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28 May 2007

Volume 90, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 221101 (2007); http://dx.doi.org/10.1063/1.2743884 (3 pages)

Siyka I. Shopova, Hongying Zhou, Xudong Fan, and Po Zhang
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Dislocation generation at the coalescence of aluminum nitride lateral epitaxy on shallow-grooved sapphire substrates

J. Mei, F. A. Ponce, R. S. Qhalid Fareed, J. W. Yang, and M. Asif Khan

Appl. Phys. Lett. 90, 221909 (2007); http://dx.doi.org/10.1063/1.2745207 (3 pages) | Cited 6 times

Online Publication Date: 31 May 2007

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The joining of defect-free AlN stripes is observed to trigger the generation of a large density of threading dislocations in the vicinity of the coalescence point. The AlN structure was grown by pulsed lateral epitaxy on shallow-grooved sapphire substrates. In the precoalescence stage, the dislocation density in the lateral epitaxial region (<108 cm−2) is over two orders of magnitude less than in standard c-plane epitaxy. Basal-plane dislocations (b = a = ⅓<11math0>) are generated at the coalescence point as a result of relaxation of compressive stress that develops due to temperature gradients during growth. They bend toward the surface during the postcoalescence growth stage, leading to a high density of pure-edge threading dislocations in the lateral growth regions. Some threading dislocations form loops on prismatic planes in the crystal and the basal segments are observed to glide in the [0001] direction under the electron beam in the microscope.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.37.Lp Transmission electron microscopy (TEM)
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations

Impact-induced glass transition in elastomeric coatings

R. B. Bogoslovov, C. M. Roland, and R. M. Gamache

Appl. Phys. Lett. 90, 221910 (2007); http://dx.doi.org/10.1063/1.2745212 (3 pages) | Cited 20 times

Online Publication Date: 31 May 2007

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Polybutadiene (PB) has a low glass temperature Tg and exhibits rubbery behavior during mechanical perturbation. The corresponding PB-based polyurea (PU) has a higher Tg and fails in a brittle mode for high strain rates. However, unlike in glasses, this brittle failure is accompanied by large energy dissipation. Dielectric relaxation measurements demonstrate that whereas the PB segmental dynamics are faster than the strain rate during impact loading, for PU these motions are on the order of the strain rate, ∼ 105 s−1. Consequently, impact induces a transition to the glassy state, with the accompanying response markedly different from that of a rubber.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
77.22.Gm Dielectric loss and relaxation

Partial-mediated slips in nanocrystalline Ni at high strain rate

X. L. Wu, Y. Qi, and Y. T. Zhu

Appl. Phys. Lett. 90, 221911 (2007); http://dx.doi.org/10.1063/1.2745250 (3 pages) | Cited 14 times

Online Publication Date: 31 May 2007

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Previous experiments on nanocrystalline Ni were conducted under quasistatic strain rates ( ∼ 3×10−3/s), which are much lower than that used in typical molecular dynamics simulations (>3×107/s), thus making direct comparison of modeling and experiments very difficult. In this study, the split Hopkinson bar tests revealed that nanocrystalline Ni prefers twinning to extended partials, especially under higher strain rates (103/s). These observations contradict some reported molecular dynamics simulation results, where only extended partials, but no twins, were observed. The accuracy of the generalized planar fault energies is only partially responsible, but cannot fully account for such a difference.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Mm Grain and twin boundaries
61.46.Hk Nanocrystals

Correction for longitudinal mode vibration in thin slender beams

Cai Liang, Shakib Morshed, and Barton C. Prorok

Appl. Phys. Lett. 90, 221912 (2007); http://dx.doi.org/10.1063/1.2745262 (3 pages) | Cited 18 times

