We have investigated the structural, magnetic, thermodynamic, and dielectric properties of polycrystalline CoCr2O4, an insulating spinel exhibiting both ferrimagnetic and spiral magnetic structures. Below Tc = 94 K the sample develops long-range ferrimagnetic order, and we attribute a sharp phase transition at TN≈ 25 K with the onset of long-range spiral magnetic order. Neutron measurements confirm that while the structure remains cubic at 80 K and at 11 K; there is complex magnetic ordering by 11 K. Density functional theory supports the view of a ferrimagnetic semiconductor with magnetic interactions consistent with non-collinear ordering. Capacitance measurements on CoCr2O4, show a sharp decrease in the dielectric constant at TN, but also an anomaly showing thermal hysteresis falling between approximately T = 50 K and T = 57 K. We tentatively attribute the appearance of this higher temperature dielectric anomaly to the development of \textit{short-range} spiral magnetic order, and discuss these results in the context of utilizing dielectric spectroscopy to investigate non-collinear short-range magnetic structures.
@article{arxiv.cond-mat/0603307,
title = {Dielectric anomalies and spiral magnetic order in CoCr2O4},
author = {G. Lawes and B. Melot and K. Page and C. Ederer and M. A. Hayward and Th. Proffen and R. Seshadri},
journal= {arXiv preprint arXiv:cond-mat/0603307},
year = {2007}
}