Abstract. The structural and magnetic properties of the geometrically frustrated spinel system CdV₂O₄ with V³⁺ (S = 1), whose lattice constant and oxygen u-parameter differ significantly from those of isomorphous MgV₂O₄ and ZnV₂O₄, have been explored by means of x-ray diffraction and through measurements of the magnetization and nuclear magnetic resonance. CdV₂O₄ undergoes a cubic–tetragonal structural transition with c_t/a_t = 0.990 as well as a magnetic transition with a jump of the susceptibility at T_c1 = 97 K. Another magnetic anomaly appears at T_c2 = 35 K which may be a transition to the antiferromagnetic state. The analysis in terms of the high-temperature series expansion of up to eighth order precisely indicates the nearest-neighbour exchange-coupling constant for the cubic phase to be J = 44 K. In the vanadium spinel with S = 1, the spin-singlet V₄-tetramer model with the exchange coupling J_tet inside V₄, where J_tet = 2J, is applicable at temperatures above T J_tet: for CdV₂O₄ with J_tet ≤T_c1, all of the susceptibility data for the cubic phase are explained using that model, while for MgV₂O₄ and ZnV₂O₄ with J_tet ≥T_c1, it is difficult to account for the data for between J_tet and T_c1. In this sense, the present bound state may be regarded as pseudotetramers.

Print publication: Issue 28 (22 July 2002)
Received 8 May 2002
Published 5 July 2002