Online Publication Date: 1 June 2007

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This letter reports on a correction to the theoretical prediction of longitudinal mode vibration in thin, slender beams. Thin magnetostrictive strips were fashioned from Metglas™ and subjected to a modulated magnetic field to determine resonant frequency and acoustic wave propagation speed. The results indicated that current analytical solutions were not adequate to predict behavior. Numerical simulations were performed that adjusted Poisson’s ratio until the acoustic wave speed matched that measured in the experiments. The results indicated that the current equations, formulated using the plane-strain modulus, should be modified by using the plane-stress or biaxial modulus.
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46.40.Cd Mechanical wave propagation (including diffraction, scattering, and dispersion)
75.80.+q Magnetomechanical effects, magnetostriction
46.25.Cc Theoretical studies
62.65.+k Acoustical properties of solids

Nanostructure transition: From solid solution Ti(N,C) to nanocomposite nc-Ti(N,C)/a-(C,CNx)

Y. H. Lu and Y. G. Shen

Appl. Phys. Lett. 90, 221913 (2007); http://dx.doi.org/10.1063/1.2745261 (3 pages) | Cited 6 times

Online Publication Date: 1 June 2007

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A nanostructure transition from solid solution (SS) Ti(N,C) to two-phase nanocrystalline (nc)-Ti(N,C)/amorphous (a)-(C,CNx) thin films was investigated using a combination of high-resolution transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. The finding of the authors is that such a nanostructure transition was strongly controlled by the relative atomic ratio x[x ≡ (C+N)/Ti]. The results indicated that SS Ti(N,C) and uncompleted and completed segregated two-phase nanocomposite nc-Ti(N,C)/a-(C,CNx) were successively formed at x ⩽ 1.0, 1.0<x<1.2, and x ≥ 1.2, respectively. Increase of the x values not only decreased the grain size and promoted the formation of more [200]-oriented nanocrystallites but also produced more disorders and defects in thin films. A maximum hardness was achieved for a SS Ti(N,C) structure at x = 1.0. The corresponding nanostructure transition mechanism is also discussed.
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64.70.K- Solid-solid transitions
68.37.Lp Transmission electron microscopy (TEM)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
64.75.-g Phase equilibria
68.55.-a Thin film structure and morphology
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Temperature dependent photoluminescence in oxygen ion implanted and rapid thermally annealed ZnO/ZnMgO multiple quantum wells

Xiaoming Wen, Jeffrey A. Davis, Lap Van Dao, Peter Hannaford, V. A. Coleman, H. H. Tan, C. Jagadish, K. Koike, S. Sasa, M. Inoue, and M. Yano

Appl. Phys. Lett. 90, 221914 (2007); http://dx.doi.org/10.1063/1.2745264 (3 pages) | Cited 10 times

Online Publication Date: 1 June 2007

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The authors investigate the effect of oxygen implantation and rapid thermal annealing in ZnO/ZnMgO multiple quantum wells using photoluminescence. A blueshift in the photoluminescence is observed in the implanted samples. For a low implantation dose, a significant increase of activation energy and a slight increase of the photoluminescence efficiency are observed. This is attributed to the suppression of the point defect complexes and transformation between defect structures by implantation and subsequent rapid thermal annealing. A high dose of implantation leads to lattice damage and agglomeration of defects leading to large defect clusters, which result to an increase in nonradiative recombination.
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78.67.De Quantum wells
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing

Ab Initio atomic simulations of antisite pair recovery in cubic silicon carbide

F. Gao, J. Du, E. J. Bylaska, M. Posselt, and W. J. Weber

Appl. Phys. Lett. 90, 221915 (2007); http://dx.doi.org/10.1063/1.2743751 (3 pages) | Cited 6 times

Online Publication Date: 1 June 2007

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The thermal stability of an antisite pair in cubic silicon carbide (3C-SiC) is studied using ab initio molecular dynamics within the framework of density functional theory. The lifetime of the antisite pair configuration is calculated for temperatures between 1800 and 2250 K, and the effective activation energy for antisite pair recombination is determined to be 2.52 eV. The recombination energy path and static energy barrier are also calculated using the nudged elastic band method along with the dimer method to accurately locate the transition states. The consistency of the results suggests that the antisite pair cannot be correlated with the DI photoluminescence center, as proposed previously by theoretical interpretations. An extended exchange mechanism is found for the antisite pair recombination.
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61.72.J- Point defects and defect clusters
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Hx Other solid inorganic materials
66.30.J- Diffusion of impurities
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Thermodynamic properties and interfacial layer characteristics of HfO2 thin films deposited by plasma-enhanced atomic layer deposition

