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18 May 2009

Volume 94, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 203301 (2009); http://dx.doi.org/10.1063/1.3133902 (3 pages)

Zihong Liu, Joon Hak Oh, Mark E. Roberts, Peng Wei, Bipul C. Paul, Masaki Okajima, Yoshio Nishi, and Zhenan Bao
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Isotropic transport in an oligothiophene derivative for single-crystal field-effect transistor applications

Colin Reese, Mark E. Roberts, Sean R. Parkin, and Zhenan Bao

Appl. Phys. Lett. 94, 202101 (2009); http://dx.doi.org/10.1063/1.3129162 (3 pages) | Cited 4 times

Online Publication Date: 18 May 2009

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Single-crystal organic semiconductors have proven invaluable tools in the exploration of charge transport in molecular materials. We employ the elastomeric, photolithographically patterned single-crystal field-effect transistor in the study of an alpha-substituted oligothiophene. The terminal units specify a symmetric layered motif, while allowing the oligothiophene cores to pack closely. Angle-resolved measurements of the field-effect mobility reflect the symmetric edge/face interactions and isotropic mobility. These measurements are supported by electronic structure calculations that show nearly equivalent intermolecular interactions along cell diagonals. These results reveal that the transport is diffusive and a minimum of fourfold symmetry is required for in-plane mobility isotropy.
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72.20.Fr Low-field transport and mobility; piezoresistance
66.30.-h Diffusion in solids
85.30.Tv Field effect devices

Pre-edges in oxygen (1s) x-ray absorption spectra: A spectral indicator for electron hole depletion and transport blocking in iron perovskites

Artur Braun, Defne Bayraktar, Selma Erat, Ashley S. Harvey, Daniel Beckel, John A. Purton, Peter Holtappels, Ludwig J. Gauckler, and Thomas Graule

Appl. Phys. Lett. 94, 202102 (2009); http://dx.doi.org/10.1063/1.3122926 (3 pages) | Cited 8 times

Online Publication Date: 19 May 2009

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The eg↑/(t2g↓+eg↓) band ratio in cation-substituted La–Fe oxides is identified in O (1s) x-ray absorption spectra as a linear spectral indicator for conducting electron holes. The t2g↓ and eg↓ bands act as a conductivity inhibitor by ferromagnetic double exchange coupling on the eg↑ electron. Disorder induced by substitution appears to modulate the hole conduction such that an exponential relation is found between the conductivity and the eg↑/(t2g↓+eg↓) ratio and hole concentration. The quantitative correlation of conductivity and x-ray absorption spectra from heterovalent-substituted LaFeO3 lets substitution-driven metal insulator transitions appear in a new light.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.70.Dm X-ray absorption spectra
75.30.Et Exchange and superexchange interactions
71.30.+h Metal-insulator transitions and other electronic transitions
72.80.Sk Insulators
75.50.Dd Nonmetallic ferromagnetic materials

A wide-band-gap p-type thermoelectric material based on quaternary chalcogenides of Cu2ZnSnQ4 (Q = S,Se)

Min-Ling Liu, Fu-Qiang Huang, Li-Dong Chen, and I-Wei Chen

Appl. Phys. Lett. 94, 202103 (2009); http://dx.doi.org/10.1063/1.3130718 (3 pages) | Cited 30 times

Online Publication Date: 19 May 2009

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Chalcopyritelike quaternary chalcogenides, Cu2ZnSnQ4 (Q = S,Se), were investigated as an alternative class of wide-band-gap p-type thermoelectric materials. Their distorted diamondlike structure and quaternary compositions are beneficial to lowering lattice thermal conductivities. Meanwhile, partial substitution of Cu for Zn creates more charge carriers and conducting pathways via the CuQ4 network, enhancing electrical conductivity. The power factor and the figure of merit (ZT) increase with the temperature, making these materials suitable for high temperature applications. For Cu2.1Zn0.9SnQ4, ZT reaches about 0.4 at 700 K, rising to 0.9 at 860 K.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
61.72.up Other materials

