Observation of an intersublattice exchange magnon in CoCr2O4 and analysis of magnetic ordering.

We report on an investigation of optical properties of multiferroic CoCr2O4 at terahertz frequencies in magnetic fields up to 30 T. Below the ferrimagnetic transition (94 K), the terahertz response of CoCr2O4 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 Co2+ and Cr3+ ions), we find the inter-sublattice coupling constant, λ = -(18 ± 1) K, and trace the magnetization for each sublattice as a function of field. We show that the Curie temperature of the Cr3+ sublattice, ϴ2 = (49 ± 2) K, comcides with the temperature range, where anomalies of the dielectric and magnetic properties of CoCr2O4 have been reported in literature. [ABSTRACT FROM AUTHOR]