Pressure Sensor Using a Hybrid Structure of a Magnetostrictive Layer and Nitrogen-Vacancy Centers in Diamond

This study demonstrates imaging of the magnetic response to external pressure using a hybrid structure of magnetostrictive (MS) layers and nitrogen-vacancy ($\mathrm{N}$-V) centers in diamonds. The MS layer facilitates pressure-to-magnetic field conversion, detected by $\mathrm{N}$-V centers. We use hybrid materials comprising in-plane magnetized ${\mathrm{Sm}\mathrm{Fe}}_{2}$ as a MS layer and diamond with $\mathrm{N}$-V centers perfectly aligned in the vertical [111] orientation to effectively detect the pressure-to-magnetic field conversion. The pressure coefficient, defined as the change in the resonant frequency of the optically detected magnetic resonance in response to pressure, is imaged by widefield imaging, while varying the pressure applied to the MS--$\mathrm{N}$-V structure. We observe a pressure-dependent change in the resonant frequency. Through widefield imaging, the pressure coefficients are found to be correlated with the multidomain structure of the MS layer, which must be considered in widefield pressure imaging. The highest pressure coefficient is 8.2 kHz ${\mathrm{kPa}}^{\ensuremath{-}1}$ in a domain---550 times greater than that achieved by a single structure of the $\mathrm{N}$-V center. We propose and discuss the approach of using MS disk arrays consisting of a single domain to improve the sensitivity and controllability and to enable accurate calibration of pressure imaging.