Spectroscopic Study of Magnetic Behavior and Jahn-Teller Distortions in the Even-Electron System TbPO4

The high-resolution optical spectra of TbP${\mathrm{O}}_4$ show that there is antiferromagnetic ordering in the vicinity of 2.25 K, but that there must also be a Jahn-Teller distortion. Evidence that the distortion behavior couples strongly to the magnetic behavior is provided by optical experiments which show that (i) the distortion behavior must occur simultaneously with either magnetic ordering or the application of a large magnetic field and that (ii) the distortion is rotatable by an external magnetic field. It is possible to deduce from the distortion behavior the possible directions for the easy axis. A model is presented to explain the magnetic and distortion behavior. A variety of spectral features, including metamagnetic behavior, are observed but are not fully understood.