Measurement of Compensated Ferrimagnetism in Terbium Iron Garnet using Neutron Spin Echo Spectroscopy

Rare-earth iron garnets constitute a model system for Néel ferrimagnetism. These materials exhibit temperature-dependent orbital cancellation of the magnetism associated with the electron spins, leaving a dense ensemble of polarized electrons which are of interest as a source for exotic spin-dependent fifth-force searches. We have conducted the first neutron spin echo investigation of the ferrimagnetic state of a terbium iron garnet (Tb₃Fe₅O₁₂) sample. In contrast to measurements of external fields, neutrons can probe the internal state of the ferrimagnet and determine if the cancellation of moments occurs at the unit cell level or is an emergent property as a result of compensation among inhomogeneously-distributed domains. We describe the sample characterization, the apparatus used, as well as preliminary results.