Magnetic-Field Modulation of Polarized Thermal Emissivity in Magnetized Spin Systems: A Bloch-Model Approach

The radiative heat transfer characteristics, particularly emissivity, are critically affected by the temperature-dependent behavior of spin states, which are governed by  their interaction with the magnetic field. Using a Bloch-model-based framework, the study explores how external magnetic fields influence the optical and radiative properties of spin ensembles, revealing pathways for active control of polarized thermal emission at the quantum level. Results from the simplified spin-cloud model reveal that even minor magnetic-field-induced variations in the permeability tensor can lead to pronounced relative changes in emissivity. THz generalized Mueller matrix electron paramagnetic resonance ellipsometry measurements on Fe-doped GaN at cryogenic temperatures validated the theoretical results.[1, 2] Overall, this work establishes a generalized analytical foundation for thermal emissivity characterization that integrates both dielectric permittivity and magnetic permeability tensors, advancing the understanding of magnetically tunable near-field radiative heat transfer and enabling reconfigurable thermal management in quantum photonic systems.

[1] V. Rindert, et.al., Phys. Rev. B 110, 054413 (2024).

[2] V. Rindert et.al., Phys. Rev. Lett. 134, 086703 (2025).