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10 Aug 2009

Volume 95, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 062501 (2009); http://dx.doi.org/10.1063/1.3200226 (3 pages)

O. Vávra, W. Pfaff, and Ch. Strunk
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Magnetic-field asymmetry of nonlinear transport in narrow channels with asymmetric hybrid confinement

Bettina Brandenstein-Köth, Lukas Worschech, and Alfred Forchel

Appl. Phys. Lett. 95, 062106 (2009); http://dx.doi.org/10.1063/1.3204462 (3 pages) | Cited 2 times

Online Publication Date: 12 August 2009

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The authors realized narrow constrictions in a two-dimensional electron gas (2DEG) with an in-plane asymmetry by means of a hybrid confinement. Unequal sidewalls of the constrictions were formed by combination of a single etched trench in a modulation doped GaAs/AlGaAs heterostructure which cuts through the 2DEG with an adjacent metallic top-gate, which depletes the underlying 2DEG. The two-terminal conductance was analyzed in magnetic fields applied perpendicular to the sample surface. In nonlinear transport, the conductance shows pronounced differences for an inversion of the magnetic field. The asymmetric conductance is related to scattering asymmetries caused by the different sidewalls in the asymmetric constriction.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.63.-b Electronic transport in nanoscale materials and structures

Generation of valley polarized current in bilayer graphene

D. S. L. Abergel and Tapash Chakraborty

Appl. Phys. Lett. 95, 062107 (2009); http://dx.doi.org/10.1063/1.3205117 (3 pages) | Cited 13 times

Online Publication Date: 14 August 2009

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We propose a device for the generation of valley polarized electronic current in bilayer graphene. By analyzing the response of this material to intense terahertz frequency light in the presence of a transverse electric field, we demonstrate that dynamical states are induced in the gapped energy region, and if the system parameters are properly tuned, these states exist only in one valley. The valley polarized states can then be used to filter an arbitrary electron current, so generating a valley polarized current.
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71.20.Tx Fullerenes and related materials; intercalation compounds
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.At Surface states, band structure, electron density of states

Effects of Ni cladding layers on suppression of Ag agglomeration in Ag-based Ohmic contacts on p-GaN

Jun Ho Son, Yang Hee Song, Hak Ki Yu, and Jong-Lam Lee

Appl. Phys. Lett. 95, 062108 (2009); http://dx.doi.org/10.1063/1.3206742 (3 pages) | Cited 6 times

Online Publication Date: 14 August 2009

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We investigate effects of Ni cladding layers on suppression of Ag agglomeration in Ag contacts on p-GaN using high-resolution x-ray diffraction. In the annealed Ag contact, Ag (100) grains disappear and agglomerate to form a selectively epitaxial growth of Ag (111). An ultrathin Ni contact layer (10 Å) below Ag film plays a role to epitaxially grow (111) Ag films on GaN, leading to the suppression of Ag agglomeration. A 20-Å-thick Ni overlayer effectively acts as a passivation layer to prevent the surface diffusion of Ag atoms during annealing, leading to high light reflectance and low contact resistivity.
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81.65.-b Surface treatments
73.40.Ns Metal-nonmetal contacts
68.55.A- Nucleation and growth
81.40.Gh Other heat and thermomechanical treatments
73.40.Cg Contact resistance, contact potential

Influence of N interstitials on the electronic properties of GaAsN alloys

Y. Jin, R. M. Jock, H. Cheng, Y. He, A. M. Mintarov, Y. Wang, C. Kurdak, J. L. Merz, and R. S. Goldman

Appl. Phys. Lett. 95, 062109 (2009); http://dx.doi.org/10.1063/1.3187915 (3 pages) | Cited 6 times

