Probing ac & dc magnetic properties of van der Waals materials with a programmable quantum sensor

The dc magnetism of atomically-thin van der Waals (vdW) magnets has been successfully characterized by multiple, although sophisticated, techniques. However exploration of the dynamic regime of vdW magnets, which is crucial for understanding the magnetic phase transition and interactions, has been experimentally elusive. We have recently demonstrated that the nitrogen-vacancy (NV) center in diamond is a quantitative, programmable probe for both the ac and dc magnetic properties of vdW materials. Through quantum control over the NV center's coherent spin precession, we realize sensitive ac susceptometry of exfoliated vdW magnets over a broad phase space in temperature, external dc field, and ac excitation frequency. Our measurements provide detailed information about the domain wall dynamics and ferromagnetic phase transition of few layer CrBr_3. Our magnetometry platform thus opens a generalizable avenue for probing magnetic excitations in wide-ranging 2D materials.