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18 Aug 2008

Volume 93, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 93, 073101 (2008); http://dx.doi.org/10.1063/1.2970055 (3 pages)

A. J. Du, Y. Chen, G. Q. Lu, and Sean C. Smith
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Crystallographic, magnetic, and ferroelectric structures of bulklike BiFeO3 thin films

H. Béa, M. Bibes, X.-H. Zhu, S. Fusil, K. Bouzehouane, S. Petit, J. Kreisel, and A. Barthélémy

Appl. Phys. Lett. 93, 072901 (2008); http://dx.doi.org/10.1063/1.2940327 (3 pages) | Cited 11 times

Online Publication Date: 18 August 2008

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BiFeO3 thin films deposited on (111)-SrTiO3 substrates present both structural (rhombohedral) and multiferroic properties similar to bulk. The structural relaxation occurring when thickness increases and the low critical thickness possibly indicate different defect types and distribution as compared to (001)-BiFeO3, which may influence multiferroic domain dynamics. The same G-type antiferromagnetic order as in bulk is observed by neutron diffraction, with a superimposed weak ferromagnetic moment (10 emu/cm3) showing a planar anisotropy of 5 kJ/m3. When doped with 5% Mn these films also exhibit a polarization of 95 μC/cm2 along the [111] direction at room temperature, similar to high-quality BiFeO3 single crystals.
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77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
61.66.Fn Inorganic compounds
77.22.Ej Polarization and depolarization

Wedgelike ultrathin epitaxial BaTiO3 films for studies of scaling effects in ferroelectrics

A. Petraru, H. Kohlstedt, U. Poppe, R. Waser, A. Solbach, U. Klemradt, J. Schubert, W. Zander, and N. A. Pertsev

Appl. Phys. Lett. 93, 072902 (2008); http://dx.doi.org/10.1063/1.2972135 (3 pages) | Cited 13 times

Online Publication Date: 18 August 2008

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To study ferroelectric size effects in heteroepitaxial SrRuO3/BaTiO3/SrRuO3 capacitors, ultrathin BaTiO3 layers were deposited in wedge form across SrTiO3 substrates. The wedgelike films were fabricated by using either an off-center substrate-target geometry or via a moveable shutter during high-pressure sputter deposition. The crystallinity, composition, and surface roughness along wedgelike BaTiO3 films were verified by x-ray diffraction, Rutherford backscattering spectrometry, and atomic force microscopy, respectively. The electrical measurements performed at 77 K showed that, despite progressive reduction in remanent polarization as the film thickness decreases even the 3.5-nm-thick BaTiO3 film retains a large remanent polarization of 28 μC/cm2.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
68.35.bt Other materials

The nature of dielectric breakdown

X. Li, C. H. Tung, and K. L. Pey

Appl. Phys. Lett. 93, 072903 (2008); http://dx.doi.org/10.1063/1.2974792 (3 pages) | Cited 25 times

Online Publication Date: 20 August 2008

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Dielectric breakdown is the process of local materials transiting from insulating to conductive when the dielectric is submerged in a high external electric field environment. We show that the atomistic changes of the chemical bonding in a nanoscale breakdown path are extensive and irreversible. Oxygen atoms in dielectric SiO2 are washed out with substoichiometric silicon oxide (SiOx with x<2) formation, and local energy gap lowering with intermediate bonding state of silicon atoms (Si1+, Si2+, and Si3+) in the percolation leakage path. Oxygen deficiency within the breakdown path is estimated to be as high as 50%–60%.
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77.22.Jp Dielectric breakdown and space-charge effects
71.20.Ps Other inorganic compounds

Ferromagnetism and ferroelectricity in highly resistive Pb0.7Sr0.3(Fe0.012Ti0.988)O3 nanoparticles and its conduction by variable-range-hopping mechanism

Kuldeep Chand Verma, M. Singh, R. K. Kotnala, and N. S. Negi

Appl. Phys. Lett. 93, 072904 (2008); http://dx.doi.org/10.1063/1.2973400 (3 pages) | Cited 8 times

Online Publication Date: 20 August 2008

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The enhancement in ferromagnetism and ferroelectricity at room temperature for Pb0.7Sr0.3(Fe0.012Ti0.988)O3 (PSFT) nanoparticles is proved by magnetization and polarization hysteresis loop. The x-ray diffraction and micrograph show that the PSFT nanoparticles have distorted tetragonal single phase, and their average particle’s size is 8 nm. The effect of Sr content reduces the particle size, and hence the multiferroic system becomes more resistive, which dominates the superparamagnetic/paraelectric relaxation. The variable-range-hopping conduction mechanism explained the high resistivity of PSFT nanoparticles, which suggests that the room temperature movement of electrons involves short-range order through defect states.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
75.80.+q Magnetomechanical effects, magnetostriction
72.20.Ee Mobility edges; hopping transport

High speed piezoresponse force microscopy: <1 frame per second nanoscale imaging

Ramesh Nath, Ying-Hao Chu, Nicholas A. Polomoff, Ramamoorthy Ramesh, and Bryan D. Huey

Appl. Phys. Lett. 93, 072905 (2008); http://dx.doi.org/10.1063/1.2969045 (3 pages) | Cited 30 times

Online Publication Date: 22 August 2008

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An atomic force microscopy (AFM) based technique is described for mapping piezoactuation with nanoscale resolution in less than a second per complete image frame. “High speed piezo force microscopy” (HSPFM) achieves this >100× increase in acquisition rates by coupling a commercial AFM with concepts of acoustics. This allows previously inaccessible dynamic studies, including measuring ferroelectric domain nucleation and growth during in situ poling. Hundreds of consecutive images are analyzed with 49 μs temporal resolution per pixel per frame, revealing 32 nucleation sites/μm2 with 36 μm/s average domain velocities. HSPFM images acquired in as fast as 1/10th s are also presented.
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07.79.Lh Atomic force microscopes
77.80.Dj Domain structure; hysteresis

Thermal noise cancellation in symmetric magnetoelectric bimorph laminates

Junyi Zhai, Zengping Xing, Shuxiang Dong, Jiefang Li, and D. Viehland

Appl. Phys. Lett. 93, 072906 (2008); http://dx.doi.org/10.1063/1.2969794 (3 pages) | Cited 10 times

Online Publication Date: 22 August 2008

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We have found a symmetric Terfenol-D/Pb(Zr,Ti)03 (PZT) bimorph magnetoelectric (ME) laminate, which operates in a bending mode under an unsymmetrical (U-shaped) magnetic bias. It has a giant ME voltage coefficient of about 70 V/cm Oe at resonance. Unlike other symmetric ME laminate structures, the symmetric bimorph structure has the capability to reject thermal noise from a magnetic signal, due to its back-to-back structure. The mechanism for the thermal noise cancellation capability is that the laminate operates in a bending mode (out charges of reverse sign), whereas the thermal noise is contained in a longitudinal mode (out charges have the same sign, allowing cancellation by differential detection).
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72.70.+m Noise processes and phenomena
75.80.+q Magnetomechanical effects, magnetostriction
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