Online Publication Date: 14 August 2009

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We have used rapid thermal annealing to investigate the influence of N interstitials on the electronic properties of GaAsN alloys. Nuclear reaction analysis reveals an annealing-induced decrease in the interstitial N concentration, while the total N composition remains constant. Corresponding signatures for the reduced interstitial N concentration are apparent in Raman spectra. Following annealing, both the room-T carrier concentration, n, and the mobility increase. At higher measurement-Ts, a thermally activated increase in n suggests the presence of a trap near GaAsN conduction band edge with activation energy 85±15 meV. The annealing-induced increase in n suggests the association of the trap with interstitial N.
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.jj Interstitials
61.72.Cc Kinetics of defect formation and annealing
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Planar S-(S/F)-S Josephson junctions induced by the inverse proximity effect

O. Vávra, W. Pfaff, and Ch. Strunk

Appl. Phys. Lett. 95, 062501 (2009); http://dx.doi.org/10.1063/1.3200226 (3 pages) | Cited 3 times

Online Publication Date: 10 August 2009

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We present a utilization of the inverse proximity effect in superconductor-ferromagnet (S-F) bilayer to generate lateral Josephson junctions. The weak link is created by a Pd0.95Fe0.05 strip across a Nb bridge. Close to TC and in perpendicular magnetic field the junctions exhibit a modulation of the critical current IC(B) similar to a Fraunhofer interference pattern which proves the dc Josephson effect. The structure contains three weak links (two different areas) in series which result in the observation of two periods scalable with the areas penetrated by magnetic flux. Measurements of Shapiro steps prove the presence of the ac Josephson effect.
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74.50.+r Tunneling phenomena; Josephson effects
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Manipulation of the magnetic configuration of (Ga,Mn)As nanostructures

J. A. Haigh, M. Wang, A. W. Rushforth, E. Ahmad, K. W. Edmonds, R. P. Campion, C. T. Foxon, and B. L. Gallagher

Appl. Phys. Lett. 95, 062502 (2009); http://dx.doi.org/10.1063/1.3200242 (3 pages) | Cited 1 time

Online Publication Date: 10 August 2009

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We have studied the magnetic reversal of L-shaped nanostructures fabricated from (Ga,Mn)As. The strain relaxation due to the lithographic patterning results in each arm having a uniaxial magnetic anisotropy. Our analysis confirms that the magnetic reversal takes place via a combination of coherent rotation and domain wall propagation with the domain wall positioned at the corner of the device at intermediate stages of the magnetic hysteresis loops. The domain wall energy can be extracted from our analysis. Such devices have found implementation in studies of current induced domain wall motion and have the potential for application as nonvolatile memory elements.
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81.16.Rf Micro- and nanoscale pattern formation
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.60.Ch Domain walls and domain structure
62.25.-g Mechanical properties of nanoscale systems
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Pp Magnetic semiconductors

Accurate determination of the magnetic anisotropy in cluster-assembled nanostructures

Alexandre Tamion, Matthias Hillenkamp, Florent Tournus, Edgar Bonet, and Véronique Dupuis

Appl. Phys. Lett. 95, 062503 (2009); http://dx.doi.org/10.1063/1.3200950 (3 pages) | Cited 19 times

Online Publication Date: 10 August 2009

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The simultaneous triple adjustment of experimental magnetization curves under different conditions is shown to allow the unambiguous and consistent determination of both the magnetic particle size distribution and anisotropy for granular nanostructures of Co clusters embedded in protective matrices. The importance of interface effects resulting in magnetically dead layers is demonstrated.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
75.75.-c Magnetic properties of nanostructures

Double ferromagnetic resonance in nanowire arrays

Louis-Philippe Carignan, Vincent Boucher, Toshiro Kodera, Christophe Caloz, Arthur Yelon, and David Ménard

Appl. Phys. Lett. 95, 062504 (2009); http://dx.doi.org/10.1063/1.3194296 (3 pages) | Cited 9 times

Online Publication Date: 10 August 2009

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Microstrip line measurements are used to determine the frequency dependent microwave response of 40 nm diameter CoFeB ferromagnetic nanowire arrays, with external static applied field parallel to the nanowire axis. The ferromagnetic resonance (FMR) response of the wires is obtained for applied fields below and above magnetization saturation. For applied magnetic fields above saturation, a single FMR peak is observed, while below saturation, two sets of peaks are obtained. The two FMR peaks below saturation are associated with two magnetization populations, one for nanowires with upward magnetization and one with downward magnetization. A model based on a Maxwell–Garnett homogenization procedure has been established and used to predict the frequency response of the FMR peaks. There is good agreement between the model and experimental results.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
84.40.Az Waveguides, transmission lines, striplines
75.50.Bb Fe and its alloys

