Magnetometry in a diamond anvil cell using nitrogen vacancy centers in a nanodiamond ensemble

The emerging field of optical magnetometry utilizing negative-charged nitrogen vacancy (NV-) centers provides a highly sensitive lab bench technique for spatially resolved physical property measurements. Their implementation in high pressure diamond anvil cell (DAC) environments will become common as other techniques are often limited due to the spatial constraints of the sample chamber. Apparatus and techniques are described here permitting for more general use of magnetic field measurements inside a DAC using continuous wave optical detected magnetic resonance in NV- centers in a layer of nanodiamonds. A microstrip antenna delivers a uniform microwave field to the DAC and is compatible with simple metal gaskets, and the sensor layer of deposited nanodiamonds allows for simple determination of the magnetic field magnitude for B in the 1-100 G range. The ferromagnetic transition in iron at 18 GPa is measured with the apparatus, along with its hysteretic response.