Lawes, G., Melot, B., Page, K., Ederer, C., Hayward, M.A., Proffen, Th., Seshadri, R. 'Dielectric anomalies and spiral magnetic order in CoCr2 O4' in Physical Review B - Condensed Matter and Materials Physics, 74, (2), 2006, no. 024413
Physical Review B - Condensed Matter and Materials Physics 74 2
We have investigated the structural, magnetic, thermodynamic, and dielectric properties of polycrystalline CoCr2 O4, 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 TS 27 K to the onset of long-range spiral magnetic order. Neutron measurements confirm that the structure remains cubic at 80 K and at 11 K; the magnetic ordering by 11 K is seen to be rather complex. Density functional theory supports the view of a ferrimagnetic semiconductor with magnetic interactions consistent with noncollinear ordering. Capacitance measurements on CoCr2 O4 show a sharp decrease in the dielectric constant at TS, but also an anomaly showing thermal hysteresis falling between approximately T=50 and 57 K. We tentatively attribute the appearance of this higher-temperature dielectric anomaly to the development of short-range spiral magnetic order, and discuss these results in the context of utilizing dielectric spectroscopy to investigate noncollinear short-range magnetic structures.
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