Strain-tuned enhancement of ferromagnetic T$_{C}$ to 176 K in Sm-doped BiMnO$_{3}$ thin films and determination of magnetic phase diagram

Abstract

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.