Reentrant spin glass behavior and magnetodielectric coupling of an Ir-based double perovskite compound, La₂CoIrO₆

The structural, magnetic, electrical and dielectric properties of an Ir-based double perovskite compound, La₂CoIrO₆, have been investigated. The sample undergoes a paramagnetic-ferromagnetic transition at T_C, followed by a reentrant spin-glass transition at lower temperatures. The reentrant spin glass state in La₂CoIrO₆ is associated with the competitions of the antiferromagnetic coupling between Ir⁴⁺ and Co²⁺ ions and the ferromagnetic clusters. La₂CoIrO₆ shows a semiconducting transport behavior in the temperature range 65 to 360 K and the transport behavior can be well described by the three-dimensional Mott variable range hopping conduction mechanism. Moreover, a strong frequency dependence of dielectric constant behavior for La₂CoIrO₆ is observed and the dielectric relaxation can be ascribed to the electron hopping between different transition metal ions. In addition, the isothermal magnetic field dependent dielectric constant measurements show that a clear magnetodielectric coupling effect exists in La₂CoIrO₆ at low temperatures.