Temperature-Driven Transformation of the Crystal and Magnetic Structures of BiFe0.7Mn0.3O3 Ceramics

The compound BiFe0.7Mn0.3O3 consisting at room temperature of coexistent anti-polar orthorhombic and polar rhombohedral phases has a metastable structural state, which has been studied by laboratory X-ray, synchrotron and neutron diffraction, magnetometry, differential thermal analysis, and differential scanning calorimetry. Thermal annealing of the sample at temperatures above the temperature-driven phase transition into the single phase rhombohedral structure (similar to 700 K) causes an increase of the volume fraction of the rhombohedral phase at room temperature from similar to 10% up to similar to 30%, which is accompanied by the modification of the magnetic state, leading to strengthening of a ferromagnetic component. A strong external magnetic field (similar to 5 T) applied to the sample notably changes its magnetic properties, as well as provides a reinforcement of the ferromagnetic component, thus leading to an interaction between two magnetic subsystems formed by the antiferromagnetic matrix with non-collinear alignment of magnetic moments and the nanoscale ferromagnetic clusters coexisting within it. The modification of the structural state and magnetic properties of the compounds and a correlation between different structural and magnetic phases are discussed focusing on the effect of thermal annealing and the impact of an external magnetic field.