Correlated structural, magnetic and colossal magnetoresistance properties of La_1-xSr_xMnO₃: Insights from XPS and ⁵⁵Mn IFNMR

We report the structural, magnetic, and colossal magnetoresistance (CMR) properties of Sr²⁺ − doped lanthanum manganites La_{1- x} Sr _x MnO₃ ( x = 0.3, 0.4, 0.5) (LSMO) synthesized via the gel combustion method. X – ray diffraction (XRD) confirmed the formation of a single – phase rhombohedral perovskite structure (space group R 3̅ c ), with refined lattice parameters showing a systematic decrease in the c -axis and crystallite sizes increasing from 20.85 to 23.02 nm as Sr²⁺ content increased. Fourier-transform infrared (FTIR) spectra exhibited Mn – O bending (∼ 500 cm⁻¹) and stretching (∼ 640 cm⁻¹) modes, with peak shifts and intensity changes confirming lattice strain and successful Sr²⁺ substitution. Raman spectroscopy revealed eight phonon modes (199–727 cm⁻¹), including A_1g and E_g symmetries, indicating local lattice distortions and Jahn – Teller effects due to Sr²⁺ doping. Magnetic properties were studied using vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR). VSM results showed decreasing saturation magnetization ( M _S ) (57.10–34.69 emu/g) and increasing coercivity with Sr²⁺ doping, attributed to reduced double exchange interactions and increased Mn⁴⁺ content. FMR analysis showed enhanced g -factors (>2.00), with low – temperature data (77 K) indicating increased ferromagnetic ordering and static Jahn – Teller distortion. X – ray photoelectron spectroscopy (XPS) and ⁵⁵Mn internal field nuclear magnetic resonance (IFNMR) were employed to analyze oxidation states and local magnetic environments, quantifying Mn³⁺/Mn⁴⁺ ratios and their role in magnetic behavior. CMR properties measured at 77 K revealed significant magnetoresistance, affirming the potential of these materials for applications in magnetic sensing, data storage, and spintronic devices.