Density functional study on ferromagnetism in nitrogen-doped anatase TiO2

J. G. Tao, L. X. Guan, J. S. Pan, C. H. A. Huan, L. Wang, J. L. Kuo, Z. Zhang, J. W. Chai, and S. J. Wang

Appl. Phys. Lett. 95, 062505 (2009); http://dx.doi.org/10.1063/1.3204463 (3 pages) | Cited 27 times

Online Publication Date: 10 August 2009

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We report first principles calculations on the magnetism and electronic structures for nitrogen-doped anatase TiO2 (N:TiO2). Our calculations indicate that magnetic state is the ground state for N:TiO2 systems. An isolated N atom produces a total magnetic moment of 1.00μB and introduces spin-polarized 2p states in the band gap. The origin of the magnetic moments is the holes in N 2p π band of the N dopant. Several doping configurations studied suggest the existence of ferromagnetic coupling between N dopants. The ferromagnetism in N:TiO2 can be attributed to the hole-mediated double exchange through the strong p-p interaction between N and O.
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75.30.Cr Saturation moments and magnetic susceptibilities
72.25.Dc Spin polarized transport in semiconductors
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.30.Et Exchange and superexchange interactions

Microwave assisted magnetization reversal in single domain nanoelements

H. T. Nembach, H. Bauer, J. M. Shaw, M. L. Schneider, and T. J. Silva

Appl. Phys. Lett. 95, 062506 (2009); http://dx.doi.org/10.1063/1.3196556 (3 pages) | Cited 13 times

Online Publication Date: 11 August 2009

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We studied the microwave assisted magnetic reversal of 65×71 nm2 elliptical Ni80Fe20 nanomagnets. Hysteresis curves were measured by magneto-optical Kerr effect for a range of microwave frequencies and amplitudes. The coercive field Hc was reduced by 26% for an rf field of 0.08Hc when the microwave frequency coincided with the minimum of the experimentally determined ferromagnetic resonance frequency with varying dc field. The experimental results for the fractional reduction in Hc with rf field amplitude are in good agreement with numerical simulations for an array of interacting macrospins with a physically realistic shape anisotropy distribution.
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75.60.Jk Magnetization reversal mechanisms
78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

In situ fabrication of cobalt-doped SrFe2As2 thin films by using pulsed laser deposition with excimer laser

Eun-Mi Choi, Soon-Gil Jung, Nam Hoon Lee, Young-Seung Kwon, Won Nam Kang, Dong Ho Kim, Myung-Hwa Jung, Sung-Ik Lee, and Liling Sun

Appl. Phys. Lett. 95, 062507 (2009); http://dx.doi.org/10.1063/1.3204457 (3 pages) | Cited 17 times

Online Publication Date: 12 August 2009

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The remarkably high superconducting transition temperature and upper critical field of iron (Fe)-based layered superconductors, despite ferromagnetic material base, open the prospect for superconducting electronics. However, success in superconducting electronics has been limited because of difficulties in fabricating high-quality thin films. We report the growth of high-quality c-axis-oriented cobalt (Co)-doped SrFe2As2 thin films with bulk superconductivity by using an in situ pulsed laser deposition technique with a 248 nm wavelength KrF excimer laser and an arsenic (As)-rich phase target. The temperature and field dependences of the magnetization showing strong diamagnetism and transport critical current density with superior Jc-H performance are reported. These results provide necessary information for practical applications of Fe-based superconductors.
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81.15.Fg Pulsed laser ablation deposition
74.78.-w Superconducting films and low-dimensional structures
74.25.Op Mixed states, critical fields, and surface sheaths
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.25.Sv Critical currents
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
74.25.Ha Magnetic properties including vortex structures and related phenomena

