Compensated Ferrimagnetism Measurements and Exotic Polarized Neutron-Polarized Electron Interaction Searches in Terbium Iron Garnets*

Rare earth iron garnets are known to be ferrimagnetic. In these materials, the magnetism associated with the electron spins undergoes a temperature-dependent orbital cancellation. This provides a dense ensemble of polarized electrons in an environment with no net magnetization and an opportunity to search for exotic interactions if the cancellation occurs at the unit cell level. We have studied the ferrimagnetic state of terbium iron garnet (Tb3Fe5O12) with neutron spin echo spectroscopy and neutron imaging to determine if the cancellation of magnetic moments occurs at the unit cell level or is the result of inhomogeneously distributed domains. The same techniques can be used to conduct searches for beyond-the-Standard Model spin-dependent neutron-electron interactions. We discuss the experimental apparatuses and results.