Variation of local magnetism in a perovskite manganite La 0.7 Ca 0.3 MnO 3 by Fe doping

Fe doping effect on the local magnetic property of La 0.7 Ca 0.3 Mn 1− x Fe x O 3 (0.4 ≤ x ≤ 0.55) was investigated by means of 57 Fe Mössbauer spectroscopy. The X-ray diffraction patterns and the isomer shifts of the 57 Fe Mössbauer spectra demonstrate that all the Fe ions are high-spin trivalent and share the B site lattice positions with Mn ions. The sample of La 0.7 Ca 0.3 Mn 0.6 Fe 0.4 O 3 ( x = 0.4) was found to be in the paramagnetic state even at 8 K. For the samples with high Fe contents, however, magnetic sextet(s) arising from local magnetic ordering were observed in the low-temperature spectrum of La 0.7 Ca 0.3 Mn 0.5 Fe 0.5 O 3 ( x = 0.5), and also in all the spectra of La 0.7 Ca 0.3 Mn 0.45 Fe 0.55 O 3 ( x = 0.55) measured in the range of 8 K—room temperature. These observations suggest that randomly distributed Fe 3+ ions interfere with the double exchange interaction in Mn 3+ –O–Mn 4+ , and antiferromagnetic ordering arises from superexchange interaction in Fe 3+ –O–Fe 3+ at high Fe content.