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22 Oct 2012

Volume 101, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 171101 (2012); http://dx.doi.org/10.1063/1.4758996 (4 pages)

Wolfram H. P. Pernice and Harish Bhaskaran
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Tunable phononic crystals based on cylindrical Hertzian contact

Feng Li, Duc Ngo, Jinkyu Yang, and Chiara Daraio

Appl. Phys. Lett. 101, 171903 (2012); http://dx.doi.org/10.1063/1.4762832 (4 pages)

Online Publication Date: 23 October 2012

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We investigate the tunability of phononic crystals consisting of arrays of cylindrical elements using theoretical, numerical, and experimental approaches. We show that when these systems are excited by a continuous dynamic signal under large static precompression, they support a characteristic band structure whose cutoff frequency can be controlled by changing the alignment angles or the static precompression. Furthermore, we report the formation of an additional pass band when there exists particles' eccentricity, which is caused by the coupling mechanism between longitudinal and shear modes.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.20.-b Electron density of states and band structure of crystalline solids

Modulated structure in the martensite phase of Ni1.8Pt0.2MnGa: A neutron diffraction study

Sanjay Singh, K. R. A. Ziebeck, E. Suard, P. Rajput, S. Bhardwaj, A. M. Awasthi, and S. R. Barman

Appl. Phys. Lett. 101, 171904 (2012); http://dx.doi.org/10.1063/1.4760270 (4 pages) | Cited 1 time

Online Publication Date: 23 October 2012

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7M orthorhombic modulated structure in the martensite phase of Ni1.8Pt0.2MnGa is reported by powder neutron diffraction study, which indicates that it is likely to exhibit magnetic field induced strain. The change in the unit cell volume is less than 0.5% between the austenite and the martensite phases, as expected for a volume conserving martensite transformation. The magnetic structure analysis shows that the magnetic moment in the martensite phase is higher compared to Ni2MnGa, which is in good agreement with magnetization measurement.
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81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Cc Other ferromagnetic metals and alloys

Fe-doped InN layers grown by molecular beam epitaxy

Xinqiang Wang, Shitao Liu, Dingyu Ma, Xiantong Zheng, Guang Chen, Fujun Xu, Ning Tang, Bo Shen, Peng Zhang, Xingzhong Cao, Baoyi Wang, Sen Huang, Kevin J. Chen, Shengqiang Zhou, and Akihiko Yoshikawa

Appl. Phys. Lett. 101, 171905 (2012); http://dx.doi.org/10.1063/1.4764013 (4 pages)

Online Publication Date: 24 October 2012

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Iron(Fe)-doped InN (InN:Fe) layers have been grown by molecular beam epitaxy. It is found that Fe-doping leads to drastic increase of residual electron concentration, which is different from the semi-insulating property of Fe-doped GaN. However, this heavy n-type doping cannot be fully explained by doped Fe-concentration ([Fe]). Further analysis shows that more unintentionally doped impurities such as hydrogen and oxygen are incorporated with increasing [Fe] and the surface is degraded with high density pits, which probably are the main reasons for electron generation and mobility reduction. Photoluminescence of InN is gradually quenched by Fe-doping. This work shows that Fe-doping is one of good choices to control electron density in InN.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.up Other materials
72.20.Fr Low-field transport and mobility; piezoresistance
78.55.Hx Other solid inorganic materials

Harnessing electromechanical membrane wrinkling for actuation

Andrew T. Conn and Jonathan Rossiter

Appl. Phys. Lett. 101, 171906 (2012); http://dx.doi.org/10.1063/1.4764101 (4 pages) | Cited 2 times

Online Publication Date: 24 October 2012

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Dielectric elastomers are soft electromechanical transducers that can exhibit unstable wrinkling behavior under large electric fields. This instability can be exploited by optimizing electrode boundaries to accentuate or attenuate localized wrinkling. An analytical model is presented, which demonstrates that the critical electric field to induce wrinkling can be lowered as the electrode geometry changes from convex to concave. This allows a single dielectric elastomer membrane to generate either biaxial or uniaxial extension in specific regions. A prototype 56 μm thick membrane actuator incorporates this principle to generate an in-plane rotational output, producing an actuation stroke of 15.7°.
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07.07.Mp Transducers
FREE

