quantum sensors in exploring nanoscale spin dynamics of emergent spintronic systems.