Magnetic criticality and the Griffiths phase modulation through particle size engineering in La 0.7 Sr 0.3 MnO ₃ system

This study reports the correlation between structural, magnetic, magnetocaloric, and critical behavior of polycrystalline La 0.7 Sr 0.3 MnO 3 (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 the R-3c space group. Magnetisation studies reveal a ferromagnetic (FM) to paramagnetic (PM) phase transition with Curie temperature ( T C ) above room temperature (RT). Griffiths phase (GP) is observed in the surroundings of T C , and is gradually suppressed with enhancing particle size and applied magnetic field. This behaviour 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 behaviour around T C and 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 room temperature. Moreover, the observed GP in nanocrystalline particles may presumably influence the formation of skyrmion-like magnetic bubbles in the centrosymmetric LSMO manganite system.