Size effects in multiferroic BiFeO3 nanodots: A first-principles-based study

TL;DR

This study uses a first-principles-based effective Hamiltonian to explore how the size of BiFeO3 nanodots influences their structural and magnetic properties, revealing size-dependent phase transitions and critical thickness effects.

Contribution

It introduces a novel effective Hamiltonian approach to analyze size effects in BiFeO3 nanodots, uncovering scaling laws and critical size thresholds for their properties.

Findings

Magnetic and electric transition temperatures scale inversely with nanodot size.

Structural phases in bulk are suppressed at nanoscale due to size effects.

A critical thickness of about 1.6 nm exists below which long-range order vanishes.

Abstract

An effective Hamiltonian scheme is developed to investigate structural and magnetic properties of BiFeO3 nanodots under short-circuit-like electrical boundary conditions. Various striking effects are discovered. Examples include (a) scaling laws involving the inverse of the dots' size for the magnetic and electric transition temperatures; (b) the washing out of some structural phases present in the bulk via size effects; (c) the possibility of tailoring the difference between the Neel and Curie temperatures, by playing with the size and electrical boundary conditions; and (d) an universal critical thickness of the order of 1.6 nm below which the dots do not possess any long-range ordering for the electrical and magnetic dipoles, as well as, for the oxygen octahedral tiltings.