Effect of doping concentration on Gd1−xAlxMnO3 structure and magnetic properties

Abstract

Gd1−xAlxMnO3 material was successfully synthesized using the Pechini-modified-sol–gel method at different Al doping concentrations (x = 0, 0.25, 0.75, and 1). The samples were structurally characterized using XRD patterns and SEM/EDS analysis. The sample x = 0 displayed a single-phase, while the other systems displayed a multi-phase structure. Particle size calculated using the SEM images confirmed a successful synthesis of nanomaterials in the range of 97 and 123 nm. FC and ZFC magnetization modes were conducted for the samples, and we noticed a gradual decrease in the magnetization values as the doping increases. However, the doping also resulted in shifting the bifurcation temperature to elevated ones. The compound with x = 1 showed a good increase in magnetization up to around 8 emu/g with a bifurcation temperature of 68 K opening the door for different sets of applications at higher temperatures. The three samples (x = 0, 0.25, and 0.75) present different magnetic phases while decreasing the temperature starting from the paramagnetic phase at room temperature to the antiferromagnetic phase at the bifurcation temperature Tirr, then to the superparamagnetic behavior at very low temperatures TB. While for the sample x = 1 illustrates only two magnetic phases; from the paramagnetic order to the antiferromagnetic phase at Tirr. Griffiths phase was also inspected for different doping concentrations, and a proportional relation was drawn between the Griffiths regime and the aluminum percentage. The isothermal entropy measurements were conducted in a magnetic field between 1 and 7 T. The concentration of aluminum in the samples reduces the produced entropy change but widens the temperature difference. The x = 0 sample shows the highest isothermal entropy change and RCP of 50 J.Kg−1.K−1 and 552 J/kg, respectively, at 7 T. Also, the sample with x = 1 showed a maximum entropy change at 50 K due to the formation of an incommensurate antiferromagnetic phase.