Fabrication of compositional graded Si1−xGex layers by using thermal oxidation

J. H. Jang, S. Y. Son, Wantae Lim, M. S. Phen, K. Siebein, S. J. Pearton, and V. Craciun

Appl. Phys. Lett. 94, 202104 (2009); http://dx.doi.org/10.1063/1.3139070 (3 pages) | Cited 4 times

Online Publication Date: 19 May 2009

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Compositional graded and highly relaxed Si1−xGex layers have been fabricated by using thermal oxidation at high temperature. It was found that the behavior of Ge atoms during thermal oxidation was significantly dependent of the oxidation temperature. The Ge accumulation below the oxide occurred at 800 and 900 °C due to a large difference of the heat formation of GeO2 and SiO2. However, Si1−xGex layers oxidized in 1000 °C did not show any Ge accumulation because Ge diffusion efficiently occurred. The compositional graded Si1−xGex layers fabricated by thermal oxidation can be used as virtual substrates for the strained-Si and relaxed-SiGe applications.
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81.65.Mq Oxidation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
66.30.-h Diffusion in solids

Effect of nanoparticle scattering on thermoelectric power factor

Mona Zebarjadi, Keivan Esfarjani, Ali Shakouri, Je-Hyeong Bahk, Zhixi Bian, Gehong Zeng, John Bowers, Hong Lu, Joshua Zide, and Art Gossard

Appl. Phys. Lett. 94, 202105 (2009); http://dx.doi.org/10.1063/1.3132057 (3 pages) | Cited 36 times

Online Publication Date: 20 May 2009

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The effect of nanoparticles on the thermoelectric power factor is investigated using the relaxation time approximation. The partial-wave technique is used for calculating the nanoparticle scattering cross section exactly. We validate our model by comparing its results to the experimental data obtained for ErAs:InGaAlAs samples. We use the theory to maximize the power factor with respect to nanoparticle and electron concentrations as well as the barrier height. We found that at the optimum of the power factor, the electron concentration is usually higher in the sample with nanoparticles, implying that Seebeck is usually unchanged and conductivity is increased.
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73.50.Lw Thermoelectric effects
72.20.Dp General theory, scattering mechanisms
73.63.-b Electronic transport in nanoscale materials and structures

Understanding the observation of large electrical conductivity in liquid crystal-carbon nanotube composites

V. Jayalakshmi and S. Krishna Prasad

Appl. Phys. Lett. 94, 202106 (2009); http://dx.doi.org/10.1063/1.3133352 (3 pages) | Cited 6 times

Online Publication Date: 20 May 2009

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We report the electrical conductivity and dielectric constant measurements in composites of single-walled carbon nanotubes (CNTs) with nematic liquid crystals, employing electrical and magnetic fields as reorienting fields. Our studies demonstrate that the large magnitude of enhancement in the electrical conductivity reported in voltage-driven reorientation measurements is not due to the inherent property of CNTs, and that dielectric breakdown and local heating effects play an important role. The calculated magnitude of the local heating effect is in agreement with the experimental observation including the nematic-isotropic transition caused by such Joule heating.
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73.63.Fg Nanotubes
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
77.22.Ch Permittivity (dielectric function)
77.22.Jp Dielectric breakdown and space-charge effects

Resistive switching in nanostructured thin films

H. Silva, H. L. Gomes, Yu. G. Pogorelov, P. Stallinga, D. M. de Leeuw, J. P. Araujo, J. B. Sousa, S. C. J. Meskers, G. Kakazei, S. Cardoso, and P. P. Freitas

Appl. Phys. Lett. 94, 202107 (2009); http://dx.doi.org/10.1063/1.3134484 (3 pages) | Cited 8 times

Online Publication Date: 20 May 2009

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Planar capacitor structures based on granular films composed of nanometric ferromagnetic grains embedded in an insulating Al2O3 matrix can switch between a high-conductance and a low-conductance state. The switching properties are induced by a forming process. The ON/OFF resistance ratio is as high as 104 under an electrical field of only 15 kV/m. This resistive switching is accompanied by a capacitive switching between two well-defined voltage-independent states, a behavior that is not readily explained by the filamentary type of conduction.
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73.63.Bd Nanocrystalline materials

