J.D. Burton

Suppression of Octahedral Tilts and Associated Changes in Electronic Properties at Epitaxial Oxide Heterostructure Interfaces

Epitaxial oxide interfaces with broken translational symmetry have emerged as a central paradigm behind the novel behaviors of oxide superlattices. Here, we use scanning transmission electron microscopy to demonstrate a direct, quantitative unit-cell-by-unit-cell mapping of lattice parameters and oxygen octahedral rotations across the BiFeO3-La0.7 Sr0.3 MnO3 interface to elucidate how the change of crystal symmetry is accommodated. Combined with low-loss electron energy loss spectroscopy imaging, we demonstrate a mesoscopic antiferrodistortive phase transition near the interface in BiFeO3 and elucidate associated changes in electronic properties in a thin layer directly adjacent to the interface.

Enhanced tunnelling electroresistance effect due to a ferroelectrically induced phase transition at a magnetic complex oxide interface

The range of recently discovered phenomena in complex oxide heterostructures, made possible owing to advances in fabrication techniques, promise new functionalities and device concepts. One issue that has received attention is the bistable electrical modulation of conductivity in ferroelectric tunnel junctions (FTJs) in response to a ferroelectric polarization of the tunnelling barrier, a phenomenon known as the tunnelling electroresistance (TER) effect. Ferroelectric tunnel junctions with ferromagnetic electrodes allow ferroelectric control of the tunnelling spin polarization through the magnetoelectric coupling at the ferromagnet/ferroelectric interface. Here we demonstrate a significant enhancement of TER due to a ferroelectrically induced phase transition at a magnetic complex oxide interface. Ferroelectric tunnel junctions consisting of BaTiO3 tunnelling barriers and La(0.7)Sr(0.3)MnO3 electrodes exhibit a TER enhanced by up to ~10,000% by a nanometre-thick La(0.5)Ca(0.5)MnO3 interlayer inserted at one of the interfaces. The observed phenomenon originates from the metal-to-insulator phase transition in La(0.5)Ca(0.5)MnO3, driven by the modulation of carrier density through ferroelectric polarization switching. Electrical, ferroelectric and magnetoresistive measurements combined with first-principles calculations provide evidence for a magnetoelectric origin of the enhanced TER, and indicate the presence of defect-mediated conduction in the FTJs. The effect is robust and may serve as a viable route for electronic and spintronic applications.

Magnetic Tunnel Junctions with Ferroelectric Barriers: Prediction of Four Resistance States from First Principles

Magnetic tunnel junctions (MTJs), composed of two ferromagnetic electrodes separated by a thin insulating barrier layer, are currently used in spintronic devices, such as magnetic sensors and magnetic random access memories. Recently, driven by demonstrations of ferroelectricity at the nanoscale, thin-film ferroelectric barriers were proposed to extend the functionality of MTJs. Due to the sensitivity of conductance to the magnetization alignment of the electrodes (tunneling magnetoresistance) and the polarization orientation in the ferroelectric barrier (tunneling electroresistance), these multiferroic tunnel junctions (MFTJs) may serve as four-state resistance devices. On the basis of first-principles calculations, we demonstrate four resistance states in SrRuO(3)/BaTiO(3)/SrRuO(3) MFTJs with asymmetric interfaces. We find that the resistance of such a MFTJ is significantly changed when the electric polarization of the barrier is reversed and/or when the magnetizations of the electrodes are switched from parallel to antiparallel. These results reveal the exciting prospects of MFTJs for application as multifunctional spintronic devices.

Prediction of electrically induced magnetic reconstruction at the manganite/ferroelectric interface

The control of magnetization via the application of an electric field, known as magnetoelectric coupling, is among the most fascinating and active research areas today. In addition to fundamental scientific interest, magnetoelectric effects may lead to new device concepts for data storage and processing. There are several known mechanisms for magnetoelectric coupling that include intrinsic effects in single-phase materials, strain-induced coupling in two-phase composites, and electronically driven effects at interfaces. Here we explore a different type of magnetoelectric effect at a ferromagnetic-ferroelectric interface: magnetic reconstruction induced by switching of electric polarization. We demonstrate this effect using first-principles calculations of a

Magnetoelectric effect at the SrRuO3/BaTiO3 (001) interface: An ab initio study

{\text{La}}_{1\ensuremath{-}x}{A}_{x}{\text{MnO}}_{3}/{\text{BaTiO}}_{3}

Enhancement of Ferroelectric Polarization Stability by Interface Engineering

(001) interface, where

Electric modulation of magnetization at the BaTiO3/La0.67Sr0.33MnO3 interfaces

A

Giant tunneling electroresistance effect driven by an electrically controlled spin valve at a complex oxide interface.

is a divalent cation. By choosing the doping level

Atomic and electronic structure of the CoFeB∕MgO interface from first principles

x

Organic Multiferroic Tunnel Junctions with Ferroelectric Poly(vinylidene fluoride) Barriers

to be near a transition between magnetic phases we show that the reversal of the ferroelectric polarization of