Strain-induced increase of dielectric constant in EuO thin film

Recently, lattice dynamics of the highly strained europium monoxide, as a promising candidate for strong ferroelectric-ferromagnet material, applied in the next-generation storage devices, attracted huge attention in the solid-state electronics. Here, the authors investigate the effect of tensile strain on dielectric properties of pulsed laser deposited EuO thin films from 10 to 200 K. A nearly 3% out-of-plane lattice compression is observed as the film thickness was reduced to 8 nm, which could originate from the lattice mismatch between film and a LaAlO3 substrate. The temperature and frequency dependence of capacitance and loss factor of the films reveals the dominant role of electronic and ionic polarization below 100 K. The interdigitated capacitor fabricated on strained film shows almost 50% increase of capacitance compared to the relaxed one, which corresponds to a considerable increase of dielectric constant induced by in-plane tensile strain. Softening of the in-plane polarized transverse phonon modes of EuO lattice due to tensile strain might have the major contribution to this behaviour according to the Lyddane-Sachs-Teller relation.