Electromagnetically Induced Absorption in Magnetorheological Microcavities Enables Precise Hysteresis Sensing

Electromagnetically induced absorption (EIA) enables subnatural spectral features and enhanced light–matter interaction, yet its implementation in integrated photonics has been hampered by the challenge of maintaining coherent phase control in high-Q microcavities. Here, we report a magnetically tunable photonic platform in which whispering-gallery microspheres are functionalized with magnetorheological elastomers (MrEs), providing anisotropic permeability and reconfigurable optical responses while preserving ultrahigh quality factors (Q >107). This hybrid architecture supports the first demonstration of magnetically controlled photonic EIA, exhibiting tunable Fano-like asymmetries, Boltzmann-distributed spectral detuning, and a record magnetic sensitivity of −598.02 MHz/mT─exceeding prior cavity-based magnetometers by over an order of magnitude. Moreover, the EIA detuning traces reproduce the hysteresis behavior of the nanoparticle–elastomer composite, enabling direct optical quantification of magnetic squareness ratios (Sr >0.7) with submillitesla resolution. By combining coherent photonic interference with soft-matter magnetism, this work establishes magnetically reconfigurable EIA as a new route for cavity-based dispersion engineering, with implications for quantum metrology, precision spectroscopy, and magneto-optical photonic devices.