Strain-tuned enhancement of ferromagnetic T(C) to 176 K in Sm-doped BiMnO(3) thin films and determination of magnetic phase diagram

BiMnO(3) is a promising multiferroic material but it’s ferromagnetic T(C) is well below room temperature and the magnetic phase diagram is unknown. In this work, the relationship between magnetic transition temperature (T(C)) and the substrate induced (pseudo-) tetragonal distortion (ratio of out-of-plane to in-plane lattice parameters, c/a) in BiMnO(3) thin films, lightly doped to optimize lattice dimensions, was determined. For c/a > 0.99, hidden antiferromagnetism was revealed and the magnetisation versus temperature curves showed a tail behaviour, whereas for c/a < 0.99 clear ferromagnetism was observed. A peak T(C) of up to 176 K, more than 70 K higher than for bulk BiMnO(3), was achieved through precise strain tuning. The T(C) was maximised for strong tensile in-plane strain which produced weak octahedral rotations in the out-of-plane direction, an orthorhombic-like structure, and strong ferromagnetic coupling.