Patterned optical anisotropy in woven conjugated polymer systems

C. Müller, M. Garriga, and M. Campoy-Quiles

Appl. Phys. Lett. 101, 171907 (2012); http://dx.doi.org/10.1063/1.4764518 (5 pages)

Online Publication Date: 25 October 2012

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Weaving of highly oriented conjugated polymer/polyethylene tapes is demonstrated to permit the generation of concealed patterns that can be detected under appropriate polarized light illumination. This is achieved by exploiting the fact that the amount of transmitted light varies with the superposition sequence of semi-transparent objects that feature a high degree of linear birefringence as well as linear dichroism. An analysis based on Müller calculus provides a theoretical description of the observed optical behavior.
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78.66.Qn Polymers; organic compounds
42.70.Jk Polymers and organics
78.20.Fm Birefringence

Bulk silica-based luminescent materials by sol-gel processing of non-conventional precursors

J. A. Rodríguez, C. Fernández-Sánchez, C. Domínguez, S. Hernández, and Y. Berencén

Appl. Phys. Lett. 101, 171908 (2012); http://dx.doi.org/10.1063/1.4764561 (4 pages)

Online Publication Date: 25 October 2012

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The sol-gel synthesis of bulk silica-based luminescent materials using innocuous hexaethoxydisilane and hexamethoxydisilane monomers, followed by one hour thermal annealing in an inert atmosphere at 950 °C–1150 °C, is reported. As-synthesized hexamethoxydisilane-derived samples exhibit an intense blue photoluminescence band, whereas thermally treated ones emit stronger photoluminescence radiation peaking below 600 nm. For hexaethoxydisilane-based material, annealed at or above 1000 °C, a less intense photoluminescence band, peaking between 780 nm and 850 nm that is attributed to nanocrystalline silicon is observed. Mixtures of both precursors lead to composed spectra, thus envisaging the possibility of obtaining pre-designed spectral behaviors by varying the mixture composition.
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78.55.Hx Other solid inorganic materials
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)
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing
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Stress evaluation in thin strained-Si film by polarized Raman spectroscopy using localized surface plasmon resonance

Hiroki Hashiguchi, Munehisa Takei, Daisuke Kosemura, and Atsushi Ogura

Appl. Phys. Lett. 101, 172101 (2012); http://dx.doi.org/10.1063/1.4761959 (3 pages)

Online Publication Date: 22 October 2012

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We evaluated the stress in a thin strained-Si film on relaxed SiGe on a surface-oxidized Si substrate using surface enhanced Raman scattering (SERS). The strained-Si peak was enhanced by the SERS technique. However, the strained-Si peak shifted toward a higher wavenumber while the peaks from the Si substrate were unchanged. We performed Raman measurement under the optical geometry in LO and TO phonon active conditions. From these measurements, it was clarified that the peak shift was attributed to the TO phonon peak that appeared, which was caused by the excitation of the z polar component in the near-field light.
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78.66.Db Elemental semiconductors and insulators
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Hv Other nonmetallic inorganics

Growth of wurtzite InN on bulk In2O3(111) wafers

Sergey Sadofev, YongJin Cho, Oliver Brandt, Manfred Ramsteiner, Raffaella Calarco, Henning Riechert, Steven C. Erwin, Zbigniew Galazka, Maxym Korytov, Martin Albrecht, Reinhard Uecker, and Roberto Fornari

Appl. Phys. Lett. 101, 172102 (2012); http://dx.doi.org/10.1063/1.4761985 (4 pages) | Cited 1 time

