Investigation of the impact of A-site cation disorder on the structure, magnetic properties, and magnetic entropy change of trisubstituted divalent ions in La(Ba,Ca,Sr)MnO manganite

This study investigates the effect of A-site disorder, characterized by the average ionic radius (〈 r A 〉) and the cation mismatch ( σ 2 ), on the structural, magnetic, critical behavior, and magnetic entropy changes in La 0.7 (Ba,Ca,Sr) 0.3 MnO 3 manganites with trisubstituted Ba, Ca, and Sr. The sol-gel method was used to prepare polycrystalline samples. All series of compounds crystallize in rhombohedral symmetry with the R 3&cmb.macr; c space group. A linear relationship between lattice parameters, unit cell volume, and 〈 r A 〉 was observed. This reveals an unusual behavior in the correlation between 〈 r A 〉 and σ 2 concerning magnetic properties, which is attributed to the complex simultaneous trisubstitution of divalent ions. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were utilized to validate the chemical composition of compounds. All the samples crystallized in rhombohedral symmetry, and the lattice parameters increased continuously with increasing 〈 r A 〉. A-site disorder causes distortions in the Mn-O bond length and Mn-O-Mn bond angle in the MnO 6 octahedral structure, which influences the double-exchange interaction and electronic bandwidth ( W ). The Curie temperature ( T C ) increases linearly with increasing W . The critical behavior around T C for all the samples was investigated by determining the values of the critical exponents ( β , γ , and δ ) using the modified Arrott plot (MAP) method. The estimated critical exponents show that the unconventional model establishes a short-range ferromagnetic order. The maximum magnetic entropy change (−Δ S M ) was obtained with the lowest 〈 r A 〉 and σ 2 value. The analysis of the critical behavior and universal curve indicates a second-order phase transition (SOPT) nature for all samples. This study investigates the effect of A-site disorder, (ionic radius (〈 r A 〉) and the cation mismatch ( σ 2 )) on the structural, magnetic, critical behavior, and magnetic entropy changes of in La 0.7 (Ba,Ca,Sr) 0.3 MnO 3 manganites.