Inhoe Kim, Seoungwoo Kuk, Seokhoon Kim, Jinwoo Kim, Hyeongtag Jeon, M.-H. Cho, and K.-B. Chung

Appl. Phys. Lett. 90, 222101 (2007); http://dx.doi.org/10.1063/1.2743749 (3 pages) | Cited 4 times

Online Publication Date: 29 May 2007

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The thermodynamic properties and interfacial characteristics of HfO2 thin films that were deposited by the direct plasma atomic layer deposition (DPALD) method are investigated. The as-deposited HfO2 films that were deposited by the DPALD method show crystallization of the HfO2 layers, which initiates at approximately the 35th cycle (about 2.8 nm) of the DPALD process. Medium-energy ion scattering analysis reveals that the direct O2 plasma causes a compositional change in the interfacial layer as the process progresses. With an increase in the number of process cycles, the Si content decreases and the O content increases at that position, so that the HfO2-like Hf-silicate layer is formed on top of the interfacial layer. The enhanced physical reactivity of the oxygen ions in the direct plasma and the Hf-silicate layer may be the driving forces that accelerate the early crystallization of the HfO2 layer in the DPALD process in the as-deposited state.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
65.40.G- Other thermodynamical quantities
68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
52.77.Dq Plasma-based ion implantation and deposition

Three-level structure design and optically controlled current in coupled quantum dots

Weidong Chu, Suqing Duan, and Jia-Lin Zhu

Appl. Phys. Lett. 90, 222102 (2007); http://dx.doi.org/10.1063/1.2743906 (3 pages) | Cited 12 times

Online Publication Date: 29 May 2007

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Two-mode photon-assisted transport through coupled nonidentical quantum dots is studied by designing the level structure of the system. It is found that a Λ-type three-level structure can be formed by modulating the shape and size of dots or by applying electric field. Based on the three-level system, current antiresonance phenomenon occurs due to the effect of coherent population trapping. Using the asymmetry of quantum dots, oscillating current can be produced by rotating the polarization direction of linearly polarized microwave.
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73.63.Kv Quantum dots
78.67.Hc Quantum dots
73.21.La Quantum dots

Excimer laser irradiation induced suppression of off-state leakage current in organic transistors

Wei-Yang Chou, Shih-Ting Lin, Horng-Long Cheng, Fu-Ching Tang, Yow-Jon Lin, Chang-Feng You, and Yu-Wu Wang

Appl. Phys. Lett. 90, 222103 (2007); http://dx.doi.org/10.1063/1.2743925 (3 pages) | Cited 3 times

Online Publication Date: 29 May 2007

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The authors report the suppression of the off-state leakage current and subthreshold swing (SS) in inkjet-printed poly(3-hexylthiophene) thin-film transistors with asymmetric work function source and drain electrodes. Indium tin oxide (ITO) material was used as source/drain electrodes and the source electrode was irradiated by KrF excimer laser. The dominant mechanisms for the suppressive Ioff could be attributed to the increase in the work function of ITO source irradiated by the excimer laser. Lower trap state density formed on the laser irradiated source electrode. Holes could be easily injected into the channel at small lateral electric field resulting in smaller threshold voltage and SS.
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85.30.Tv Field effect devices
85.60.-q Optoelectronic devices

Nickel nanocrystals with HfO2 blocking oxide for nonvolatile memory application

F. M. Yang, T. C. Chang, P. T. Liu, U. S. Chen, P. H. Yeh, Y. C. Yu, J. Y. Lin, S. M. Sze, and J. C. Lou

Appl. Phys. Lett. 90, 222104 (2007); http://dx.doi.org/10.1063/1.2743926 (3 pages) | Cited 32 times

