D. Kamenskyi, H. Engelkamp, T. Fischer, M. Uhlarz, J. Wosnitza, B. P. Gorshunov, G. A. Komandin, A. S. Prokhorov, M. Dressel, A. A. Bush, V. I. Torgashev, A. V. Pronin
We report on an investigation of optical properties of multiferroic CoCr$_{2}$O$_{4}$ at terahertz frequencies in magnetic fields up to 30 T. Below the ferrimagnetic transition (94 K), the terahertz response of CoCr$_{2}$O$_{4}$ is dominated by a magnon mode, which shows a steep magnetic-field dependence. We ascribe this mode to an exchange resonance between two magnetic sublattices with different $g$-factors. In the framework of a simple two-sublattice model (the sublattices are formed by Co$^{2+}$ and Cr$^{3+}$ ions), we find the inter-sublattice coupling constant, $\lambda = - (18 \pm 1)$ K, and trace the magnetization for each sublattice as a function of field. We show that the Curie temperature of the Cr$^{3+}$ sublattice, $\Theta_{2}$ = $(49 \pm 2)$ K, coincides with the temperature range, where anomalies of the dielectric and magnetic properties of CoCr$_{2}$O$_{4}$ have been reported in literature.
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http://arxiv.org/abs/1304.6525
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