Giant magnetic anisotropy changes in Sr2CrReO6 thin films on BaTiO3

F. D. Czeschka, S. Geprägs, M. Opel, S. T. B. Goennenwein, and R. Gross

Appl. Phys. Lett. 95, 062508 (2009); http://dx.doi.org/10.1063/1.3200236 (3 pages) | Cited 6 times

Online Publication Date: 13 August 2009

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The integration of ferromagnetic and ferroelectric materials into hybrid heterostructures yields multifunctional systems with improved or novel functionality. We here report on the structural, electronic, and magnetic properties of the ferromagnetic double perovskite Sr2CrReO6, grown as epitaxial thin film onto ferroelectric BaTiO3. As a function of temperature, the crystal-structure of BaTiO3 undergoes phase transitions, which induce qualitative changes in the magnetic anisotropy of the ferromagnet. We observe abrupt changes in the coercive field of up to 1.2 T along with resistance changes of up to 6.5%. These results are attributed to the high sensitivity of the double perovskites to mechanical deformation.
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75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
77.80.B- Phase transitions and Curie point
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
73.61.Ng Insulators
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.40.Lm Deformation, plasticity, and creep
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Tunable magnetic and transport properties of single crystalline (Co, Ga)-codoped ZnO films

Zhonglin Lu, Hua-Shu Hsu, Yonhua Tzeng, Fengming Zhang, Youwei Du, and Jung-Chun-Andrew Huang

Appl. Phys. Lett. 95, 062509 (2009); http://dx.doi.org/10.1063/1.3204016 (3 pages) | Cited 2 times

Online Publication Date: 13 August 2009

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A series of metallic (Co, Ga)-codoped ZnO single crystalline films have been grown by molecular beam epitaxy. All of the films exhibit metallic conducting behavior and high free carrier concentrations. Besides room temperature ferromagnetism, the anomalous Hall effect due to spin-orbit interaction was also found. Both the saturation magnetization and anomalous Hall effect can be tuned by the carrier concentration or conductivity, revealing that the ferromagnetism is carrier mediated in (Co, Ga)-codoped ZnO films. Our experimental observations are consistent with the recent theoretical description of carrier mediated magnetism in Co doped ZnO.
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72.20.My Galvanomagnetic and other magnetotransport effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.Ak Magnetic properties of monolayers and thin films
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
75.50.Pp Magnetic semiconductors
68.55.ag Semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Josephson effect between electron-doped and hole-doped iron pnictide single crystals

Xiaohang Zhang, Shanta R. Saha, Nicholas P. Butch, Kevin Kirshenbaum, Johnpierre Paglione, Richard L. Greene, Yong Liu, Liqin Yan, Yoon Seok Oh, Kee Hoon Kim, and Ichiro Takeuchi

Appl. Phys. Lett. 95, 062510 (2009); http://dx.doi.org/10.1063/1.3205123 (3 pages) | Cited 11 times

Online Publication Date: 14 August 2009

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We have observed the Josephson effect in junctions formed between single crystals of SrFe1.74Co0.26As2 and Ba0.23K0.77Fe2As2. The ac Josephson effect was observed under microwave irradiation in the I-V characteristics. By applying an in-plane magnetic field, the critical current is completely modulated and shows a relatively symmetric diffraction pattern consistent with the intermediate junction limit. The observation of the Josephson effect in the p-n bicrystal structure not only has significant implications for designing phase-sensitive junctions to probe the pairing symmetry of iron pnictide superconductors, but also represents an important step in developing all iron pnictide devices for applications.
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74.50.+r Tunneling phenomena; Josephson effects
72.30.+q High-frequency effects; plasma effects
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
74.25.Sv Critical currents
74.25.F- Transport properties

Electrical detection of microwave assisted magnetization switching in a Permalloy microstrip

Xiaolong Fan, Y. S. Gui, A. Wirthmann, G. Williams, Desheng Xue, and C.-M. Hu

Appl. Phys. Lett. 95, 062511 (2009); http://dx.doi.org/10.1063/1.3200239 (3 pages) | Cited 8 times

