Investigation of hole-doping effect on structural, magnetic properties and magnetoresistance via Gd-site substitution by Pb in the layered manganite La0.1Gd0.2−xPbxCa1.2Sr0.6Mn2O7 (0 ≤ x ≤ 0.2)

In this work, the hole-doping double-layered manganites with formula \({\mathrm{La}}_{1.0}{\mathrm{Gd}}_{(0.2-x)}{\mathrm{Pb}}_{\mathrm{x}}{\mathrm{Ca}}_{1.2}{\mathrm{Sr}}_{0.6}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}\) (x = 0, 0.1, and 0.2) are prepared by the solid-state reaction route and experimentally characterized. The samples' crystallization into a tetragonal structure with an I4/mmm space group was confirmed by Rietveld refinement results of the XRD diffraction patterns using the FullProf software. The results were thoroughly studied after it was discovered that the cell parameters were decreasing. The structure was granular and porous, with grains that resembled spheres, according to micrographs obtained using a scanning electron microscope (SEM). Fourier-transform infrared (FTIR) analysis shows that our samples' characteristic vibrational bands are present. The entire temperature range of 0 to 300 K was used to evaluate electrical resistivity both in the absence and in the presence of an applied magnetic field. The increase in bandwidth, which is determined from the Rietveld refinement results, is found to explain why the \(\rho (T)\) lowers with increasing Pb concentrations for a given temperature. The calculated magnetoresistance (MR%) for sample with x = 0.1 fell to 24.62% at 8 K for x = 0.2 from a maximum value of 30.01% at 5 K under 1 T of applied magnetic field. These values give our samples the opportunity to be good candidates in temperature and magnetic sensors in the cryogenic domains at low magnetic field. Residual resistivity, weak localization, electron–electron, and/or electron–phonon combinations fit the resistivity curves well in the low temperature region. The resistivity curves' fitting revealed that the adiabatic tiny polaron hopping model and Mott’s 3D variable range hopping mechanism (3D-VRH) are both effective at controlling electrical conduction above \({\mathrm{T}}_{\mathrm{MI}}\) and below Debye temperature, respectively. Based on Mott’s 3D-VRH model, the density of states near the Fermi level \((\mathrm{DOS})\), mean hopping distance \({\mathrm{R}}_{\mathrm{h}}\), and mean hopping energy \({\mathrm{E}}_{\mathrm{h}}\) of the charge carriers have been carried out and discussed. On the basis of measurements of magnetization, inverse susceptibility, and loop hysteresis, the samples’ magnetic properties are thoroughly described and discussed. The samples show a magnetic phase change from the ferromagnetic to the paramagnetic phase at Curie temperature \({\mathrm{T}}_{\mathrm{C}}\). Griffith phase temperature was determined to be above \({\mathrm{T}}_{\mathrm{C}}\) based on the inverse of susceptibility’s temperature dependency.