Online Publication Date: 22 October 2012

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A single phase InN epitaxial film is grown on a bulk In2O3(111) wafer by plasma-assisted molecular beam epitaxy. The InN/In2O3 orientation relationship is found to be (0001) ‖ (111) and [1math00] ‖ [11math]. High quality of the layer is confirmed by the small widths of the x-ray rocking curves, the sharp interfaces revealed by transmission electron microscopy, the narrow spectral width of the Raman E2h vibrational mode, and the position of the photoluminescence band close to the fundamental band gap of InN.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
63.22.Dc Free films

Fermi-level depinning at the metal-germanium interface by the formation of epitaxial nickel digermanide NiGe2 using pulsed laser anneal

Phyllis Shi Ya Lim, Dong Zhi Chi, Xin Cai Wang, and Yee-Chia Yeo

Appl. Phys. Lett. 101, 172103 (2012); http://dx.doi.org/10.1063/1.4762003 (4 pages) | Cited 1 time

Online Publication Date: 22 October 2012

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A reduced effective electron Schottky barrier height ΦBn,eff of 0.37 eV is obtained at the epitaxial-NiGe2/Ge(100) interface. This is substantially lower than an ΦBn,eff of 0.60 eV obtained at the NiGe/Ge(100) interface. The Fermi-level pinning effect, which is commonly observed between metals and Ge, is reduced at the NiGe2/Ge(100) interface. This is attributed to the formation of epitaxial NiGe2 on Ge(100), which is expected to have a lower density of interface states due to reduced number of dangling bonds.
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73.40.Ns Metal-nonmetal contacts
73.20.At Surface states, band structure, electron density of states
68.55.at Other materials
61.72.Cc Kinetics of defect formation and annealing
73.30.+y Surface double layers, Schottky barriers, and work functions

Effective passivation of In0.2Ga0.8As by HfO2 surpassing Al2O3 via in-situ atomic layer deposition

Y. H. Chang, C. A. Lin, Y. T. Liu, T. H. Chiang, H. Y. Lin, M. L. Huang, T. D. Lin, T. W. Pi, J. Kwo, and M. Hong

Appl. Phys. Lett. 101, 172104 (2012); http://dx.doi.org/10.1063/1.4762833 (5 pages) | Cited 3 times

Online Publication Date: 22 October 2012

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High κ gate dielectrics of HfO2 and Al2O3 were deposited on molecular beam epitaxy-grown In0.2Ga0.8As pristine surface using in-situ atomic-layer-deposition (ALD) without any surface treatment or passivation layer. The ALD-HfO2/p-In0.2Ga0.8As interface showed notable reduction in the interfacial density of states (Dit), deduced from quasi-static capacitance-voltage and conductance-voltage (G-V) at room temperature and 100 °C. More significantly, the midgap peak commonly observed in the Dit(E) of ALD-oxides/In0.2Ga0.8As is now greatly diminished. The midgap Dit value decreases from ≥15 × 1012 eV−1 cm−2 for ALD-Al2O3 to ∼2–4 × 1012 eV−1 cm−2 for ALD-HfO2. Further, thermal stability at 850 °C was achieved in the HfO2/In0.2Ga0.8As, whereas C-V characteristics of Al2O3/p-In0.2Ga0.8As degraded after the high temperature annealing. From in-situ x-ray photoelectron spectra, the AsOx, which is not the oxidized state from the native oxide, but is an induced state from adsorption of trimethylaluminum and H2O, was found at the ALD-Al2O3/In0.2Ga0.8As interface, while that was not detected at the ALD-HfO2/In0.2Ga0.8As interface.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Rv Passivation
77.55.dj For nonsilicon electronics (Ge, III-V, II-VI, organic electronics)
68.43.Mn Adsorption kinetics

Single photon emission from impurity centers in AlGaAs epilayers on Ge and Si substrates

S. Minari, L. Cavigli, F. Sarti, M. Abbarchi, N. Accanto, G. Muñoz Matutano, S. Bietti, S. Sanguinetti, A. Vinattieri, and M. Gurioli

Appl. Phys. Lett. 101, 172105 (2012); http://dx.doi.org/10.1063/1.4761939 (4 pages) | Cited 1 time

