Ferroelectric Polarization Induced Selective Growth of BiFeO3 Nanocrystals with a Remarkable Ferromagnetism

Abstract

Bringing BiFeO3 (BFO) into a size below 62 nm is a promising approach to improve its ferromagnetism by breaking a period of the superimposed cycloidal spin structure. It has been well investigated that a low nucleation rate and a high growth rate in solution usually leads to a large crystal size of BFO ranging from several hundred nanometers to micrometers. In this work, we propose that a polar surface can be employed to induce a selective growth of BFO nanocrystals via a hydrothermal method. BFO nanocrystals with a uniform size of 30–50 nm have been found to selectively and epitaxially grow on the negative polar surface of single‐crystal and single‐domain ferroelectric PbTiO3 (PTO) nanoplates. It was revealed that the positively charged Bi25FeO40 precursors adsorbed on the negative polar surface to screen the polarization, and subsequent BFO nanocrystals nucleated in a large scale via Bi25FeO40 dissolution confined with the surface of the nanoplates, giving rise to a small and uniform size. Importantly, an obvious ferromagnetism has been observed in BFO/PTO nanocomposites with a saturation magnetization of 0.13 emu/g (normalized to the mass fraction of BFO of ca. 20.5wt.‐%) and a coercive field of 662 Oe. The findings suggest that a polar surface could be highly effective to tailor the crystal growth and properties of other oxide materials.