High-resolution in-situ magnetic measurement under high pressure has been a challenge. It has limited the progress of research on the Meissner effect of superconductivity and on magnetic phase transition behavior under high pressure. Using the optically detected magnetic resonance (ODMR) technique on diamond nitrogen vacancy (NV) centers has helped in-situ detection of pressure-induced magnetic phase transitions. However, it is not convenient to analyze and interpret the measured ODMR spectra because the NV center has four axial directions and zero-field splitting is temperature dependent.

In this study, the researchers have for the first time realized high-pressure in-situ quantum magnetic detection based on the silicon vacancy (VSi) defects in silicon carbide and solved the problem of high-pressure magnetic detection.

The researchers used ion implantation to generate shallow VSi defects on the surface of a processed silicon carbide anvil cell. VSi defects in silicon carbide have only one axial direction. Due to the special symmetry of silicon carbide's electronic structure, zero-field splitting is insensitive to temperature, thus the problem of temperature variations in high-pressure sensing with NV centers in diamond can be avoided.

The researchers found that the spectrum of VSi defects shifted blue and the zero-field splitting value varied little with pressure (0.31 MHz/GPa)—much less than the slope of diamond NV centers (14.6 MHz/GPa). This is helpful for the measurement and analysis of ODMR spectra under high pressure.

By using ODMR technology on VSi defects, the researchers observed the pressure-induced magnetic phase transition of Nd₂Fe₁₄B magnets at about seven GPa, and measured the critical temperature-pressure phase diagram of the YBa₂Cu₃O_6.6 superconductor.

This technique is of great significance to the field of high-pressure superconductivity and magnetic materials, according to the researchers.

By demonstrating the use of room-temperature spin-defects in silicon carbide as in-situ high pressure sensors, this work opens the door to new studies of quantum materials using Moissanite anvil cells.

This study was supported by the National Natural Science Foundation of China, the Youth Promotion Association of CAS, and the Innovation Foundation of CAS, among others.

Figure 1 (a) and (e) Schematic diagram and illustration of high-pressure in-situ magnetic detection based on shallow VSi defects in MAC. (b) Relationship of zero-field splitting of VSi defects with pressure. (c) Magnetic phase transition detection of Nd2Fe14b materials. (d) Tc-P phase diagram of YBCO superconductor. (Image by LIU Lin)