Epitaxial growth and strain-related optical properties of polar magnetic PbVO3 thin films

Tetrahedron-based perovskite PbVO3 (PVO) is an intriguing polar magnetic material because its strong tetragonal distortion allows VO5 square-pyramidal structure rather than VO6 octahedron. Bulk PVO is known to show the unique features of 2-dimensional antiferromagnetic ordering and large pyroelectric polarization. In a single-crystal bulk, the ground state of magnetic ordering of PVO is degenerated by Cand G-type configurations [1] and its transition temperature is reported as TN=47 K [2]. In this study, we fabricated epitaxial PVO thin films on LaAlO3 (LAO) (001) and SrTiO3 (STO) (001) substrates by pulsed laser deposition with off-stoichiometric condition [3]. Structural properties of the epitaxial PVO thin films with respect to mechanical strain induced by lattice mismatch with substrates were investigated by X-ray diffraction, high-resolution transmission electron microscopy, Raman scattering spectroscopy. As a result, abnormal lattice elongation of the PVO thin films along c-axis and consequent octahedral distortion were observed. Our magnetic measurement exhibits a clue for this exotic phase at low temperature, which is a direct evidence for change of the exchange interaction between two adjacent dxy electrons of the V ions. The phenomenon is attributed to the elongation of the c-axis lattice parameter of the PVO thin-films. In addition, the experimental characterizations of linear and nonlinear optical properties for the PVO thin films were performed through spectroscopic ellipsometry and second harmonic generation (SHG), respectively. Symmetry breaking along c-axis in PVO thin films were demonstrated by using SHG signal with nonlinear susceptibility and Fresnel’s formula fitting.