On the magnetotransport properties and Griffith phase in (La,Gd)1.4 (Ca,Sr)1.6 Mn2 O7 the double layered manganites

Abstract

The bilayered manganite with formula \({ \text{L}\text{a}}_{1.2}{\text{G}\text{d}}_{0.2}{\text{C}\text{a}}_{1.2}{\text{S}\text{r}}_{0.4}{\text{M}\text{n}}_{2}{\text{O}}_{7}\)has been synthesized by the solid state reaction route with the aim of studying its structural, microstructural, magnetic, electrical and magnetotransport properties. The X-ray diffraction patterns have been analyzed by Rietveld refinement. It revealed that the sample crystallized in a tetragonal structure with the space group I4/mmm and that, as an impurity phase, there were traces of an orthorhombic structure corresponding to a simple perovskite with the space group Pnma. The morphology was examined by using scanning electron microscopy, which revealed that it was porous and granular. The presence and purity of all the constituent elements were confirmed by the Energy Dispersive X-ray spectroscopy investigation. Based on magnetization, the inverse of susceptibility, and hysteresis loop, the magnetic behavior of the compound is discussed in detail. The sample displays a phase transition from ferromagnetic (FM) to paramagnetic (PM) at \({\text{T}}_{\text{C}}\), which was determined to be 290.13 K. Between 305 and 360 K, a Griffith phase (GP) was discovered, indicating the existence ofFM clusters in the paramagnetic domains, and the Griffithtemperature was found to be\(\)339 K. The sample can be thought of as spin-glass-like manganite since a significant divergence wasobserved at low temperatures between the magnetization curves M (T) in the zero-field cooling (ZFC) and field cooling (FC) modes. The spin-glass transition temperature was found to be 261 K. The electrical resistivity under both 0 and 1 T magnetic field exhibits metal-to-insulator transition at \({\text{T}}_{\text{M}\text{I}}\) = 152.98 K. The magnetoresistance was observed to decrease with increasing temperature, peaking at 23% at 11 K under 1 T. Total resistivity in magnetic applied fields of 0T and 1T is composed of residual resistivity, weak localization, and electron-electron combinations below \({\text{T}}_{\text{M}\text{I}}\). Above\({\text{T}}_{\text{M}\text{I}}\) and\({{\theta }}_{\text{D}}/2\) (\({{\theta }}_{\text{D}}\)is Debye temperature), the Mott’s 3D variable range hopping mechanism (3D-VRH) governed the electrical conduction, whereas, the adiabatic small polaron hopping model governed it in the range\({{\theta }}_{\text{D}}/2>\text{T}>300\text{K}\). The density of states, mean hopping energy, and mean hopping distance have all been estimated and thoroughly discussed.