  Recently we have demonstrated AC magnetic field sensing scheme using a simple
continuous-wave optically detected magnetic resonance of nitrogen-vacancy
centers in diamond [Appl. Phys. Lett. 113, 082405 (2018)]. This scheme is based
on electronic spin double resonance excited by continuous microwaves and
radio-frequency (RF) fields. Here we measured and analyzed the double resonance
spectra and magnetic field sensitivity for various frequencies of microwaves
and RF fields. As a result, we observed a clear anticrossing of RF-dressed
electronic spin states in the spectra and estimated the bandwidth to be
approximately 5 MHz at the center frequency of 9.9 MHz.
