Enhanced dielectric and magnetic properties of magnetodielectric La2−xPrxCoMnO6 for spintronic applications

Abstract

La2−xPrxCoMnO6 (x = 0.5, 1.0, 1.5 and 2.0) double perovskites were prepared via sol gel method. X-ray diffraction peak profile inveterate the nonexistence of impurity phases in the prepared system. Rietveld refinement suggested that ordered monoclinic (P21/n) phase exist along with disordered orthorhombic (Pbnm) and rhombohedral (R3c) structural phases. A decrease in unit cell volume and lattice parameters is observed with increase in Pr content which is in agreement with the difference in ionic radii of La and Pr ions. Morphological and compositional study using FESEM with EDX suggested that grain size lies in micrometer range and signifies the purity of developed samples. Dielectric constant as well as tangent loss exhibit dispersive behavior at lower frequencies and higher temperatures. The strong effect of bond angle, anti-site disorder and grain size is observed on dielectric properties. Due to large bond angle and large antisite disorder, LPCMO2 exhibited largest value of dielectric constant among all developed compositions. Cole-Cole plots proposed a non-Debye type relaxation and indicated NTCR (negative temperature coefficient of resistance) behavior for the synthesized compositions. Ac conductivity showed increasing tendency with rise in both frequency as well as temperature. Increase in dc conductivity with temperature proposed semiconducting behavior of prepared samples that can be explained on the basis of Thermal activation (TA) and Variable range hopping (VRH) models. The saturation magnetization (Ms) showed a strong correlation with bond angle, tilting of CoO6/MnO6 octahedra and grain size i.e. LPCMO2 is having largest Ms whereas lowest Ms is exhibited by LPCMO3 which may be due to variation in exchange interaction which strictly depends on bond angle and tilting of MO6 octahedra. Enhanced magnetic properties make these materials useful for spintronic devices and magnetic storage. Dielectric and magnetic properties of the prepared samples depend strongly on ˂Co-O-Mn˃ bond angle and have same variation tendency with Pr substitution which indicates coupling between these properties.