Magnetically critically enhanced hybrid hBN quantum thermometer

The boron vacancy (VB−) defects in hexagonal boron nitride (hBN) have shown significant potential in various quantum sensing due to their unique properties. Particularly, the VB− defects are particularly promising for nanoscale quantum thermometers owing to their high temperature dependent zero-field splitting parameter D (−0.8 MHz/K). In order to increase the sensitivity, one method is to increase the slope of the temperature dependent D. In this work, we realize two types of the magnetically critically enhanced hybrid hBN quantum thermometer over a wide temperature range. The slope coefficient dD/dT reached −3.51 and −3.61 MHz/K in the corresponding magnetically critically temperature range for the Cu1Ni3 alloy/gadolinium metal and hBN Hybrid system, with corresponding sensitivities reaching 0.3 and 0.43 K/Hz, respectively. Both the values are about more than three times larger than the bare value, which demonstrates the magnetically critically enhanced effect. This enhancement is attributed to the susceptibility of the magnetic material near its critical temperature. Finally, we compare the spin relaxation rate of the (VB−) in bare and Cu1Ni3 hybrid hBN, and the spin relaxation rate revealed a pronounced peak near the Cu1Ni3 alloy Curie temperature (approximately 323 K). The experiments give the basis for constructing a novel hybrid hBN quantum thermometer, combined with its device compatibility, which could be widely used in practical environments.