Origin of Multiferroism of Ion Doped at Different Sites: Bi₄Ti₃O₁₂ Bulk and Nanoparticles

Abstract

Based on a microscopic model and the Green’s function theory we have investigated the temperature, size, magnetic field and ion doping dependence of the magnetic, electric and dielectric properties in Fe‐and Nd‐doped ferroelectric Bi4Ti3O12‐bulk and nanoparticles. The multiferroisms can be achieved in two ways. At once the magnetism appears by substitution of the nonmagnetic Ti4+ ion with Fe3+, or other transition metal ions in bulk Bi4Ti3O12. Otherwise, the simultaneous existence of Fe3+ and Fe4+ giving rise to a super‐exchangenism responsible for the ferromagnetic interaction. Moreover, multiferoism is possible also in pure Bi4Ti3O12 nanoparticles. Due to surface effects and oxygen vacancies leading to different valence states on the surface of Ti3+ or Ti2+ with spin value S≠0 there appears weak magnetism, which can be improved by Fe ion doping. We demonstrate that doping with rare earth ions, for example Nd3+, at the Bi3+ site is able to improve the ferroelectric, multiferroic and dielectric properties.This article is protected by copyright. All rights reserved.