Ga2O3(Gd2O3) on Ge without interfacial layers: Energy-band parameters and metal oxide semiconductor devices

L. K. Chu, T. D. Lin, M. L. Huang, R. L. Chu, C. C. Chang, J. Kwo, and M. Hong

Appl. Phys. Lett. 94, 202108 (2009); http://dx.doi.org/10.1063/1.3139772 (3 pages) | Cited 8 times

Online Publication Date: 20 May 2009

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Ga2O3(Gd2O3) (GGO) directly deposited on Ge substrate in ultrahigh vacuum, without a passivation layer such as GeOxNy or Si, has demonstrated excellent electrical performances and thermodynamic stability. Energy-band parameters of GGO/Ge have been determined by in situ x-ray photoelectron spectroscopy in conjunction with reflection electron energy loss spectroscopy and current transport of Fowler–Nordheim tunneling. A conduction-band offset and a valence-band offset of ∼ 2.3 and ∼ 2.42 eV, respectively, have been obtained. Moreover, self-aligned Ge pMOSFETs of 1-μm-gate length using Al2O3/GGO as the gate dielectrics have shown a high drain current and a peak transconductance of 252 mA/mm, and 143 mS/mm, respectively.
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85.30.Tv Field effect devices
73.20.At Surface states, band structure, electron density of states
73.40.Gk Tunneling
65.40.G- Other thermodynamical quantities
79.60.Jv Interfaces; heterostructures; nanostructures
79.20.Uv Electron energy loss spectroscopy

Measuring spin diffusion of electrons in bulk n-GaAs using circularly dichromatic absorption difference spectroscopy of spin gratings

Hua-Liang Yu, Xiu-Min Zhang, Peng-Fei Wang, Hai-Qiao Ni, Zhi-Chuan Niu, and Tianshu Lai

Appl. Phys. Lett. 94, 202109 (2009); http://dx.doi.org/10.1063/1.3141483 (3 pages) | Cited 2 times

Online Publication Date: 21 May 2009

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Circular dichromatic absorption difference spectroscopy is developed to measure the spin diffusion dynamics of electrons in bulk n-GaAs. This spectroscopy has higher detection sensitivity over homodyne detection of spin-grating-diffracted signal. A model to describe circular dichromatic absorption difference signal is derived and used to fit experimental signal to retrieve decaying rate of spin gratings. A spin diffusion constant of Ds = 201±25 cm2/s for bulk n-GaAs has been measured at room temperature using this technique and is close to electron diffusion constant (Dc), which is much different from the case in GaAs quantum wells where Ds is markedly less than Dc.
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72.25.Dc Spin polarized transport in semiconductors
72.80.Ey III-V and II-VI semiconductors
66.30.H- Self-diffusion and ionic conduction in nonmetals
78.20.Fm Birefringence

Energy barriers at interfaces between (100) InxGa1−xAs (0 ≤ x ≤ 0.53) and atomic-layer deposited Al2O3 and HfO2

V. V. Afanas’ev, A. Stesmans, G. Brammertz, A. Delabie, S. Sionke, A. O’Mahony, I. M. Povey, M. E. Pemble, E. O’Connor, P. K. Hurley, and S. B. Newcomb

Appl. Phys. Lett. 94, 202110 (2009); http://dx.doi.org/10.1063/1.3137187 (3 pages) | Cited 11 times

Online Publication Date: 21 May 2009

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The electron energy band alignment at interfaces of InxGa1−xAs (0 ≤ x ≤ 0.53) with atomic-layer deposited insulators Al2O3 and HfO2 is characterized using internal photoemission and photoconductivity experiments. The energy of the InxGa1−xAs valence band top is found to be only marginally influenced by the semiconductor composition. This result suggests that the known bandgap narrowing from 1.42 to 0.75 eV when the In content increases from 0 to 0.53 occurs mostly through downshift of the semiconductor conduction band bottom. It finds support from both electron and hole photoemission data. Similarly to the GaAs case, electron states originating from the interfacial oxidation of InxGa1−xAs lead to reduction in the electron barrier at the semiconductor/oxide interface.
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71.20.Nr Semiconductor compounds
73.61.Ey III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
79.60.Ht Disordered structures
79.60.Jv Interfaces; heterostructures; nanostructures
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Transition into a gapless state and concentration anomalies in the properties of Bi1−xSbx solid solutions

