title: Interplay between size, composition, and phase transition of nanocrystalline Cr(3+)-doped BaTiO3 as a path to multiferroism in perovskite-type oxides.
abstract: Multiferroics, materials that exhibit coupling between spontaneous magnetic and electric dipole ordering, have significant potential for high-density memory storage and the design of complex multistate memory elements. In this work, we have demonstrated the solvent-controlled synthesis of Cr(3+)-doped BaTiO(3) nanocrystals and investigated the effects of size and doping concentration on their structure and phase transformation using X-ray diffraction and Raman spectroscopy. The magnetic properties of these nanocrystals were studied by magnetic susceptibility, magnetic circular dichroism (MCD), and X-ray magnetic circular dichroism (XMCD) measurements. We observed that a decrease in nanocrystal size and an increase in doping concentration favor the stabilization of the paraelectric cubic phase, although the ferroelectric tetragonal phase is partly retained even in ca. 7 nm nanocrystals having the doping concentration of ca. 5%. The chromium(III) doping was determined to be a dominant factor for destabilization of the tetragonal phase. A combination of magnetic and magneto-optical measurements revealed that nanocrystalline films prepared from as-synthesized paramagnetic Cr(3+)-doped BaTiO(3) nanocrystals exhibit robust ferromagnetic ordering (up to ca. 2 μ(B)/Cr(3+)), similarly to magnetically doped transparent conducting oxides. The observed ferromagnetism increases with decreasing constituent nanocrystal size because of an enhancement in the interfacial defect concentration with increasing surface-to-volume ratio. Element-specific XMCD spectra measured by scanning transmission X-ray microscopy (STXM) confirmed with high spatial resolution that magnetic ordering arises from Cr(3+) dopant exchange interactions. The results of this work suggest an approach to the design and preparation of multiferroic perovskite materials that retain the ferroelectric phase and exhibit long-range magnetic ordering by using doped colloidal nanocrystals with optimized composition and size as functional building blocks.
authors.affiliation: Department of Chemistry, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1.
authors.forename: Ling
authors.initials: L
authors.lastname: Ju
authors.forename: Tahereh
authors.initials: T
authors.lastname: Sabergharesou
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Stamplecoskie
authors.forename: Manu
authors.initials: M
authors.lastname: Hegde
authors.forename: Ting
authors.initials: T
authors.lastname: Wang
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Combe
authors.forename: Hongyu
authors.initials: H
authors.lastname: Wu
authors.forename: Pavle V
authors.initials: PV
authors.lastname: Radovanovic