Measurement of the thulium ion spin Hamiltonian in an yttrium gallium garnet host crystal

This is the authors' abstract. We don't add key points for this paper.

The magnetic properties of crystals doped with rare-earth ions have long been studied for their long coherence times and applications in signal processing. Here, the authors measure a complete tensor description of the hyperfine structure for a pair of optically addressable levels belonging to the Tm³⁺-ion defects within the host material. Certain orientations of interest stand out, such as some that realize optical clock transitions; they are shown to have an invariant response to fluctuations in the local magnetic environment.