S=3/2 spin systems on frustrated pyrochlore lattice

The effect of magnetic field on S = 3/2 Heisenberg antiferromagnets on pyrochlore lattice was investigated. Chromium spinels CdCr2O4 and HgCr2O4 exhibit first order field-induced transitions to magnetization plateau states with one-half moment of Cr3+. One-half moment is reasonably understood as formation of collinear three-up and one-down spin configuration for each tetrahedron, which is a building block of pyrochlore lattice. The effect of lattice distortions to stabilize this spin ordering state makes these magnetization plateau phases appear within wide range of magnetic field. It is quite likely that field-induced collinear three-up and one-down state is universal for antiferromagnetic Heisenberg spin systems on pyrochlore lattice, however, such pure spin system seems to be limited to chromium spinel oxides at present. (c) 2006 Elsevier B.V. All rights reserved.