High symmetric SrRuO3 (001) thin films: Perfectly lattice-matched electrodes for multiferroic BiFeO3

Abstract

High symmetric tetragonal (c/a < 1 and c/a > 1) and cubic (c/a = 1) SrRuO3 thin films were developed on SrTiO3 substrate by controlling RF-power and substrate temperature. These SrRuO3 symmetries exhibit larger in-plane lattice parameters (3.936–3.98 Å) compared to bulk orthorhombic SrRuO3 (3.93 Å), and are coincidentally similar to the predicted high temperature tetragonal (>820 K) and cubic (>950 K) SrRuO3 phases. Importantly, the lattice parameters of cubic (c/a = 1) SrRuO3 (3.968 Å) films match very well to the pseudocubic BiFeO3 (3.966 Å), opening new perspectives for BiFeO3/SrRuO3/SrTiO3 heterostructures for spintronics. Due to high crystal symmetry and large unit cell expansion (∇V/V = ∼1.1%-4.2%), a non-Fermi-liquid (R ∝ T3/2) and weak anisotropic magnetic behaviors, and reduced TC's are commonly observed which are different from the orthorhombic SrRuO3.