Constraints on Exotic Spin-Dependent Interactions in Ferrimagnetic Targets at Compensation Temperature

Rare-earth iron garnets are a well-known example of ferrimagnetic materials which exhibit a temperature dependent cancellation of magnetism. This ideally results in a dense ensemble of polarized electrons with zero magnetization [1]. The Neutron Spin Rotation Collaboration has applied slow neutron polarimetry and neutron imaging techniques to polycrystalline terbium iron garnet Tb₃Fe₅O₁₂ held at its compensation temperature for sensitive measurements of exotic spin-dependent neutron-electron interactions. We present new constraints on the couplings g_Ag_A, g_Pg_P, g_Vg_V for exotic electron-neutron interactions derived from the analysis of two experiments conducted at the HFIR CG-1D neutron imaging beamline at ORNL. These findings provide new sensitivity to long-range, spin-dependent forces and contribute to the broader search for new physics beyond the Standard Model.

[1] C. D. Hughes et al., Journal of Magnetism and Magnetic Materials 629, 173273 (2025).