Electrical and magnetic properties of double perovskite Y2-xCaxCoMnO6 (x = 0.1, 0.2, 0.5)

Abstract

The crystal structure, electronic, magnetic, and transport properties of the hole substituted (Ca²⁺) and partially B-site disordered double perovskite Y_2-xCa_xCoMnO₆ system are studied. At room temperature, the samples demonstrated a monoclinic perovskite structure with a space group P2₁/n which was confirmed by Rietveld refinement of X-ray diffraction data. Ultra-violet visible analysis of these samples shows a direct band gap including gap energy near about 1.50 eV. X-ray photoemission spectroscopy measurement shows that component Co and Mn ions exist in a mixed state (Co³⁺, Co²⁺, Mn³⁺, and Mn⁴⁺). All samples exhibit semiconducting/insulating, and electrical conduction can be explained by Mott’s 3-D variable range hopping and small polaron hopping fitting. The magnetization numerical value decreases observed with increases in Ca concentration appears to be caused by increases in antiferromagnetic (AFM) phases. The double perovskite Y_1.9Ca_0.1CoMnO₆ and Y_1.8Ca_0.2CoMnO₆ show ferromagnetic transition at transition temperatures T_c~ 70 K and T_c~ 68 K, respectively. The analysis of the samples’ zero fields cooled DC magnetic susceptibility as a function of temperature reveals Griffiths-like singularity features that arise as the concentration of Ca increases in the parent system. The Griffith-like phase exists in the sample Y-site with Ca-substitution is independent of the structural disorder caused by the John–Teller active Mn³⁺ions in sample \({\text{Y}}_{1.5} {\text{Ca}}_{0.5}\)CoMnO₆. Field-dependent magnetization shows meta-magnetic behavior at low-temperature regions in Y_1.9Ca_0.1CoMnO₆ and Y_1.8Ca_0.2CoMnO₆. As the concentration of Ca increased from Y_1.8Ca_0.2CoMnO₆ to Y_1.5Ca_0.5CoMnO₆ meta-magnetic behavior disappeared.