Effect of rare earth site substitution on magnetic and transport properties of Ln2CoMnO6 (Ln = La, Sm and Gd) double perovskites

The influence of rare earth site substitution on structural, transport and magnetic characteristics of poly-crystalline Ln(2)CoMnO(6) (Ln = La, Sm and Gd) has been systematically investigated in details. The room temperature X-ray diffraction data confirm the monoclinic crystal structure of the samples, having P2(1)/n space group. The magnetic study reveals that the ferromagnetic transition temperature (T-C1 similar to 233.2 K) of La2CoMnO6 decreases very fast due to a decrease of ionic radii in Ln site and T-C2 (similar to 150 K) disappears in the Gd2CoMnO6 system due to the presence of only Co2+ and Mn4+ ion pair. The field dependent magnetization data at 5 K exhibit antiferromagnetic ordering induced in the Sm2CoMnO6 and Gd2CoMnO6 systems due to structural distortion and 4f-3d negative magnetic interactions. The temperature dependent resistivity data of La2CoMnO6 display semiconductor like behavior in a temperature range of 150-300 K and this behavior has been best described by the variable range hopping conduction mechanism. On the other hand, the resistivity of Sm and Gd based samples follows variable range hopping model in the temperature range of 200-300 K. Large magnetoresistance of similar to-26.35% has been observed at 160 K at a magnetic field of 60 kOe in La2CoMnO6 and it decreases to -8.28% for Sm2CoMnO6, and -1.01% for Gd2CoMnO6 as ionic radii decrease at the Ln site. (C) 2018 Elsevier B.V. All rights reserved.