Online Publication Date: 29 May 2007

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A distributed charge storage with Ni nanocrystals embedded in the SiO2 and HfO2 layer has been fabricated in this study. The mean size and aerial density of the Ni nanocrystals are estimated to be about 5 nm and 3.9×1012/cm2, respectively. The nonvolatile memory device with Ni nanocrystals exhibits 1 V threshold voltage shift under 4 V write operation. The device has a long retention time with a small charge lose rate. Besides, the endurance of the memory device is not degraded up to 106 write/erase cycles.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.30.Sk Pulse and digital circuits

H2S exposure of a (100)Ge surface: Evidences for a (2×1) electrically passivated surface

M. Houssa, D. Nelis, D. Hellin, G. Pourtois, T. Conard, K. Paredis, K. Vanormelingen, A. Vantomme, M. K. Van Bael, J. Mullens, M. Caymax, M. Meuris, and M. M. Heyns

Appl. Phys. Lett. 90, 222105 (2007); http://dx.doi.org/10.1063/1.2743385 (3 pages) | Cited 10 times

Online Publication Date: 30 May 2007

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The experimental study of the bonding geometry of a (100)Ge surface exposed to H2S in the gas phase at 330 °C shows that 1 ML S coverage with (2×1) surface reconstruction can be achieved. The amount of S on the Ge surface and the observed surface periodicity can be explained by the formation of disulfide bridges between Ge–Ge dimers on the surface. First-principles molecular dynamics simulations confirm the preserved (2×1) reconstruction after dissociative adsorption of H2S molecules on a (100)Ge (2×1) surface, and predict the formation of (S–H)–(S–H) inter-Ge dimer bridges, i.e., disulfide bridges interacting via hydrogen bonding. The computed energy band gap of this atomic configuration is shown to be free of surface states, a very important finding for the potential application of Ge in future high performance integrated circuits.
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81.65.Rv Passivation
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.43.Bc Ab initio calculations of adsorbate structure and reactions
71.20.Mq Elemental semiconductors

Interaction of dislocations with vacancies in silicon: Electronic effects

M. M. de Araýýjo, J. F. Justo, and R. W. Nunes

Appl. Phys. Lett. 90, 222106 (2007); http://dx.doi.org/10.1063/1.2743909 (3 pages) | Cited 1 time

Online Publication Date: 30 May 2007

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The authors report on an ab initio investigation of the interaction of vacancies with the core of 90° partial dislocation in silicon. For the single-period and the double-period core reconstructions, they find the vacancy formation energies at the core sites to be lower than in the crystalline environment. Moreover, they find that the vacancy-dislocation coupling does not change the U-negative nature of a vacancy in silicon, but leads to quantitative changes in the relative stability of different charge states, as the Fermi level sweeps the electronic band gap in this material.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Bb Theories and models of crystal defects
71.20.Mq Elemental semiconductors
71.15.-m Methods of electronic structure calculations

Transparent metallic Sb-doped SnO2 nanowires

Qing Wan, Eric N. Dattoli, and Wei Lu

Appl. Phys. Lett. 90, 222107 (2007); http://dx.doi.org/10.1063/1.2743746 (3 pages) | Cited 40 times

Online Publication Date: 30 May 2007

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The authors report the growth and characterization of single-crystalline, degenerately Sb-doped SnO2 (SnO2:Sb) nanowires. The in situ doped SnO2:Sb nanowires are transparent conductors with resistivities down to 4.1×10−4 Ω cm and failure-current densities up to 2.1×107 A/cm2. High carrier concentrations (>1020 cm−3) and minimal environmental effects were also observed and attributed to effective Sb doping. The SnO2:Sb nanowires can be obtained at large quantities using a low-cost vapor transport method and may provide a suitable alternative to indium tin oxide as transparent conducting oxide materials. Field emission devices with SnO2:Sb nanowire cathodes and anodes exhibited an ultralow turn-on voltage of 2 V.
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68.65.La Quantum wires (patterned in quantum wells)
81.07.Bc Nanocrystalline materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.up Other materials
73.63.Bd Nanocrystalline materials

