Magnetic Properties and Mossbauer Investigations of La0.67Sr0.33FexMn1-xO3 (x=0 and 0.5) Perovskites

We report magnetic phase separation in pure La0.67Sr0.33FexMn1-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 Fe-57 Mossbauer spectroscopy measurements show the presence of Fe in two different environments that have an AFM Fe3+-O-Mn4+ and Fe3+/2+-O-Fe3+/2+ coordination. The unequal fraction population of Fe ions at both AFM environments seems to increase the exchange bias effect.