Vanadium-doped HfO$_2$, multiferroic uncompromised

TL;DR

This study uses ab initio calculations to demonstrate that low-concentration vanadium doping in orthorhombic hafnia induces multiferroic properties, maintaining ferroelectricity and ferromagnetism with enhanced magnetization.

Contribution

It reveals that vanadium doping in hafnia creates a stable multiferroic phase with preserved polarization and increased ferromagnetic magnetization, a novel combination for this material.

Findings

Vanadium doping induces ferroelectric and ferromagnetic properties.

Magnetization increases linearly with V concentration.

A stable 1 eV gap and significant polarization are maintained.

Abstract

Ab initio density-functional calculations show that orthorhombic Pca21 hafnia HfO2 mixed with vanadium at low concentration is a ferroelectric and ferromagnetic insulator. The multiorbital degeneracy of singly-occupied V states in the nominally 4+ ionic state is broken by magnetism, reduced symmetry, and local distortion, causing a single one-electron majority state per V atom to be occupied. A gap of order 1 eV thus survives at all V concentrations, and intrinsic polarization is preserved, at the level of two-thirds the hafnia value. Ferromagnetic magnetization is found to increase linearly with V content, with values of 30-40 emu/cm3 at concentrations near the end of the stability range.