Magnetic properties of terbium vanadate

Terbium vanadate is a paramagnet with the tetragonal zircon structure (Wyckoff R W 1965 Crystal Structures vol 3 (New York: Interscience)), with space group I4(1)/amd (D-4h(19)). The ground state F-7(6) is split by the crystal field into three doublers and seven singlets. At a temperature of 33 K, a cooperative Jahn-Teller interaction produces a lattice distortion with extensive changes in the electronic energy levels. At the lowest temperatures the ground levels are two singlets, split by nearly 30 GHz. The present paper reports a new determination by means of electron spin resonance of this splitting; this is correlated with earlier measurements, in particular that of the heat capacity below 1 K. Magnetic hyperfine interaction, not previously considered, produces a complex ground state with large enhanced nuclear moments. The antiferromagnetic state below T-N = 0.61 K is attributed to spin-spin interaction between these moments.