Spin-glass behavior in an antiferromagnetic frustrated spinel: ZnCr1.6Ga0.4O4

Abstract

A study of magnetic properties in the insulating spinel ${\mathrm{ZnCr}}_{1.6}$ ${\mathrm{Ga}}_{0.4}$ ${\mathrm{O}}_4$ (chromium ions in octahedral sites) has been made by carrying out low-field dc- and ac-susceptibility measurements as well as neutron diffraction, Mössbauer, and EPR experiments, which all give evidence of spin-glass-like behavior. The topological frustration, connected with the high ground-state degeneracy of the antiferromagnetic spinel octahedral sublattice, is the origin of the spin-glass ordering. Strong nearest-neighbor antiferromagnetic interactions are dominant in the system, leading to short-range magnetic order which appears at temperatures much higher than the freezing temperature defined by the acsusceptibility cusp [$T(\nu =17\mathrm{} \mathrm{Hz})=2.50\mathrm{}$ K is frequency dependent]. The thermoremanent magnetization does not vanish at $T_f$, suggesting the existence of uncompensated clusters blocked above $T_f$. A paramagnetic behavior is observed below $T=1\mathrm{}$ K, providing evidence for the presence of unfrozen spins below $T_f$ (entropic clusters).