The magnetic fields generated by spins and currents provide a unique window into condensed-matter physics. Proposed only a decade ago, magnetometry based on the electron spin of the nitrogen-vacancy (NV) defect in diamond is emerging as a platform that is excellently suited for probing condensed-matter systems: it is operable from cryogenic to above room temperature, has a dynamic range of DC to GHz, and allows sensor-sample distances down to a few nanometers. As such, NV magnetometry provides nanoscale access to the physics of systems ranging from paramagnetic spin baths to correlated-spin materials. In this talk, I will introduce the basic concepts of NV magnetometry, highlight milestone results such as room-temperature imaging of a single electron spin, and describe recent developments in applying NV magnetometry to study spin dynamics in ferromagnets [1,2].
 - T. van der Sar*, F. Casola*, et al., Nanometre-scale probing of spin waves using single electron spins. Nat. Commun. 6, 7886 (2015).
 - C. Du*, T. van der Sar*, T. Zhou*, et al., Control and local measurement of the spin chemical potential in a magnetic insulator. Science 357, 196 (2017).