Online Publication Date: 14 August 2009

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Microwave assisted magnetization switching has been investigated in a nonelliptic Permalloy microstrip, using radio frequency magnetic fields h applied in-plane perpendicular to the long axis of the strip. In low power excitations, Hs decreases almost linearly with increasing h; this can be qualitatively understood by introducing an susceptibility χyy that links the dynamic magnetization inside the microstip to the h field outside the microstip. However, at high frequencies, Hs no longer decrease with increasing h when this latter field exceeds a critical value. We suppose such “saturation” effects could attribute to the nonlinear ferromagnetic resonance caused by high power excitations.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
84.40.Dc Microwave circuits
75.50.Bb Fe and its alloys
84.40.Az Waveguides, transmission lines, striplines
75.30.Cr Saturation moments and magnetic susceptibilities
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

An investigation of the magnetic state dependent low frequency noise in magnetic tunnel junctions

Feng Guo, Greg McKusky, and E. Dan Dahlberg

Appl. Phys. Lett. 95, 062512 (2009); http://dx.doi.org/10.1063/1.3205476 (3 pages) | Cited 5 times

Online Publication Date: 14 August 2009

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The low frequency noise in magnetic tunnel junctions was studied as a function of applied magnetic field. In magnetic states where the magnetization is reversing, the measurement indicates a 1/f2 spectrum whereas at all other applied fields a 1/f spectrum is observed. The 1/f2 spectra are found to be an artifact of the magnetic after effect. Without the artificial influence of the magnetic after effect, only 1/f spectra are observed.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.60.Lr Magnetic aftereffects

Strong anisotropy of magnetization and sign reversion of ordinary Hall coefficient in single crystal Ge1−xMnx magnetic semiconductor films

J. X. Deng, Y. F. Tian, S. M. He, H. L. Bai, T. S. Xu, S. S. Yan, Y. Y. Dai, Y. X. Chen, G. L. Liu, and L. M. Mei

Appl. Phys. Lett. 95, 062513 (2009); http://dx.doi.org/10.1063/1.3206664 (3 pages) | Cited 8 times

Online Publication Date: 14 August 2009

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Epitaxial single-crystal Ge1−xMnx ferromagnetic-semiconductor films were fabricated on Ge(001) substrates by molecular beam epitaxy. All the samples are ferromagnetic and have strong magnetic anisotropy indicated by different magnetization in plane and out of plane. The electrical transport of the films obeys Efros variable range hopping law in the low temperature range. Interestingly, a negative coefficient of the ordinary Hall effect of p-type carriers was found in the variable range hopping at low temperature. Anomalous Hall effect in Ge0.949Mn0.051 film was observed below the Curie temperature, indicating the carrier-mediated intrinsic ferromagnetism.
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75.30.Gw Magnetic anisotropy
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.Ak Magnetic properties of monolayers and thin films
68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors
73.61.Le Other inorganic semiconductors
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Nanoscale oxygen octahedral tilting in 0.90(Bi1/2Na1/2)TiO3–0.05(Bi1/2K1/2)TiO3–0.05BaTiO3 lead-free perovskite piezoelectric ceramics

Cheuk W. Tai (戴卓偉) and Y. Lereah

Appl. Phys. Lett. 95, 062901 (2009); http://dx.doi.org/10.1063/1.3193544 (3 pages) | Cited 19 times

Online Publication Date: 10 August 2009

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The oxygen octahedral tilted domains in 0.90(Bi1/2Na1/2)TiO3–0.5(Bi1/2K1/2)TiO3–0.5BaTiO3 lead-free perovskite piezoelectric ceramic have been studied by transmission electron microscopy (TEM). Selected-area electron diffraction patterns shows the ½ooo and ½ooe reflections, indicating the presence of antiphase (a−a−a−) and in-phase (aoaoc+) octahedral tilting, respectively. The morphology and distributions of these tilted domains are shown in the centered dark-field images. Further, the Bragg-filtered high-resolution TEM image reveals that the size of the in-phase tilted domains varies from 1 to 8 nm across. The ceramic contains the mixture of nontilted and variants of the antiphase and in-phase tilted domains.
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77.65.Bn Piezoelectric and electrostrictive constants
77.80.Dj Domain structure; hysteresis
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization

