Magnetic criticality and the Griffiths phase modulation through particle size engineering in La_0.7Sr_0.3MnO₃system

This study reports the correlation between structural, magnetic, magnetocaloric, and critical behavior of polycrystalline La_0.7Sr_0.3MnO₃(LSMO) manganites. The samples, with different particle sizes ranging from 17 to 254 nm, were synthesized via a citrate-based sol-gel method accompanied by sintering at different temperatures. X-ray diffraction analysis confirms the phase formation of LSMO, having a rhombohedral structure with thespace group. Magnetization studies reveal a ferromagnetic (FM) to paramagnetic phase transition with Curie temperature () above room temperature (RT). Griffiths phase (GP) is observed in the surroundings of, and is gradually suppressed with enhancing particle size and applied magnetic field. This behavior is attributed to quenched disorder and magnetic phase inhomogeneities. Landau analysis confirms the second-order phase transition for all the LSMO samples. Critical exponent analysis indicates that the mean field model adequately describes the FM regime for samples with particle sizes between 17 to 118 nm, whereas the 3D Heisenberg model provides a better fit for higher particle sizes. The critical behavior aroundand the associated universality class are systematically examined using Arrott plots, Kouvel-Fisher analysis, critical isotherms and magnetic entropy scaling. This investigation suggests that tuning the particle size in the LSMO manganite system enables the identification of a potential magnetic refrigeration material above RT. Moreover, the observed GP in nanocrystalline particles may presumably influence the formation of skyrmion-like magnetic bubbles in the centrosymmetric LSMO manganite system.