Effect of sintering temperature on structural, microstructural and magnetic properties of La 0.8 Sr 0.2 MnO ₃ : Evolution of faceting and terrace like morphology

Perovskite manganites have attracted considerable attention due to their strongly correlated structural, electronic, and magnetic properties arising from the interplay among 'charge', 'spin', and 'orbital' degrees of freedom of Mn '3d' electrons. In this work, La 0.8 Sr 0.2 MnO 3 (LSMO) manganites with systematically varied particle sizes were prepared via a sol-gel technique to investigate the influence of particle size on structural evolution and magnetic behavior. Xray diffraction data after Rietveld analysis substantiates the formation of a monophasic rhombohedral R-3c structure for samples sintered up to 1200 °C, whereas higher sintering temperatures (1350 °C and 1500 °C) lead to the emergence of a minor monoclinic P21 /c secondary phase (∼4-6%) coexisting with the dominant phase. Field emission scanning electron microscopy reveals a significant increase in grain size from ∼97 nm to ∼4.2 µm with enhanced sintering, accompanied by the development of terrace-like surface morphologies indicative of step-flow growth and enhanced crystallinity. These features are attributed to variations in surface chemical potential and critical nucleation processes. Magnetic measurements demonstrate the presence of a Griffiths phase (GP), whose strength progressively diminishes with increasing particle size and applied magnetic field, reflecting reduced magnetic inhomogeneity. The GP behavior is ascribed to quenched disorder and short-range ferromagnetic clustering within a paramagnetic matrix. Temperature-dependent magnetization measurements reveal a ferromagnetic-paramagnetic transition above room temperature. Additionally, the particle size dependence of spin-wave excitations and the 'spin-wave' stiffness constant highlights the role of exchange interactions in governing magnetic dynamics. Overall, the results establish a clear correlation between sintering-temperature-driven structural modifications and magnetic properties, underscoring the potential of LSMO manganites for room-temperature spintronic and magnonic applications.