Radiofrequency studies of TmVO 4

Abstract

The electronic ground state of Tm³⁺, ³H₆, is a non-Kramers doublet which, below a critical temperature T_D, is split by a cooperative Jahn-Teller distortion. Radiofrequency measurements of the susceptibility have established that (a) T_D = 2.156(5) K; (b) most of the magnetic specific heat above T_D comes from random splittings of the doublet, ascribed to local strains; (c) the critical field B_c needed to counteract the distortion below T_D follows very closely the molecular field theory for spin ½. Measurements of the ⁵¹V n.m.r. spectrum above T_D give values for the internal field at both V and Tm sites; interactions between Tm ions are predominantly dipolar. Below T_D, both the ⁵¹V spectrum and the enhanced ¹⁶⁹Tm spectrum show anisotropy in the (001) plane, whose principal axes, [110] and [110], confirm that these are the principal axes of the Jahn-Teller distortion. The temperature at which the enhanced ¹⁶⁹Tm nuclear moments should enter an ordered phase is estimated as 0.2-0.3mK.