Online Publication Date: 23 October 2012

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We show that the epitaxial growth of thin layers of AlGaAs on Ge and Si substrates allows to obtain single photon sources by exploiting the sparse and unintentional contamination with acceptors of the AlGaAs. Very bright and sharp single photoluminescence lines are observed in confocal microscopy. These lines behave very much as single excitons in quantum dots, but their implementation is by far much easier, since it does not require 3D nucleation. The photon antibunching is demonstrated by time resolved Hanbury Brown and Twiss measurements.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena
68.55.ag Semiconductors
78.47.jd Time resolved luminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Temperature dependent band offsets in PbSe/PbEuSe quantum well heterostructures

M. Simma, G. Bauer, and G. Springholz

Appl. Phys. Lett. 101, 172106 (2012); http://dx.doi.org/10.1063/1.4759145 (5 pages)

Online Publication Date: 23 October 2012

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The band offsets of PbSe/Pb1−xEuxSe multi-quantum wells grown by molecular beam epitaxy are determined as a function of temperature and europium content using temperature-modulated differential transmission spectroscopy. The confined quantum well states in the valence and conduction bands are analyzed using a k·p model with envelope function approximation. From the fit of the experimental data, the normalized conduction band offset is determined as 0.45±0.15 of the band gap difference, independently of Eu content up to 14% and temperature from 20 to 300 K.
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73.21.Fg Quantum wells
81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.20.-b Electron density of states and band structure of crystalline solids
73.21.La Quantum dots

Depressed scattering across grain boundaries in single crystal graphene

Jiao Chen, Zhi Jin, Peng Ma, Hong Wang, Haomin Wang, Jingyuan Shi, Songang Peng, Xinyu Liu, and Tianchun Ye

Appl. Phys. Lett. 101, 172107 (2012); http://dx.doi.org/10.1063/1.4758464 (4 pages)

Online Publication Date: 23 October 2012

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We investigated the electrical and quantum properties of single-crystal graphene (SCG) synthesized by chemical vapor deposition (CVD). Quantum Hall effect and Shubnikov de Hass oscillation, a distinguishing feature of a 2-dimensional electronic material system, were observed during the low temperature transport measurements. Decreased scattering from grain boundaries in SCG was proven through extracting information from weak localization theory. Our results facilitate understanding the electrical properties of SCG grown by CVD and its applications in high speed transistor and quantum devices.
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61.72.Mm Grain and twin boundaries
73.20.Fz Weak or Anderson localization
73.43.-f Quantum Hall effects
61.48.Gh Structure of graphene
72.80.Vp Electronic transport in graphene
81.05.ue Graphene

Ultra-high hole mobility exceeding one million in a strained germanium quantum well

A. Dobbie, M. Myronov, R. J. H. Morris, A. H. A. Hassan, M. J. Prest, V. A. Shah, E. H. C. Parker, T. E. Whall, and D. R. Leadley

Appl. Phys. Lett. 101, 172108 (2012); http://dx.doi.org/10.1063/1.4763476 (4 pages)

Online Publication Date: 23 October 2012

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In this paper, we report a Hall mobility of one million in a germanium two-dimensional hole gas. The extremely high hole mobility of 1.1 × 106 cm2 V−1 s−1 at a carrier sheet density of 3 × 1011 cm−2 was observed at 12 K. This mobility is nearly an order of magnitude higher than any previously reported. From the structural analysis of the material and mobility modeling based on the relaxation time approximation, we attribute this result to the combination of a high purity Ge channel and a very low background impurity level that is achieved from the reduced-pressure chemical vapor deposition growth method.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
73.63.Hs Quantum wells
71.55.Cn Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Critical flux ratio of hydrogen radical to film precursor in microcrystalline silicon deposition for solar cells

Yusuke Abe, Atsushi Fukushima, Keigo Takeda, Hiroki Kondo, Kenji Ishikawa, Makoto Sekine, and Masaru Hori

Appl. Phys. Lett. 101, 172109 (2012); http://dx.doi.org/10.1063/1.4764065 (3 pages) | Cited 1 time

