BiFeO3/La0.7Sr0.3MnO3 heterostructures deposited on Spark Plasma Sintered LaAlO3 Substrates

Multiferroic BiFeO3 (BFO) / La0.7Sr0.3MnO3 heterostructured thin films were grown by pulsed laser deposition on polished spark plasma sintered LaAlO3 (LAO) polycrystalline substrates. Both polycrystalline LAO substrates and BFO films were locally characterized using electron backscattering diffraction (EBSD), which confirmed the high-quality local epitaxial growth on each substrate grain. Piezoforce microscopy was used to image and switch the piezo-domains, and the results are consistent with the relative orientation of the ferroelectric variants with the surface normal. This high-throughput synthesis process opens the routes towards wide survey of electronic properties as a function of crystalline orientation in complex oxide thin film synthesis.Comment: 10 pages, 4 figures, Submitted to Applied Physics Letter

Ferroelectric polarization switching with a remarkably high activation energy in orthorhombic GaFeO3 thin films

This work was supported by the National Research Foundation (NRF) Grants funded by the Korea Government (MSIP) (Grant No. 2012R 1A1A2041628 and 2013R 1A2A2A01068274). The work at Cambridge was supported by the Engineering and Physical Sciences Research Council (EPSRC). AG and RG thank the Department of Science and Technology for the financial support (Grant No. SB/S3/ME/29/2013).Orthorhombic GaFeO3 (o-GFO) with the polar Pna21 space group is a prominent ferrite owing to its piezoelectricity and ferrimagnetism, coupled with magnetoelectric effects. Herein, we demonstrate large ferroelectric remanent polarization in undoped o-GFO thin films by adopting either a hexagonal strontium titanate (STO) or a cubic yttrium-stabilized zirconia (YSZ) substrate. The polarization-electric-field hysteresis curves of the polar c-axis-grown o-GFO film on a SrRuO3/STO substrate show the net switching polarization of ~35 μC cm−2 with an unusually high coercive field (Ec) of ±1400 kV cm−1 at room temperature. The positive-up and negative-down measurement also demonstrates the switching polarization of ~26 μC cm−2. The activation energy for the polarization switching, as obtained by density-functional theory calculations, is remarkably high, 1.05 eV per formula unit. We have theoretically shown that this high value accounts for the extraordinary high Ec and the stability of the polar Pna21 phase over a wide range of temperatures up to 1368 K.Publisher PDFPeer reviewe

Kinetics of ferroelectric switching in poled barium titanate ceramics: Effects of electrical cycling rate

Our understanding of the rate-dependent electro-mechanical response of ferroelectric ceramics is incomplete primarily due to limited experimental data characterizing the material behavior at high rates (or short time scales). Therefore, we experimentally study the effect of cycling rate on polarization switching in poled barium titanate (BaTiO3) ceramics across five orders of magnitude in cycling rate. Mechanical strain data as a function of the applied electric field were collected across three orders of magnitude. We quantify the rate-dependent coercive field, remanent and peak polarization, apparent permittivity and apparent piezoelectric coefficient, and actuation strain. Results reveal a reduction in polarizability of the material with increasing rate and a strong asymmetry in the electromechanical hystereses, which comes with differences in the rate dependence when loading parallel vs. anti-parallel to the direction of poling. Supported by a simple model and ex-situ piezoresponse force microscopy, we conclude that rate effects arise from the mobility of 90 domain walls and the competition between nucleation and growth of domains. The asymmetric hysteresis highlights the importance of point charge and dipole defects, which affect the domain wall kinetics and hence the rate effects of polarization switching through the competing time scales of space charge migration, dipole reorientation, and domain wall activity.ISSN:2589-152

Magnetoelectric force microscopy on antiferromagnetic 180 degree domains in Cr2O3

Magnetoelectric force microscopy (MeFM) is characterized as methodical tool for the investigation of antiferromagnetic domain states, in particular of the 180 ∘ variety. As reference compound for this investigation we use Cr 2 O 3 . Access to the antiferromagnetic order is provided by the linear magnetoelectric effect. We resolve the opposite antiferromagnetic 180 ∘ domain states of Cr 2 O 3 and estimate the sensitivity of the MeFM approach, its inherent advantages in comparison to alternative techniques and its general feasibility for probing antiferromagnetic order

The ultrathin limit of improper ferroelectricity

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