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

Abstract

Perovskite oxides ABO3 continue to be a major focus in materials science. Of particular interest is the interplay between A and B 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 (T C) of 10 K. However, the application of external pressure to the EuIIVIIIO2H bulk or compressive strain from the substrate in the thin films induces ICT from the EuIIH layer to the VIIIO2 layer due to the extended empty V d xy orbital. The ICT phenomenon causes the VO2 layer to become conductive, leading to an increase in T C that is dependent on the number of carriers in the d xy 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.

Intersite Charge Transfer through Eu 4f Band Engineering in Eu1–xSrxVO2H Oxyhydride Films

“…(c and d) Schematic illustrations of electronic structures upon ICT. In the previous work, electron doping was controlled by broadening the V 3d xy bandwidth via biaxial strain to EuVO 2 H thin films from the substrate (c), while in this work, it can be controlled by Eu 4f band engineering through Sr substitution (d).…”

“…Notably, the application of pressure (≳16 GPa) to bulk or compressive strain (−0.6%) to thin films imposed by a SrTiO 3 (STO) substrate induces intersite charge transfer (ICT) from Eu II H to V III O 2 layers. The observed ICT is closely associated with the extended empty V 3d xy orbitals (Figure b), leading to electron transfer from the Eu 4f band (Figure c) . Despite unsuccessful attempts to inject carriers through cation substitution, , the electron doping driven by ICT enables the metallization of the Mott insulating VO 2 layers.…”

“…The magnetic properties based on the EuH layer also significantly change as a result of ICT. EuVO 2 H exhibits ferromagnetism associated with Eu 2+ (4f 7 ; J = 7 / 2 ) with a Curie temperature ( T C ) of ∼10 K, surpassing those of other ferromagnetic Eu 2+ -based perovskites. − The introduction of ICT induces a 4-fold increase in T C , accompanied by a pronounced perpendicular magnetic anisotropy (PMA) comparable to that observed in the widely used permanent magnet Nd 2 Fe 14 B . Despite the unclear origin of this phenomenon, PMA in EuVO 2 H is distinct from that of conventional magnetic compounds due to the absence of orbital angular momentum in Eu 2+ ( L = 0).…”

Pure Fluorine Intercalation into Brownmillerite Oxide Thin Films by Using Ionic Liquid Gating

“…For example, the oxyfluoride WO 3– x F x exhibits superconductivity, and MoO 3– x F x has a cathodic property . The anion-ordered oxyhydrides such as SrVO 2 H and EuVO 2 H represent a series of a quasi-two-dimensional Mott insulator, attributed to the lack of π-symmetry in the H 1 s orbital, , while the anion-disordered BaTi­(O,H) 3 has been recognized as an effective catalyst for ammonia synthesis, owing to the reactive nature of its hydride ligands . The smaller electronegativity of nitrogen compared to that of oxygen elevates the conduction band of oxynitrides, endowing them with unique functionalities.…”

Mechanochemical Synthesis of Perovskite Oxyhydrides: Insights from Shear Modulus

“…In particular, perovskite oxyhydrides AB O 3– x H x display distinctive properties resulting from the unique characteristics of the H – ligands . For example, the strong basicity of H – renders BaTiO 3– x H x highly efficient as hydrogenation catalysts, while the high reduction potential (−2.25 V vs SHE) and exceptional polarizability enable outstanding hydride ion conductivity while ensuring stability through an oxide framework. , Moreover, the 1s orbital of H – forms a strong σ-bond with e g orbitals, while it is orthogonal to the t 2g orbitals, making the anion-ordered A VO 2 H ( A = Sr, Eu) (Figure S2a) a two-dimensional Mott insulator. , …”