E. I. Rogacheva, A. A. Drozdova, O. N. Nashchekina, M. S. Dresselhaus, and G. Dresselhaus

Appl. Phys. Lett. 94, 202111 (2009); http://dx.doi.org/10.1063/1.3139076 (3 pages) | Cited 2 times

Online Publication Date: 21 May 2009

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For Bi1−xSbx solid solutions (x = 0.01–0.05), the dependences of the electrical conductivity, Hall coefficient, charge carrier mobility, magnetoresistance, Seebeck coefficient, and microhardness on the Sb concentration have been obtained in the temperature range of 77–300 K. In the isotherms of these properties, distinct extrema or inflection points have been observed in the range of x = 0.025–0.035. The presence of these concentration anomalies is attributed to the critical phenomena, which accompany the transition into a gapless state under increasing Sb concentration.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
71.30.+h Metal-insulator transitions and other electronic transitions
72.15.Jf Thermoelectric and thermomagnetic effects
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Origin of flatband voltage shift and unusual minority carrier generation in thermally grown GeO2/Ge metal-oxide-semiconductor devices

Takuji Hosoi, Katsuhiro Kutsuki, Gaku Okamoto, Marina Saito, Takayoshi Shimura, and Heiji Watanabe

Appl. Phys. Lett. 94, 202112 (2009); http://dx.doi.org/10.1063/1.3143627 (3 pages) | Cited 27 times

Online Publication Date: 22 May 2009

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Improvement in electrical properties of thermally grown GeO2/Ge metal-oxide-semiconductor (MOS) capacitors, such as significantly reduced flatband voltage (VFB) shift, small hysteresis, and minimized minority carrier response in capacitance-voltage (C-V) characteristics, has been demonstrated by in situ low temperature vacuum annealing prior to gate electrode deposition. Thermal desorption analysis has revealed that not only water but also hydrocarbons are easily infiltrated into GeO2 layers during air exposure and desorbed at around 300 °C, indicating that organic molecules within GeO2/Ge MOS structures are possible origins of electrical defects. The inversion capacitance, indicative of minority carrier generation, increases with air exposure time for Au/GeO2/Ge MOS capacitors, while maintaining an interface state density (Dit) of about a few 1011 cm−2 eV−1. Unusual increase in inversion capacitance was found to be suppressed by Al2O3 capping (Au/Al2O3/GeO2/Ge structures). This suggests that electrical defects induced outside the Au electrode by infiltrated molecules may enhance the minority carrier generation, and thus acting as a minority carrier source just like MOS field-effect transistors.
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84.32.Tt Capacitors
61.72.Cc Kinetics of defect formation and annealing
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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Pattern induced phase transition of vortex motion in high-Tc films

R. Wördenweber, E. Hollmann, J. Schubert, R. Kutzner, and Ajay Kumar Ghosh

Appl. Phys. Lett. 94, 202501 (2009); http://dx.doi.org/10.1063/1.3139077 (3 pages) | Cited 2 times

Online Publication Date: 18 May 2009

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A micropattern induced transition in the mechanism of vortex motion and vortex mobility is demonstrated for high-Tc films. The competition between the anomalous Hall effect and the guidance of vortices by rows of microholes (antidots) leads to a sudden change in the direction of vortex motion that is accompanied by a change of the critical current density and microwave losses. The latter demonstrates the difference in vortex mobility in the different phases of vortex motion in between and within the rows of antidots.
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74.78.-w Superconducting films and low-dimensional structures
72.15.Gd Galvanomagnetic and other magnetotransport effects
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Spin polarization of Fe4N thin films determined by point-contact Andreev reflection

