Pressure-induced magnetic phase transitions are attracting interest as a means to detect superconducting behaviour at high pressures in diamond anvil cells, but determining the local magnetic properties of samples is a challenge due to the small volumes of sample chambers. Optically detected magnetic resonance of nitrogen vacancy centres in diamond has recently been used for the in situ detection of pressure-induced phase transitions. However, owing to their four orientation axes and temperature-dependent zero-field splitting, interpreting these optically detected magnetic resonance spectra remains challenging. Here we study the optical and spin properties of implanted silicon vacancy defects in 4H-silicon carbide that exhibit single-axis and temperature-independent zero-field splitting. Using this technique, we observe the magnetic phase transition of Nd₂Fe₁₄B at about 7 GPa and map the critical temperature–pressure phase diagram of the superconductor YBa₂Cu₃O_6.6. These results highlight the potential of silicon vacancy-based quantum sensors for in situ magnetic detection at high pressures.

压力诱导的磁相变作为检测金刚石砧座中高压下超导行为的一种手段引起了人们的兴趣，但由于样品室体积小，确定样品的局部磁性是一项挑战。金刚石中氮空位中心的光学检测磁共振最近已用于压力诱导相变的原位检测。然而，由于它们的四个取向轴和与温度相关的零场分裂，解释这些光学检测到的磁共振光谱仍然具有挑战性。在这里，我们研究了 4H-碳化硅中注入的硅空位缺陷的光学和自旋特性，这些缺陷表现出单轴和与温度无关的零场分裂。使用这种技术，₂ Fe ₁₄ B 在大约 7 GPa 并绘制超导体 YBa ₂ Cu ₃ O _6.6的临界温度-压力相图。这些结果突出了基于硅空位的量子传感器在高压下进行原位磁检测的潜力。