Magnetic Criticality Enhanced Hybrid Nanodiamond Thermometer under Ambient Conditions

Nitrogen-vacancy (NV) centers in diamond are attractive as quantum sensors owing to their superb coherence under ambient conditions. However, the NV center spin resonances are relatively insensitive to some important parameters such as temperature and pressure. Here we design and experimentally demonstrate a hybrid nanothermometer composed of NV centers and a magnetic nanoparticle (MNP), in which the temperature sensitivity is enhanced by the critical magnetization of the MNP near the ferromagnetic-paramagnetic transition temperature. The temperature susceptibility of the NV center spin resonance reaches 14 MHz/K, nearly 200 times larger than that of bare NV centers. The sensitivity of a hybrid nanothermometer composed of a Cu1-xNix MNP and a nanodiamond is measured to be 11 mK root Hz under ambient conditions. The working range of the hybrid thermometer can be designed from cryogenic temperature to about 600 K by tuning the chemical composition of the Cu1-xNix MNP. We demonstrate in situ detection of the magnetic phase transition of a single magnetic nanoparticle using the hybrid nanothermometer. This hybrid nanothermometer provides a novel approach to studying a broad range of thermal processes at nanoscales such as nanoplasmonics, heat-stimulated subcellular processes, and thermodynamics of nanosystems.