Symmetry breaking in a frustrated Heisenberg spin system, ZnCr2O4:: I.: Magnetic measurements

Magnetization was measured for a ZnCr2O4 single crystal as a function of field direction, in a magnetic field range of 0.5-50 kOe, mainly at 5 K. To examine the effect of magnetic domain distribution, the crystal was cooled through T-N, 12.2 K, with or without pressure along the [001] axis and a magnetic field of 50 kOe along the [1 (1) over bar1] or of 60 kOe along the [0 (1) over bar1] axis. No spontaneous magnetization was detected within the accuracy of the experiment. Above 3 kOe, the anisotropy of magnetic susceptibility decreases with increasing magnetic field, to approximately two or three orders of magnitude smaller at 30 kOe. This finding indicates that the ground state lies near the magnetically isotropic (symmetric) state but is slightly distorted. The energy difference between the symmetric state and the ground state was estimated to be on the order of 10(-2) J/g or 10(-3) cm(-1)/Cr ion, by magnetization curves. It was suggested that the magnetic symmetry of the ground state is lower than monoclinic.