A. Narahara, K. Ito, T. Suemasu, Y. K. Takahashi, A. Ranajikanth, and K. Hono

Appl. Phys. Lett. 94, 202502 (2009); http://dx.doi.org/10.1063/1.3140459 (3 pages) | Cited 12 times

Online Publication Date: 18 May 2009

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The spin polarization of (100)-oriented γ′-Fe4N layers grown on MgO(001) substrates by molecular beam epitaxy was deduced from point contact Andreev reflection measurements, and the value was compared with that of α-Fe. The spin polarization (P) for γ′-Fe4N is approximately 0.59 at 7.8 K. This value is distinctly larger than that for α-Fe (P = 0.49 at 7.8 K) measured with an identical setting. The mechanism of enhanced spin polarization in γ′-Fe4N is discussed.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth

Surface and core magnetic anisotropy in maghemite nanoparticles determined by pressure experiments

Y. Komorida, M. Mito, H. Deguchi, S. Takagi, A. Millán, N. J. O. Silva, and F. Palacio

Appl. Phys. Lett. 94, 202503 (2009); http://dx.doi.org/10.1063/1.3131782 (3 pages) | Cited 9 times

Online Publication Date: 19 May 2009

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In magnetic nanoparticles, anisotropy energy has extra contributions compared to that of the bulk counterparts, being the most relevant surface anisotropy. Here we use pressure to separate core from surface anisotropy in one system of maghemite nanoparticles dispersed in a polymer. The core anisotropy is Kcore = 7.7×105 erg/cm3 while the surface anisotropy is KS = 4.2×10−2 erg/cm2. This in-one-sample separation is possible due to changes in structurally ordered and disordered ratio, which induce changes in the average magnetic anisotropy energy.
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75.30.Gw Magnetic anisotropy
75.70.Rf Surface magnetism
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Tt Fine-particle systems; nanocrystalline materials

Dynamics of single vortices in grain boundaries: I-V characteristics on the femtovolt scale

B. Kalisky, J. R. Kirtley, E. A. Nowadnick, R. B. Dinner, E. Zeldov, Ariando, S. Wenderich, H. Hilgenkamp, D. M. Feldmann, and K. A. Moler

Appl. Phys. Lett. 94, 202504 (2009); http://dx.doi.org/10.1063/1.3137164 (3 pages) | Cited 3 times

Online Publication Date: 19 May 2009

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We employed a scanning Hall probe microscope to detect the hopping of individual vortices between pinning sites along grain boundaries in YBa2Cu3O6+δ thin films in the presence of an applied current. Detecting the motion of individual vortices allowed us to probe the current-voltage (I-V) characteristics of the grain boundary with voltage sensitivity below a femtovolt. We find a very sharp onset of dissipation with V∝In with an unprecedented high exponent of n ≈ 290 that shows essentially no dependence on temperature or grain boundary angle. Our data have no straightforward explanation within the existing grain boundary transport models.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties

Nonreciprocal microwave devices based on magnetic nanowires

Bijoy K. Kuanr, V. Veerakumar, Ryan Marson, Sanjay R. Mishra, R. E. Camley, and Z. Celinski

Appl. Phys. Lett. 94, 202505 (2009); http://dx.doi.org/10.1063/1.3124657 (3 pages) | Cited 15 times

Online Publication Date: 20 May 2009

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We use magnetic nanowires in an alumina matrix as the active element in microwave nonreciprocal resonance isolators. The design is related to waveguide E-plane isolators but is planar and much smaller than typical waveguide isolators. There is a nonreciprocal attenuation of the wave in forward and reverse directions. The isolation is about 6 dB/cm at 23 GHz. The bandwidth of the device is relatively large (5–7 GHz) in comparison to ferrite-based devices. The central frequency of the device can be tuned with the application of magnetic field.
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84.40.Az Waveguides, transmission lines, striplines
85.70.-w Magnetic devices