Concentration-dependent mobility in organic field-effect transistors probed by infrared spectromicroscopy of the charge density profile

A. D. Meyertholen, Z. Q. Li, D. N. Basov, M. M. Fogler, M. C. Martin, G. M. Wang, A. S. Dhoot, D. Moses, and A. J. Heeger

Appl. Phys. Lett. 90, 222108 (2007); http://dx.doi.org/10.1063/1.2745223 (3 pages) | Cited 4 times

Online Publication Date: 31 May 2007

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The authors show that infrared imaging of the charge density profile in organic field-effect transistors (FETs) can probe transport characteristics which are difficult to access by conventional contact-based measurements. Specifically, they carry out experiments and modeling of infrared spectromicroscopy of poly(3-hexylthiophene) (P3HT) FETs in which charge injection is affected by a relatively low resistance of the gate insulators. They conclude that the mobility of P3HT has a power-law density dependence, which is consistent with the activated transport in disorder-induced tails of the density of states.
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85.30.Tv Field effect devices

Memory effect of CdSe/ZnS nanoparticles embedded in a conducting poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] polymer layer

Fushan Li, Dong-Ick Son, Han-Moe Cha, Seung-Mi Seo, Bong-Jun Kim, Hyuk-Ju Kim, Jae-Hun Jung, and Tae Whan Kim

Appl. Phys. Lett. 90, 222109 (2007); http://dx.doi.org/10.1063/1.2745219 (3 pages) | Cited 22 times

Online Publication Date: 31 May 2007

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Capacitance-voltage (C-V) measurements on Au/a conducting poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] polymer layer containing core/shell CdSe/ZnS nanoparticles (hybrid layer)/indium tin oxide (ITO) coated glass and Al/hybrid layer/ITO coated glass capacitors at 300 K showed metal-insulator-semiconductor behavior with a large flatband voltage shift. This shift was due to the existence of the CdSe/ZnS nanoparticles, indicative of trapping, storing, and emission of charge carriers in the CdSe/ZnS nanoparticles. Symmetric and asymmetric C-V characteristics appeared in the Al/hybrid layer/ITO coated glass and Au/hybrid layer/ITO coated glass capacitors, respectively. A dipolar carrier trapping model is proposed to explain the symmetric behavior in the C-V curve.
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84.30.Sk Pulse and digital circuits
84.32.Tt Capacitors

Room-temperature ferromagnetic and ferroelectric behavior in polycrystalline ZnO-based thin films

Yuan-Hua Lin, Minghao Ying, Ming Li, Xiaohui Wang, and Ce-Wen Nan

Appl. Phys. Lett. 90, 222110 (2007); http://dx.doi.org/10.1063/1.2745247 (3 pages) | Cited 23 times

Online Publication Date: 31 May 2007

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Polycrystalline ZnO-based thin films with Li and/or Co doping have been prepared by a sol-gel spin-coating method on silicon substrates. Magnetization measurements reveal that Li-doped ZnO film shows paramagnetic behavior. However, the Co-doped ZnO thin films show obvious room-temperature ferromagnetic properties, and ferromagnetic properties can be enhanced by the Li codoping, which may be ascribed to indirect exchange via Li-related defects. All ZnO-based films exhibit ferroelectric behavior, and ferroelectric properties can be tuned by the dopants.
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77.80.-e Ferroelectricity and antiferroelectricity
61.72.up Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals

Band discontinuity measurements of the wafer bonded InGaAs/Si heterojunction

Kyle S. McKay, Felix P. Lu, Jungsang Kim, Changhyun Yi, April S. Brown, and Aaron R. Hawkins

Appl. Phys. Lett. 90, 222111 (2007); http://dx.doi.org/10.1063/1.2745254 (3 pages) | Cited 2 times