Online Publication Date: 23 October 2012

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The properties of thin-film silicon grown by plasma enhanced chemical vapor deposition were investigated with respect to the flux ratio of hydrogen radical to film precursor. The absolute density and translational temperature of H radicals in SiH4/H2 capacitively coupled plasma were measured using vacuum ultraviolet laser absorption spectroscopy. The flux of effective H radicals to the surface reactions was estimated from the results. The flux of effective film precursor for deposition was estimated from the deposition rate, so that the critical flux ratio of H radicals to film precursor to obtain suitable film properties was identified to be approximately 65–70.
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88.40.jj Silicon solar cells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.40.Fy Semiconductors

Anomalous transport of Sb in laser irradiated Ge

E. Bruno, G. G. Scapellato, A. La Magna, M. Cuscunà, E. Napolitani, S. Boninelli, F. Priolo, G. Fortunato, and V. Privitera

Appl. Phys. Lett. 101, 172110 (2012); http://dx.doi.org/10.1063/1.4764069 (5 pages) | Cited 1 time

Online Publication Date: 24 October 2012

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Excimer laser annealing is shown to be very promising to promote Sb incorporation in Ge up to concentrations as high as 1 × 1021 at./cm3. However, we demonstrate that when Ge is melted by laser irradiation, a high excess of vacancies is generated in the molten region. These vacancies induce Sb electrical deactivation at the melt depth through the formation of Sbm-Vn complexes that act as a sink for further Sb atoms, even leading Sb to back-diffuse towards the surface, against the concentration gradient. These results are fundamental for the realization of new generation Ge-based micro and optoelectronic devices.
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79.20.Ds Laser-beam impact phenomena
61.82.Fk Semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.jd Vacancies
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation

Direct observation of grain growth from molten silicon formed by micro-thermal-plasma-jet irradiation

Shohei Hayashi, Yuji Fujita, Takahiro Kamikura, Kohei Sakaike, Muneki Akazawa, Mitsuhisa Ikeda, Hiroaki Hanafusa, and Seiichiro Higashi

Appl. Phys. Lett. 101, 172111 (2012); http://dx.doi.org/10.1063/1.4764522 (4 pages)

Online Publication Date: 26 October 2012

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Phase transformation of amorphous-silicon during millisecond annealing using micro-thermal-plasma-jet irradiation was directly observed using a high-speed camera with microsecond time resolution. An oval-shaped molten-silicon region adjacent to the solid phase crystallization region was clearly observed, followed by lateral large grain growth perpendicular to a liquid-solid interface. Furthermore, leading wave crystallization (LWC), which showed intermittent explosive crystallization, was discovered in front of the moving molten region. The growth mechanism of LWC has been investigated on the basis of numerical simulation implementing explosive movement of a thin liquid layer driven by released latent heat diffusion in a lateral direction.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
61.72.Cc Kinetics of defect formation and annealing
61.80.-x Physical radiation effects, radiation damage
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
66.30.-h Diffusion in solids
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Magnetocaloric properties of La0.7Ca0.3Mn16O3 and La0.7Ca0.3Mn18O3 manganites and their “sandwich”

A. M. Aliev, A. G. Gamzatov, K. I. Kamilov, A. R. Kaul, and N. A. Babushkina

Appl. Phys. Lett. 101, 172401 (2012); http://dx.doi.org/10.1063/1.4761953 (4 pages) | Cited 3 times

Online Publication Date: 22 October 2012

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The effect of 16О → 18О isotope substitution on specific heat and magnetocaloric effect of polycrystalline La0.7Ca0.3MnO3 manganite is studied. Mainly the effect of isotope substitution for the specific heat and magnetocaloric effect is only the reduction of temperatures of anomalies. ΔTad values at magnetic field change ΔH = 18 kOe are equal to ΔTad = 2.41 K and 2.60 K for La0.7Ca0.3Mn16O3 (LCMO16) and La0.7Ca0.3Mn18O3 (LCMO18), respectively. The sandwich of the LCMO16 and LCMO18 samples was produced for direct measurement of ΔTad. The use of sandwich from materials with near similar magnetocaloric properties increases the relative cooling power by about 20%.
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75.30.Sg Magnetocaloric effect, magnetic cooling
65.40.Ba Heat capacity
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Effective magnetic anisotropy of annealed FePt nanoparticles

