The Effects of Multiphase Formation on Strain Relaxation and Magnetization in Multiferroic BiFeO₃ Thin Films

Abstract

Abstract Multiferroic epitaxial Bi‐Fe‐O thin films of different thicknesses (15–500 nm) were grown on SrTiO 3 (001) substrates by pulsed laser deposition under various oxygen partial pressures to investigate the microstructural evolution in the Bi‐Fe‐O system and its effect on misfit strain relaxation and on the magnetic properties of the films. Films grown at low oxygen partial pressure show the canted antiferromagnetic phase α‐Fe 2 O 3 embedded in a matrix of BiFeO 3 . The ferromagnetic phase, γ‐Fe 2 O 3 is found to precipitate inside the α‐Fe 2 O 3 grains. The formation of these phases changes the magnetic properties of the films and the misfit strain relaxation mechanism. The multiphase films exhibit both highly strained and fully relaxed BiFeO 3 regions in the same film. The magnetization in the multiphase Bi‐Fe‐O films is controlled by the presence of the γ‐Fe 2 O 3 phase rather than heteroepitaxial strain as it is the case in pure single phase BiFeO 3 . Also, our results show that this unique accommodation of misfit strain by the formation of α‐Fe 2 O 3 gives rise to significant enhancement of the piezo electric properties of BiFeO 3.