Low frequency magnetoresistive noise in spin-valve structures

A. Ozbay, A. Gokce, T. Flanagan, R. A. Stearrett, E. R. Nowak, and C. Nordman

Appl. Phys. Lett. 94, 202506 (2009); http://dx.doi.org/10.1063/1.3139067 (3 pages) | Cited 19 times

Online Publication Date: 20 May 2009

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We report on resistance noise in spin-valve structures that is due to reconfigurations in domain structure of the magnetic layers. 1/f noise from the free layer and pinned layer is evident and its magnitude is in good agreement with predictions from the fluctuation dissipation relation using the imaginary (dissipative) component of the measured resistance susceptibility. In addition, we find that the imaginary component is dependent on applied magnetic field, being larger for layers that exhibit pronounced magnetic hysteresis. A magnetoresistive 1/f noise parameter is proposed, and benchmark values for a variety of spin-valve devices are reported.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.60.Ch Domain walls and domain structure
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities

Room-temperature simultaneously enhanced magnetization and electric polarization in BiFeO3 ceramic synthesized by magnetic annealing

Wanju Luo, Dongliang Wang, Fangwei Wang, Tao Liu, Jianwang Cai, Liyan Zhang, and Yulong Liu

Appl. Phys. Lett. 94, 202507 (2009); http://dx.doi.org/10.1063/1.3139780 (3 pages) | Cited 13 times

Online Publication Date: 20 May 2009

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Multiferroic BiFeO3 ceramics were synthesized by high temperature magnetic annealing using nanosized precursor powders prepared through microwave combustion. Simultaneously enhanced magnetization and electric polarization were observed at room temperature in the sample annealed under an external magnetic field of 10 T. These enhanced properties might be originated from a spin structure severely modulated or the low temperature magnetic phase driven up to room temperature and above by the large external annealing magnetic fields. These results demonstrate that the strong magnetic annealing method is an alternative way to synthesize high performance BiFeO3 materials.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Nt Magnetic annealing and temperature-hysteresis effects
75.80.+q Magnetomechanical effects, magnetostriction
77.80.-e Ferroelectricity and antiferroelectricity
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.22.Ej Polarization and depolarization

Transition width limit in magnetic recording

Xiaobin Wang, Bogdan Valcu, and Nan-Hsiung Yeh

Appl. Phys. Lett. 94, 202508 (2009); http://dx.doi.org/10.1063/1.3141455 (3 pages) | Cited 1 time

Online Publication Date: 20 May 2009

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The minimum magnetization transition width between information bits determines achievable recording linear density. The ultimate limit of this width is determined by the continuous media granular structure. The dependence of the transition width limit on grain size mean and standard deviation are given without an a priori assumption of magnetization transition shape. A simplified approach to combine finite grain size and magnetic field gradient for transition width is discussed.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials

Microwave assisted magnetization reversal in composite media

Shaojing Li, Boris Livshitz, H. Neal Bertram, Manfred Schabes, Thomas Schrefl, Eric E. Fullerton, and Vitaliy Lomakin

Appl. Phys. Lett. 94, 202509 (2009); http://dx.doi.org/10.1063/1.3133354 (3 pages) | Cited 12 times

Online Publication Date: 22 May 2009

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Magnetic reversal in exchange-coupled composite elements under microwave fields is characterized by several unique properties including reduced reversal fields, microwave fields, microwave resonant frequencies, and reduced sensitivity to anisotropy distributions as compared to homogeneous elements. We find that reversal can occur in uniform and nonuniform regimes. The uniform regime is characterized by coherent spin precession enhancement by the microwave field. In the nonuniform regime domain walls in the soft layer mediate reversal and under linearly polarized microwave fields, can lead to a formation of localized reversal/nonreversal areas in the “applied field-frequency” phase plane.
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75.60.Jk Magnetization reversal mechanisms
75.30.Et Exchange and superexchange interactions
75.50.Ss Magnetic recording materials
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Tailoring exchange bias in half-metallic La2/3Sr1/3MnO3 thin films for spin valve applications

