Magnetic properties of Bi0.5Sr0.5FexMn1−xO3 (⩽x⩽0.7)

Fe-substituted manganites Bi0.5Sr0.5FexMn1−xO3 (0⩽x⩽1.0) were synthesized by a solid-state reaction. X-ray powder diffraction and neutron diffraction investigations performed at room temperature show that the crystal structure is orthorhombic for x⩽ 0.3 and cubic for x>0.4. The unit cell volume increases with x. Magnetic properties were studied between 5 and 1000K in a magnetic field up to 16kOe for the compounds with x⩽0.7. A charge/orbital ordering feature was only observed in magnetization curves for the compound with no Fe. The magnetic state of the compounds with different Fe contents changes from paramagnetic to weak antiferromagnetic below the temperature TN varying in the range of 115–155K. Unusual thermomagnetic behavior in the paramagnetic region was observed, which could be related to a coexistence of antiferromagnetic and ferromagnetic fluctuations far above TN. The typical thermomagnetic zero field cooled/field cooled hysteresis below about 40K can be related to the formation of small ferromagnetic clusters below that temperature. The conductivity of the compounds, measured between 90 and 600K, is of the semiconducting type, and no magnetoresistant effect was observed for any of them in a field of 7kOe.