N. A. Usov and J. M. Barandiarán

Appl. Phys. Lett. 101, 172402 (2012); http://dx.doi.org/10.1063/1.4761978 (4 pages)

Online Publication Date: 22 October 2012

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The hysteresis loops of randomly oriented assembly of FePt nanoparticles are calculated numerically as a function of particle diameter for the range of the effective anisotropy constants, Kef = 1-5 × 107 erg/cm3, taking into account the effect of thermal fluctuations. Very sharp dependence of the assembly coercive force on the particle diameter is found for Kef  ≥ 3 × 107 erg/cm3. The effective anisotropy constant of annealed FePt nanoparticle is estimated assuming the existence of L10 inclusions distributed randomly in a magnetically soft surrounding matrix. The hysteresis loop evolution can be explained if the total volume of the L10 grains is supposed to increase during annealing.
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75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments
75.40.Mg Numerical simulation studies
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Voltage-gated modulation of domain wall creep dynamics in an ultrathin metallic ferromagnet

Uwe Bauer, Satoru Emori, and Geoffrey S. D. Beach

Appl. Phys. Lett. 101, 172403 (2012); http://dx.doi.org/10.1063/1.4764071 (4 pages)

Online Publication Date: 24 October 2012

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The influence of gate voltage, temperature, and magnetic field on domain wall (DW) creep dynamics is investigated in Pt/Co/gadolinium oxide (GdOx) films with perpendicular magnetic anisotropy and imaged by a scanning magneto-optical Kerr effect technique. The DW creep velocity can be controlled by an electric field applied to the Co/GdOx interface via a linear modulation of the activation energy barrier with gate voltage. At low speeds, the DW velocity can be changed significantly by a gate voltage, but the effect is diminished as the DW velocity increases, which limits electric field control of fast DW motion.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
78.20.Ls Magneto-optical effects

The magnetic structure of an epitaxial BiMn0.5Fe0.5O3 thin film on SrTiO3 (001) studied with neutron diffraction

D. L. Cortie, A. P. J. Stampfl, F. Klose, Y. Du, X. L. Wang, H. Y. Zhao, H. Kimura, and Z. X. Cheng

Appl. Phys. Lett. 101, 172404 (2012); http://dx.doi.org/10.1063/1.4762818 (4 pages) | Cited 1 time

Online Publication Date: 25 October 2012

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High-angle neutron diffraction was used to directly reveal the atomic-scale magnetic structure of a single-crystalline BiMn0.5Fe0.5O3 thin film deposited on a SrTiO3 (001) substrate. The BiMn0.5Fe0.5O3 phase exhibits distinctive magnetic properties that differentiate it from both parent compounds: BiFeO3 and BiMnO3. A transition to long-range G-type antiferromagnetism was observed below 120 K with a (mathmathmath) propagation vector. A weak ferromagnetic behavior was measured at low temperature by superconducting quantum interference device (SQUID) magnetometry. There is no indication of the spin cycloid, known for BiFeO3, in the BiMn0.5Fe0.5O3 thin film. The neutron diffraction suggests a random distribution of Mn and Fe over perovskite B sites.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.55.-a Thin film structure and morphology

Spin polarization of Zn1−xCoxO probed by magnetoresistance

Q. Li, T. T. Shen, Z. K. Dai, Y. L. Cao, S. S. Yan, S. S. Kang, Y. Y. Dai, Y. X. Chen, G. L. Liu, and L. M. Mei

Appl. Phys. Lett. 101, 172405 (2012); http://dx.doi.org/10.1063/1.4764542 (4 pages) | Cited 1 time

