Effect of doping concentration on Gd_1−xAl_xMnO₃ structure and magnetic properties

Gd_1−xAl_xMnO₃ 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 T_irr, then to the superparamagnetic behavior at very low temperatures T_B. While for the sample x = 1 illustrates only two magnetic phases; from the paramagnetic order to the antiferromagnetic phase at T_irr. 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.