Multiple structural transitions driven by spin-phonon couplings in a perovskite oxide

TL;DR

This study demonstrates that spin-phonon couplings in BiCoO₃ are crucial for understanding its phase diagram and can induce multiple structural transitions, with potential for multifunctional applications through doping.

Contribution

The paper reveals the significant role of spin-phonon interactions in BiCoO₃, showing their impact on phase transitions and proposing ways to harness these effects at ambient conditions.

Findings

Spin-phonon interactions are essential for reproducing BiCoO₃'s phase diagram.

Under compression, these couplings cause a double-reentrant sequence of ferroelectric transitions.

Chemical doping can enable similar effects at ambient conditions.

Abstract

Spin-phonon interactions are central to many interesting phenomena, ranging from superconductivity to magnetoelectric effects. Yet, they are believed to have a negligible influence on the structural behavior of most materials. For example, magnetic perovskite oxides often undergo structural transitions accompanied by magnetic signatures whose minuteness suggests that the underlying spin-phonon couplings are largely irrelevant. Here we present an exception to this rule, showing that novel effects can occur as a consequence. Our first-principles calculations reveal that spin-phonon interactions are essential to reproduce the experimental observations on the phase diagram of magnetoelectric multiferroic BiCoO$_{3}$. Moreover, we predict that, under compression, these couplings lead to an unprecedented temperature-driven double-reentrant sequence of ferroelectric transitions. We propose how to modify BiCoO$_{3}$ via chemical doping to reproduce such striking effects at ambient conditions, thereby yielding useful multifunctionality.