Investigation of chemical pressure effect on magneto-electrical properties in La1.4Ca1.6Mn2O7 manganites

In this study, a detailed study was done about the doped-layered perovskite structure under the influence of chemical pressure as the formation of (La1- yREy)1.4Ca1.6Mn2O7. The effect of chemical pressure was examined by altering the A-site radius, 〈𝑟𝐴 〉 , by doping with the Rare Earths (RE) (Gd, Sm, Nd, Pr) in different proportions (y) and three series of compounds were prepared, with three different 〈𝑟𝐴 〉, 1.3213, 1.3353, 1.3423 Å, by solid-state reaction method. The micro-structural characterization was studied by using X-ray powder diffraction (XRD), Rietveld structural refinements, scanning electron microscopy and X-ray analysis (EDX). The electrical transport properties were determined in the temperature range of 5-300 K under a 0.4 T magnetic field. The metal-insulator (M-I) transition temperature (TM-I) and magnetoresistance (MR) values were determined. The A.C susceptibility measurements were performed to obtain the ferromagnetic (FM)-antiferromagnetic (AFM) phase transition temperature (Tc). All samples were crystallized in the I4/mmm space group in the tetragonal structure and a nonlinear increase in unit cell volume with increasing 〈𝑟𝐴 〉. The particle size distribution is almost homogenous and the EDX spectrum confirmed that all elements present in all samples without any loss of integrated elements. All samples execute the typical M-I and FM-AFM phase transition and with increasing 〈𝑟𝐴 〉, TMI and Tc shift towards higher values. The largest MR (55.09 % at 73K) was observed on the LPCMO material within the group with the smallest 〈𝑟𝐴 〉. The results indicated that the chemical pressure could affect electromagnetic transfer properties by altering the strength of the carrier localization effect. KEYWORDS: Double layered manganites, Chemical Pressure, Electro-magnetic transport, Magnetoresistance