Online Publication Date: 31 May 2007

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p-type InGaAs/Si heterojunctions were fabricated through a wafer fusion bonding process. The relative band alignment between the two materials at the heterointerface was determined using current-voltage (I-V) measurements and applying thermionic emission-diffusion theory. The valence and conduction band discontinuities for the InGaAs/Si interface were determined to be 0.48 and −0.1 eV, respectively, indicating a type-II band alignment.
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73.20.At Surface states, band structure, electron density of states
79.40.+z Thermionic emission
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

PbTe nanocomposites synthesized from PbTe nanocrystals

J. Martin, G. S. Nolas, W. Zhang, and L. Chen

Appl. Phys. Lett. 90, 222112 (2007); http://dx.doi.org/10.1063/1.2745218 (3 pages) | Cited 52 times

Online Publication Date: 1 June 2007

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Dense lead telluride (PbTe) nanocomposites were prepared from PbTe nanocrystals synthesized employing an aqueous solution-phase reaction. This approach reproducibly synthesizes 100–150 nm nanocrystals with a high yield of over 2 g per batch. Densification using spark plasma sintering dimensionally integrated nanoscale grains within a bulk matrix, resulting in a uniform dispersion of nonconglomerated nanocrystals. Transport properties of PbTe nanocomposites were evaluated through temperature dependent resistivity, Hall, Seebeck coefficient, and thermal conductivity measurements. These nanocomposites show an enhancement in the thermoelectric properties compared to bulk polycrystalline PbTe with similar carrier concentrations. Our results also indicate a strong sensitivity to stoichiometry, surface oxygen adsorption, and porosity.
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81.16.Be Chemical synthesis methods
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.43.Mn Adsorption kinetics
52.77.-j Plasma applications
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Enhancement of photoinduced effects in Bi1−xCaxMnO3 thin films

V. N. Smolyaninova, E. Talanova, Rajeswari M. Kolagani, G. Yong, R. Kennedy, M. Steger, D. Schaefer, and K. Wall

Appl. Phys. Lett. 90, 222501 (2007); http://dx.doi.org/10.1063/1.2743948 (3 pages)

Online Publication Date: 30 May 2007

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A considerable increase of the photoinduced resistivity changes and the lifetime of these changes were found in the Bi0.4Ca0.6MnO3 thin films after depositing gold nanoparticles on the surface. A possible interpretation of this effect may be the enhancement of local electromagnetic field at the interface between the film and the metal nanoparticles due to the plasmon resonance, which may promote formation of larger volume of conducting phase producing larger magnitude and the lifetime of photoinduced resistivity changes.
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73.61.Ng Insulators
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Colossal electroresistance without colossal magnetoresistance in La0.9Sr0.1MnO3

N. Biškup, A. de Andrés, N. M. Nemes, M. García-Hernandez, K. V. Glazyrin, and Y. M. Mukovskii

Appl. Phys. Lett. 90, 222502 (2007); http://dx.doi.org/10.1063/1.2745220 (3 pages) | Cited 7 times

Online Publication Date: 31 May 2007

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The authors report on colossal electroresistance (ER) in the ferromagnetic insulator manganite La0.9Sr0.1MnO3. The single crystal samples exhibit a transition into a low resistive state above a certain threshold current. Pulsed measurements demonstrate that this transition is not a consequence of heating. ER behaves similarly to magnetoresistance (MR) above the orbital order temperature TOO. Below TOO the MR is only 20% while ER enhances the conductivity by several orders of magnitude. Magnetic field and electric current have opposite effects on the conductivity, therefore, it seems that only the injected carriers are able to modify the ordering of eg Mn orbitals.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Sk Insulators
75.50.Dd Nonmetallic ferromagnetic materials

Signatures of enhanced ordering temperatures in digital superlattices of (LaMnO3)m/(SrMnO3)2m