Online Publication Date: 26 October 2012

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The spin polarization of Zn0.32Co0.68O1−v (v means oxygen vacancies) concentrated magnetic semiconductor (CMS) films was extracted from measurements of tunneling magnetoresistance (TMR), and spin-dependent variable range hopping, respectively. A TMR ratio of 19.1% was observed at 2 K in Co/ZnO/Zn0.32Co0.68O1−v magnetic tunnel junctions, which gives a low limit of the spin polarization of 25% in the Zn0.32Co0.68O1−v CMS. The TMR decreases with increasing temperature and bias voltage mainly due to the tunneling via localized impurity states in the barrier. By contrast, the spin polarization of the Zn0.32Co0.68O1−v CMS was estimated to be 36.1% by spin-dependent variable range hopping.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ga II-VI semiconductors
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
71.55.Gs II-VI semiconductors
72.25.-b Spin polarized transport

Microwave assisted resonant domain wall nucleation in permalloy nanowires

Masamitsu Hayashi, Yukiko K. Takahashi, and Seiji Mitani

Appl. Phys. Lett. 101, 172406 (2012); http://dx.doi.org/10.1063/1.4764053 (4 pages)

Online Publication Date: 26 October 2012

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We have designed a system to study microwave assisted domain wall nucleation in permalloy nanowires. We find a substantial decrease in the nucleation field when microwave fields are applied, in comparison to pulse fields. A clear resonance peak is observed in the frequency dependence of the nucleation field, which coincides with the uniform mode ferromagnetic resonance frequency. Owing to the well-defined nucleation process, the switching field distribution is small in contrast to previous reports. Our results show that localized microwave field provides an efficient tool for injecting domain walls into magnetic nanowires.
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75.60.Ch Domain walls and domain structure
81.07.Gf Nanowires
75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Bb Fe and its alloys
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Quantum phase slips in superconducting Nb nanowire networks deposited on self-assembled Si templates

C. Cirillo, M. Trezza, F. Chiarella, A. Vecchione, V. P. Bondarenko, S. L. Prischepa, and C. Attanasio

Appl. Phys. Lett. 101, 172601 (2012); http://dx.doi.org/10.1063/1.4764066 (5 pages)

Online Publication Date: 24 October 2012

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Robust porous silicon substrates were employed for generating interconnected networks of superconducting ultrathin Nb nanowires. Scanning electron microscopy analysis was performed to investigate the morphology of the samples, which constitute of polycrystalline single wires with grain size of about 10 nm. The samples exhibit nonzero resistance over a broad temperature range below the critical temperature, fingerprint of phase slippage processes. The transport data are satisfactory reproduced by models describing both thermal and quantum fluctuations of the superconducting order parameter in thin homogeneous superconducting wires.
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74.40.Kb Quantum critical phenomena
74.78.Na Mesoscopic and nanoscale systems
74.10.+v Occurrence, potential candidates
73.63.Nm Quantum wires
61.43.Gt Powders, porous materials
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Poole-Frenkel emission in epitaxial nickel oxide on AlGaN/GaN heterostructures

Patrick Fiorenza, Giuseppe Greco, Filippo Giannazzo, Raffaella Lo Nigro, and Fabrizio Roccaforte

Appl. Phys. Lett. 101, 172901 (2012); http://dx.doi.org/10.1063/1.4761961 (4 pages) | Cited 1 time

Online Publication Date: 22 October 2012

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In this letter, the conduction mechanism through epitaxial nickel oxide (NiO) dielectric films grown by metal-organic chemical vapor deposition on AlGaN/GaN heterostructures was investigated. In particular, macroscopic current-voltage measurements carried out at different temperatures allowed to demonstrate that Poole-Frenkel (PF) mechanism rules the conduction through the dielectric layer, with an emission barrier of 0.2 eV. Conductive atomic force microscopic measurements were carried out to directly image the presence of preferential current spots on the NiO surface, which have been correlated to the defects responsible for the PF emission.
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73.50.Fq High-field and nonlinear effects
68.55.aj Insulators
77.84.Lf Composite materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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