Multiferroic Properties of Nanocrystalline BaTiO3

TL;DR

This study demonstrates that nanocrystalline BaTiO3 exhibits multiferroic properties, with ferromagnetism from surface oxygen vacancies and ferroelectricity from the core, enabling room-temperature magnetocapacitance effects.

Contribution

It reveals the emergence of multiferroicity in intermediate-sized nanocrystalline BaTiO3 through combined experiments and simulations, highlighting surface-induced ferromagnetism and core ferroelectricity.

Findings

Multiferroic behavior appears in nanocrystalline BaTiO3.

Surface oxygen vacancies induce ferromagnetism.

Strong coupling leads to room-temperature magnetocapacitance.

Abstract

Some of the Multiferroics [1] form a rare class of materials that exhibit magnetoelectric coupling arising from the coexistence of ferromagnetism and ferroelectricity, with potential for many technological applications.[2,3] Over the last decade, an active research on multiferroics has resulted in the identification of a few routes that lead to multiferroicity in bulk materials.[4-6] While ferroelectricity in a classic ferroelectric such as BaTiO3 is expected to diminish with the reducing particle size,[7,8] ferromagnetism cannot occur in its bulk form.[9] Here, we use a combination of experiment and first-principles simulations to demonstrate that multiferroic nature emerges in intermediate size nanocrystalline BaTiO3, ferromagnetism arising from the oxygen vacancies at the surface and ferroelectricity from the core. A strong coupling between a surface polar phonon and spin is shown to result in a magnetocapacitance effect observed at room temperature, which can open up possibilities of new electro-magneto-mechanical devices at the nano-scale.