A. Bhattacharya, X. Zhai, M. Warusawithana, J. N. Eckstein, and S. D. Bader

Appl. Phys. Lett. 90, 222503 (2007); http://dx.doi.org/10.1063/1.2745205 (3 pages) | Cited 26 times

Online Publication Date: 31 May 2007

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Digital superlattices of (LaMnO3)m/SrMnO3)2m (m ⩽ 3) having the same nominal composition as La1/3Sr2/3MnO3, an antiferromagnetic insulator, have been synthesized by means of molecular beam epitaxy. All superlattices show a sharp resistive maximum at temperatures near to or higher than the Néel temperature of bulk La1/3Sr2/3MnO3. No discernible signatures of magnetic ordering are observed near the resistivity peak for m ⩽ 2, but m = 3 has a susceptibility peak consistent with antiferromagnet ordering, which is canted when cooled in a small magnetic field. Analogies are drawn to dx2−y2 orbitally ordered, layered antiferromagnetic manganites to explain the observations.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
73.63.-b Electronic transport in nanoscale materials and structures

Temperature- and magnetic-field-induced phase transitions in Fe-rich FePt alloys

Chuan-Bing Rong and J. Ping Liu

Appl. Phys. Lett. 90, 222504 (2007); http://dx.doi.org/10.1063/1.2745255 (3 pages) | Cited 10 times

Online Publication Date: 1 June 2007

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Structural and magnetic properties of the FexPt100−x (x = 78–88) alloys have been investigated. It is found that for all of the investigated compositions, a phase transition occurs from the disordered γ phase to the ordered α phase during cooling, while a reverse process takes place during heating. Moreover, magnetic fields also induce a phase transition from the γ phase to the α phase near the transition temperature. The temperature- and magnetic-field-induced phase transitions give rise to a huge negative thermal expansion and thus a giant magnetic entropy change (up to 39.8 J/kg K for the alloy with x = 79). The contribution of the magnetic field induced phase transition to the total magnetic entropy change is estimated to be around 20%–25%.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
81.40.Gh Other heat and thermomechanical treatments
75.50.Bb Fe and its alloys

Effects of hydrogenated annealing on structural defects, conductivity, and magnetic properties of V-doped ZnO powders

S. H. Liu, H. S. Hsu, C. R. Lin, C. S. Lue, and J. C. A. Huang

Appl. Phys. Lett. 90, 222505 (2007); http://dx.doi.org/10.1063/1.2745642 (3 pages) | Cited 20 times

Online Publication Date: 1 June 2007

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The structure, electrical property, and magnetism of 7.5% V-doped ZnO powders that were hydrogenated annealed at 300, 500, and 700 °C have been systematically investigated. The saturation magnetization and conductivity of the V:ZnO powders increase with hydrogenated annealing temperature (Tha), and the magnetization-temperature curves transform from paramagnetism to weak ferromagnetism ( ∼ 10−4μB/V atom) as Tha increases. The results suggest that ferromagnetism in V:ZnO powders is highly correlated to the structural defects.
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75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.80.Ey III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing

Theory for symmetric toggle magnetic random access memory

D. C. Worledge, P. L. Trouilloud, and W. J. Gallagher

Appl. Phys. Lett. 90, 222506 (2007); http://dx.doi.org/10.1063/1.2743899 (3 pages) | Cited 10 times

Online Publication Date: 1 June 2007

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The authors analyze the critical switching curve for two identical coupled magnetic free layers, as used in toggle magnetic random access memory. The continuous and discontinuous transitions between different magnetic states are described. A general criteria for toggling is derived by summing up the number of clockwise and counterclockwise transitions, leading to a larger toggle region than previously reported. It also leads to a significant chirality effect, wherein the toggle region shifts depending on the order in which the word and bit line fields are applied. Finally, the authors discuss a type of switching useful for experimentally measuring the critical switching curve.
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85.75.Dd Magnetic memory using magnetic tunnel junctions
85.70.Ay Magnetic device characterization, design, and modeling
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
84.30.Sk Pulse and digital circuits
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