Magnetic Properties and Mössbauer Investigations of La_0.67Sr_0.33Fe_xMn_1−xO₃ (x = 0 and 0.5) Perovskites

We report magnetic phase separation in pure La_0.67Sr_0.33Fe_xMn_1−xO₃ (x = 0 and 0.5) ceramic samples. Rhombohedral crystal structures obtained with R3C space group show no significant changes in the lattice structures due to the close values of ionic radii of Fe³⁺ and Mn³⁺ ions. However, significant changes occur in the magnetic properties due to competing ferromagnetic (FM) and antiferromagnetic (AFM) interactions because of the presence of Fe³⁺ substitution. The FM double exchange interactions (DE) (Mn³⁺–O–Mn⁴⁺) appears suppressed by AFM superexchange interactions (Fe³⁺–O–Mn⁴⁺, Fe³⁺–O–Fe³⁺, Mn⁴⁺–O–Mn⁴⁺). The saturation magnetization for x = 0 has the highest value of approximately 80 emu/g at 2 K, which dropped significantly to approximately 5 emu/g at 2 K for the x = 0.5 sample. The coercivity (H_c) for x = 0.5 increased from 161 Oe at 300 K to 786 Oe at 2 K compared with that of x = 0 which varied from 110 to 150 Oe. A value of H_c(0) = 1.5 ± 0.04 kOe was extrapolated from the model fit to the temperature dependence of H_c. The temperature-dependent ⁵⁷Fe Mössbauer spectroscopy measurements show the presence of Fe in two different environments that have an AFM Fe³⁺–O–Mn⁴⁺ and Fe^3+/2+–O–Fe^3+/2+ coordination. The unequal fraction population of Fe ions at both AFM environments seems to increase the exchange bias effect.