Symmetry Breaking in a Frustrated Heisenberg Spin System, ZnCr₂O₄: I. Magnetic Measurements

Abstract

Magnetization was measured for a ZnCr 2 O 4 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 11] or of 60 kOe along the [0 "1 11] 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 À2 J/g or 10 À3 cm À1 /Cr ion, by magnetization curves. It was suggested that the magnetic symmetry of the ground state is lower than monoclinic.

Magnetic ground state of ZnCr2 O4 : Effect of disorder due to size reduction

“…For ZCO-B, M(T ) curve shows a sharp drop with decreasing temperature near T N = 13 K signifying the onset of AFM transition. ZFCH data show a hump like feature around 45 K which is a signature of short range AFM correlations above T N as reported earlier[14,17]. The M(T ) data of ZCO-N show considerably different behavior than ZCO-B.…”

“…ZCO undergoes a long range antiferromagnetic (AFM) ordering near T N = 13 K along with a structural transition from a high-T cubic to a low-T tetragonal phase [15,16]. Signature of short range AFM correlation above T N was reported in earlier investigation [14,17]. ZCO also shows magneto-dielectric coupling below T N [14].…”