Δ E effect-enabled optomechanical magnetometers for DC magnetic field detection

The detection of direct current (DC) magnetic fields is essential for applications including space exploration, marine monitoring, and seismic study. In this work, we demonstrate a cavity optomechanical magnetometer for DC magnetic field sensing, which integrates a magnetostrictive FeGaB thin film on a SiO2 microdisk resonator. By leveraging the ΔE effect in FeGaB, where an external magnetic field modulates the material's Young's modulus, the magnetometer achieves a minimum detectable DC magnetic field of 598 pT at a bias field of 3.1 mT. This sensitivity represents an improvement of nearly two orders of magnitude over previous optical microcavity-based devices. Furthermore, we experimentally demonstrate its capability to detect time-varying DC magnetic fields. The device operates at room temperature and offers advantages in compactness and mass-producibility, indicating potential for military surveillance, geological surveys, and pre-seismic phenomena study.