The structural dependence of magnetization in $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3$ thin films deposited on ${\left(\mathrm{La}\mathrm{Al}{\mathrm{O}}_3\right)}_{0.3}{\left({\mathrm{Sr}}_2\mathrm{Al}\mathrm{Ta}{\mathrm{O}}_6\right)}_{0.7}$ (001) substrate has been investigated in the film thickness $\left(t\right)$ range of $40–500\mathrm{nm}$. High-resolution x-ray-diffraction studies reveal a thickness dependent structural transition from a fully strained tetragonal phase for films with $t⩽75\mathrm{nm}$ to a partially strained and/or relaxed rhombohedral phase in films thicker than $110\mathrm{nm}$, via a coexistence of fully and partially strained phases in the thickness of $75>t>110\mathrm{nm}$. The fully strained phase could also be partially induced in $110\text{−}\mathrm{nm}$ films by increasing the post-deposition ${\mathrm{O}}_2$ annealing pressure. The films $⩾110\mathrm{nm}$ were found to possess a thickness independent bulklike magnetic moment. A weak enhancement in magnetic moment (up to $\sim 0.1{\mu }_{\mathrm{B}}$) is observed in fully strained films $(t⩽75\mathrm{nm})$ and in excessive ${\mathrm{O}}_2$-annealed $110\text{−}\mathrm{nm}$ films having a fraction of strained phase. These results suggest that by a considerably weak magnetic moment in the pseudomorphic strained phase arises from the epitaxial strain induced canted antiferromagnetic structure. This study resolves a much debated issue of strain induced magnetic moment in $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3$ thin films.

• Received 21 September 2006

DOI:https://doi.org/10.1103/PhysRevB.75.060405