Large Perpendicular Magnetic Anisotropy Induced by an Intersite Charge Transfer in Strained EuVO₂H Films

Abstract

Perovskite oxides <i>AB</i>O₃ continue to be a major focus in materials science. Of particular interest is the interplay between <i>A</i> and <i>B</i> cations as exemplified by intersite charge transfer (ICT), which causes novel phenomena including negative thermal expansion and metal-insulator transition. However, the ICT properties were achieved and optimized by cationic substitution or ordering. Here we demonstrate an anionic approach to induce ICT using an oxyhydride perovskite, EuVO₂H, which has alternating layers of EuH and VO₂. A bulk EuVO₂H behaves as a ferromagnetic insulator with a relatively high transition temperature (<i>T</i>_C) of 10 K. However, the application of external pressure to the Eu^IIV^IIIO₂H bulk or compressive strain from the substrate in the thin films induces ICT from the Eu^IIH layer to the V^IIIO₂ layer due to the extended empty V d_<i>xy</i> orbital. The ICT phenomenon causes the VO₂ layer to become conductive, leading to an increase in <i>T</i>_C that is dependent on the number of carriers in the d_<i>xy</i> orbitals (up to a factor of 4 for 10 nm thin films). In addition, a large perpendicular magnetic anisotropy appears with the ICT for the films of <100 nm, which is unprecedented in materials with orbital-free Eu²⁺, opening new perspectives for applications. The present results provide opportunities for the acquisition of novel functions by alternating transition metal/rare earth layers with heteroanions.