Molecular beam epitaxy of SrTiO3 on Si (001): Early stages of the growth and strain relaxation

G. Niu, G. Saint-Girons, B. Vilquin, G. Delhaye, J.-L. Maurice, C. Botella, Y. Robach, and G. Hollinger

Appl. Phys. Lett. 95, 062902 (2009); http://dx.doi.org/10.1063/1.3193548 (3 pages) | Cited 17 times

Online Publication Date: 10 August 2009

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The molecular beam epitaxy of SrTiO3 (STO) layers on Si (001) is studied, focusing on the early stages of the growth and on the strain relaxation process. Evidence is given that even for optimized growth conditions, STO grows initially amorphous on silicon and recrystallizes, leading to the formation of an atomically abrupt heterointerface with silicon. Just after recrystallization, STO is partially strained. Further increase in its thickness leads to the onset of a progressive plastic relaxation mechanism. STO recovers its bulk lattice parameter for thicknesses of the order of 30 ML.
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68.55.at Other materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Dielectric response of high permittivity polymer ceramic composite with low loss tangent

G. Subodh, V. Deepu, P. Mohanan, and M. T. Sebastian

Appl. Phys. Lett. 95, 062903 (2009); http://dx.doi.org/10.1063/1.3200244 (3 pages) | Cited 13 times

Online Publication Date: 10 August 2009

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The present communication investigates the dielectric response of the Sr9Ce2Ti12O36 ceramics loaded high density polyethylene and epoxy resin. Sr9Ce2Ti12O36 ceramic filled polyethylene and epoxy composites were prepared using hot blending and mechanical mixing, respectively. 40 vol % ceramic loaded polyethylene has relative permittivity of 12.1 and loss tangent of 0.004 at 8 GHz, whereas the corresponding composite using epoxy as matrix has permittivity and loss tangent of 14.1 and 0.022, respectively. The effective medium theory fits relatively well for the observed permittivity of these composites.
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77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Mh Cermets, ceramic and refractory composites
81.05.Qk Reinforced polymers and polymer-based composites

High dielectric permittivity in semiconducting Pr0.6Ca0.4MnO3 filled polyvinylidene fluoride nanocomposites with low percolation threshold

K. Devi Chandrasekhar, A. Venimadhav, and A. K. Das

Appl. Phys. Lett. 95, 062904 (2009); http://dx.doi.org/10.1063/1.3196550 (3 pages) | Cited 6 times

Online Publication Date: 10 August 2009

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Semiconducting Pr0.6Ca0.4MnO3 nanoparticles with width of ∼ 50 nm and length ∼ 80–150 nm were prepared by sol-gel method. The dielectric behavior of Pr0.6Ca0.4MnO3, polyvinylidene fluoride composites was investigated by varying the Pr0.6Ca0.4MnO3 volume fraction and frequency. The percolation threshold of the composites was found to be 0.1 and an enhanced effective dielectric permittivity of ∼ 700 with low dielectric loss of ∼ 0.3 at 103 Hz near the percolation threshold was observed. The low percolation threshold was attributed to the nanosize and nonspherical shape of the filler particles, and the enhanced dielectric properties have been explained by using boundary layer capacitance effect and percolation theory.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.-b Nanoscale materials and structures: fabrication and characterization
77.22.Gm Dielectric loss and relaxation
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
73.63.-b Electronic transport in nanoscale materials and structures
77.22.Ch Permittivity (dielectric function)

Non-180° domains in LiTaO3 thin films deposited by metal organic chemical vapor deposition

Z. B. He, N. Setter, T. Ono, and K. Shinozaki

Appl. Phys. Lett. 95, 062905 (2009); http://dx.doi.org/10.1063/1.3204451 (3 pages) | Cited 2 times

