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Dielectric anomalies and spiral magnetic order in CoCr2O4

G. Lawes·B. Melot·K. Page·C. Ederer·M. A. Hayward·Th. Proffen·R. Seshadri
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Abstract

We have investigated the structural, magnetic, thermodynamic, and dielectric properties of polycrystalline CoCr$_2$O$_4$, an insulating spinel exhibiting both ferrimagnetic and spiral magnetic structures. Below $T_c$ = 94 K the sample develops long-range ferrimagnetic order, and we attribute a sharp phase transition at $T_N$ $\approx$ 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 CoCr$_2$O$_4$, show a sharp decrease in the dielectric constant at $T_N$, 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.

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G. Lawes, B. Melot, K. Page, C. Ederer, M. A. Hayward, Th. Proffen, R. Seshadri. 2006-03-10. Dielectric anomalies and spiral magnetic order in CoCr2O4. https://doi.org/10.1103/physrevb.74.024413

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