P. K. Muduli and R. C. Budhani

Appl. Phys. Lett. 94, 202510 (2009); http://dx.doi.org/10.1063/1.3139770 (3 pages) | Cited 2 times

Online Publication Date: 22 May 2009

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We have utilized the antiferromagnetic nature and structural/chemical compatibility of La0.45Sr0.55MnO3 with highly spin polarized La0.67Sr0.33MnO3 to prepare epitaxial exchange bias (EB) couples. A robust EB shift in magnetization hysteresis with associated interfacial exchange energy J ≈ 0.13 erg/cm2 at 10 K along with enhanced coercivity is reported. The EB effect was engineered to bring coercivity contrast between La0.67Sr0.33MnO3 and cobalt films in La0.45Sr0.55MnO3/La0.67Sr0.33MnO3/SrTiO3/Co magnetic tunnel junctions.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.-b Spin polarized transport
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Electroelastic optical fiber positioning with submicrometer accuracy: Model and experiment

Guggi Kofod, Denis N. Mc Carthy, Jan Krissler, Günter Lang, and Grace Jordan

Appl. Phys. Lett. 94, 202901 (2009); http://dx.doi.org/10.1063/1.3134002 (3 pages) | Cited 9 times

Online Publication Date: 18 May 2009

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We present accurate electromechanical measurements on a balanced push-pull dielectric elastomer actuator, demonstrating submicrometer accurate position control. An analytical model based on a simplified pure-shear dielectric elastomer film with prestretch is found to capture the voltage-displacement behavior, with reduced output due to the boundary conditions. Two complementary experiments show that actuation coefficients of 0.5–1 nm/V2 are obtainable with the demonstrated device, enabling motion control with submicrometer accuracy in a voltage range below 200 V.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
07.07.Tw Servo and control equipment; robots
06.60.Sx Positioning and alignment; manipulating, remote handling
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
42.81.Wg Other fiber-optical devices

Magnetoelectric effect of polymer electrolyte composites with Terfenol-D and lead zirconate titanate inclusions

K. H. Chau, Y. W. Wong, and F. G. Shin

Appl. Phys. Lett. 94, 202902 (2009); http://dx.doi.org/10.1063/1.3138133 (3 pages) | Cited 5 times

Online Publication Date: 19 May 2009

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The magnetoelectric effects of three-phase composites in 0-0-3 connectivity were investigated. The composites consist of particulate Terfenol-D and lead zirconate titanate blended in different polymer matrices. The magnetoelectric coefficient αq, which is the charge density change in response to a change in the applied magnetic field, of the samples was measured under short circuit condition. The results show that the αq of the samples with an electrolytic polymer matrix is larger than that of the samples with an insulating matrix, while samples with an ion-doped electrolytic polymer matrix exhibit the largest αq. These results conform with the expectation that higher matrix conductivity has an effect of enhancing the magnetoelectric signals.
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75.80.+q Magnetomechanical effects, magnetostriction
66.30.H- Self-diffusion and ionic conduction in nonmetals
82.45.Wx Polymers and organic materials in electrochemistry
82.45.Gj Electrolytes

Competing A-site and B-site driven ferroelectric instabilities in the (1−x)PbTiO3-(x)BiAlO3 system

Ajay Kumar Kalyani, Rohini Garg, and Rajeev Ranjan

Appl. Phys. Lett. 94, 202903 (2009); http://dx.doi.org/10.1063/1.3136855 (3 pages) | Cited 7 times

Online Publication Date: 20 May 2009

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The system (1−x)PbTiO3-(x)BiAlO3 has been investigated with regard to its solid solubility, crystal structure, microstructure, and ferroelectric transition. The unit cell volume and the tetragonality exhibit anomalous behavior near x = 0.10. The Curie point (TC) of PbTiO3 was however found to be nearly unchanged. The study seems to suggest that the decrease in the stability of the ferroelectric state due to dilution of the Ti-sublattice by smaller sized Al+3 ions is compensated by the increase in the ferroelectric stability by the Bi+3 ions.
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77.80.B- Phase transitions and Curie point
61.66.Fn Inorganic compounds
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