Online Publication Date: 13 August 2009

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Epitaxial lithium tantalate (LiTaO3) thin films were grown on the hexagonal plane of sapphire substrates by metal organic chemical vapor deposition. Two crystallographic variants, related to each other by 180° rotation around the c axis, as well as non-180° domains were determined by transmission electron microscopy from cross-sectional samples of these films. A structural model for the non-180° domain is proposed and the possible formation mechanisms are discussed.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Og High-resolution transmission electron microscopy (HRTEM)
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.aj Insulators

The effect of SrTiO3 substrate orientation on the surface morphology and ferroelectric properties of pulsed laser deposited NaNbO3 films

Seiji Yamazoe, Hiroyuki Sakurai, Masaki Fukada, Hideaki Adachi, and Takahiro Wada

Appl. Phys. Lett. 95, 062906 (2009); http://dx.doi.org/10.1063/1.3205103 (3 pages) | Cited 11 times

Online Publication Date: 14 August 2009

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Orientated NaNbO3 (NN) films were grown on SrRuO3/(001)SrTiO3 [SRO/(001)STO], SRO/(110)STO, and SRO/(111)STO substrates by pulsed laser deposition. Scanning electron microscopy images showed that the surface morphologies of the NN/SRO/(001)STO, NN/SRO/(110)STO, and NN/SRO/(111)STO took the form of a stepped structure, a striped pattern, and trigonal pyramidal-like structures, respectively. The dielectric and ferroelectric properties of the films were characterized. The NN/SRO/(110)STO film showed the lowest relative dielectric constant and the largest remanent polarization of 30.8 μC/cm2 among all films. These were interpreted as being due to the orientation direction of the NN film grown on (110)STO being parallel to the polarization direction of NN.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Fg Pulsed laser ablation deposition

On the strain coupling across vertical interfaces of switchable BiFeO3–CoFe2O4 multiferroic nanostructures

N. Dix, R. Muralidharan, J. Guyonnet, B. Warot-Fonrose, M. Varela, P. Paruch, F. Sánchez, and J. Fontcuberta

Appl. Phys. Lett. 95, 062907 (2009); http://dx.doi.org/10.1063/1.3204464 (3 pages) | Cited 12 times

Online Publication Date: 14 August 2009

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In magnetoelectrically coupled CoFe2O4–BiFeO3 nanostructures vertical and lateral lattice parameters of both phases are determined. We find that the in-plane lattice parameter of CoFe2O4 is fully relaxed whereas it presents compressive strain along the out-of-plane direction. Although the CoFe2O4–BiFeO3 interface is semicoherent, CoFe2O4 out-of-plane lattice strain is not relaxed after selective removal of the matrix and thus it is of nonelastic origin. In spite of the absence of elastic residual strain caused by CoFe2O4–BiFeO3 interfaces, the two phases are mechanically coupled as demonstrated by the electrical switching of the magnetization.
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68.35.Gy Mechanical properties; surface strains
68.35.Ct Interface structure and roughness
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.46.-w Structure of nanoscale materials

Metal-oxide-semiconductor capacitors with ZrO2 dielectrics grown on In0.53Ga0.47As by chemical beam deposition

Roman Engel-Herbert, Yoontae Hwang, Joël Cagnon, and Susanne Stemmer

Appl. Phys. Lett. 95, 062908 (2009); http://dx.doi.org/10.1063/1.3204465 (3 pages) | Cited 22 times

Online Publication Date: 14 August 2009

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Zirconium oxide films were grown by chemical beam deposition with zirconium tert-butoxide as the source on (2×4) reconstructed, n-type In0.53Ga0.47As surfaces obtained after As decapping. Optimized growth conditions yielded ZrO2/In0.53Ga0.47As interfaces that were free of second phases. Capacitance-voltage (CV) measurements with different top electrodes showed a frequency dispersion of less than 2% per decade in accumulation. The accumulation capacitance and horizontal position of the CV curve were independent of temperature, while the inversion capacitance was strongly temperature dependent. Flat band voltages correlated with the work function of the metal electrode.
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84.32.Tt Capacitors
82.45.Un Dielectric materials in electrochemistry
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