Oxygen-vacancy-controlled magnetic properties with magnetic pole inversion in BiFeO₃-based multiferroics

Oxygen vacancies which are generally present in ferrite oxide may significantly affect their magnetic properties. A comprehensive understanding of the relationship between oxygen vacancies and magnetism is of great importance. In this work, we report an oxygen vacancy concentration dependence of magnetism in a single-phase multiferroic BiFeO₃ (BFO)-based system. The BiFeO₃-DyFeO₃ (BDFO) solid solution is synthesized with controlled oxygen vacancies and is characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and AC impedance spectroscopy. The magnetic properties, especially magnetic pole inversion, are found to be highly dependent on oxygen vacancy concentration. The oxygen vacancies generate a Weiss molecular field on the Dy³⁺ ions in the magnetic field range of 570-1000 Oe depending on the oxygen vacancy concentration, and result in a residual net magnetization by breaking the balance between the two nearly antiparallel spin lattices of Fe³⁺ ions. This work demonstrates an effective way to control oxygen vacancies and thereby the magnetic properties and sheds light on the relationship between oxygen vacancies and magnetism in BFO-based multiferroics.