With the help of density functional theory calculations, we explored the recently synthesized double perovskite material Ca2CrOsO6 and found it to be a ferrimagnetic insulator with a band gap of ∼0.6 eV.
We investigate the electronic and magnetic properties of Ca2CrIrO6 and Ca2FeIrO6 by means of density functional theory. These materials belong to a family of recently synthesized Ca2CrOsO6 whose properties show possible applications in a room temperature regime. Upon replacement of Os by Ir in Ca2CrOsO6, we found the system to exhibit a stable ferrimagnetic configuration with a bandgap of ∼0.25 eV and an effective magnetic moment of ∼2.58μB per unit cell. Furthermore, when chemical doping is considered by replacing Cr with Fe and Os with Ir, the material retains the insulating state but with a reduced bandgap of 0.13 eV and large increment in the effective magnetic moment of ∼6.68μB per unit cell. These observed behaviors are noted to be the consequence of the cooperative effect of spin–orbit coupling; Coulomb correlations from Cr-3d, Fe-3d, and Ir-5d electrons; and the crystal field effect of the materials. These calculations suggest that by chemical tuning, one can manipulate the bandgap and their effective magnetic moment, which may help in material fabrication for device applications. To check further the suitability and applicability of Ca2CrIrO6 and Ca2FeIrO6 at higher temperatures, we estimate the Curie temperature (TC) by calculating the spin–exchange coupling. We found that our findings are in a valid TC trend similar to other perovskites. Our findings are expected to be useful in experimental synthesis and transport measurement for potential applications in modern technological devices.
The perovskite TbFe 0.5 Cr 0.5 O 3 shows two anomalies in its magnetic susceptibility at T N = 257 K and T SR = 190 K which are, respectively, the antiferromagnetic and spin-reorientation transition that occur in the Fe/Cr sublattice. Magnetic susceptibility of this compound reveals canonical signatures of a Griffiths-like phase: a negative deviation from the ideal Curie-Weiss law and in less-than-unity power-law susceptibility exponents. Neutron-diffraction data analysis confirms two spin-reorientation transitions in this compound. The first one from 2 (C x , G y , F z ) to 4 (A x , F y , G z ) occurs at T N = 257 K and a second one from 4 (A x , F y , G z ) to 2 (C x , G y , F z ) at T SR = 190 K in the Pnma space-group setting. The 2 (C x , G y , F z ) structure is stable down to 7.7 K, leading to an ordered moment of 3.34(1) μ B /Fe 3+ (Cr 3+ ). In addition to the long-range magnetic order, experimental indication of diffuse magnetism is observed in neutron-diffraction data at 7.7 K. Tb develops a ferromagnetic component along the z axis at 20 K. Thermal conductivity and spin-phonon coupling of TbFe 0.5 Cr 0.5 O 3 studied through Raman spectroscopy are also presented in the paper. The magnetic anomalies at T N and T SR do not appear in the thermal conductivity of TbFe 0.5 Cr 0.5 O 3 , which appears to be robust up to 9 T. On the other hand, they are revealed in the temperature dependence of full-width-at-half-maximum curves derived from Raman intensities. An antiferromagnetic structure with ↑↓↑↓ arrangement of Fe/Cr spins is found as the ground state through first-principles energy calculations, supporting the experimentally determined magnetic structure at 7.7 K. The spin-resolved total and partial density of states show that TbFe 0.5 Cr 0.5 O 3 is insulating with a band gap of ∼0.12 (2.4) eV within GGA (GGA+U ) functionals.
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