Epitaxially grown La-modified BiFeO3 magnetoferroelectric thin films

Effects of the La modification on the structure and magnetoferroelectric properties of ${\mathrm{BiFeO}}_3$ (BFO)-based films were examined. On ${\mathrm{SrTiO}}_3$ (001) planes, all the BFO-based films (for $x$ between 0 and 0.15 in ${\mathrm{Bi}}_{1-x}{\mathrm{La}}_x{\mathrm{FeO}}_3$ with the film thickness of 300 nm) were grown epitaxially along [001] direction of tetragonal symmetry. However, the La modification gradually changes the film structure from a monoclinically tilted state to a nontilted tetragonal-like state. Both extended x-ray absorption fine structure and x-ray absorption near edge structure spectra revealed the presence of a strong in-plane compressive stress. Room-temperature magnetization-field curves indicated that the saturation magnetization of these BFO-based epitaxial films increased with the degree of La modification. La-modified BFO film capacitors fabricated on ${\mathrm{SrRuO}}_3$ -buffered ${\mathrm{SrTiO}}_3$ (001) substrates showed fatigue-free ferroelectric switching characteristics up to $4\times {10}^{10}$ read∕write cycles at a frequency of 1 MHz.