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27 Jun 2011

Volume 98, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 263101 (2011); http://dx.doi.org/10.1063/1.3587576 (3 pages)

Jing Ye, Yu Zhao, Libin Tang, Li-Miao Chen, C. M. Luk, S. F. Yu, S. T. Lee, and S. P. Lau
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Composition pulling effect and strain relief mechanism in AlGaN/AlN distributed Bragg reflectors

B. Liu, R. Zhang, J. G. Zheng, X. L. Ji, D. Y. Fu, Z. L. Xie, D. J. Chen, P. Chen, R. L. Jiang, and Y. D. Zheng

Appl. Phys. Lett. 98, 261916 (2011); http://dx.doi.org/10.1063/1.3605681 (3 pages) | Cited 1 time

Online Publication Date: 30 June 2011

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We report on the composition pulling effect and strain relief mechanism in AlGaN/AlN distributed Bragg reflectors (DBRs) grown on GaN template/α-Al2O3(0001) by metal organic chemical vapor deposition. The reciprocal space mapping contours reveal that these DBRs are coherently grown. Cross-section transmission electron microscopy image of the AlGaN/AlN DBRs and the energy-dispersive x-ray analysis indicate that an AlGaN layer with gradient Al composition is located between the Al0.4Ga0.6N and AlN layers along the [0001] direction. It is attributed to the fact that Ga atoms in AlGaN are pulled and segregated to the upper layer by the strain. The density of strain energy is estimated to reduce more than one order by forming this quasi-three-sublayer structure comparing to the designed bi-sublayer structure.
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42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Raman study of strained Ge1−xSnx alloys

Hai Lin, Robert Chen, Yijie Huo, Theodore I. Kamins, and James S. Harris

Appl. Phys. Lett. 98, 261917 (2011); http://dx.doi.org/10.1063/1.3606384 (3 pages) | Cited 4 times

Online Publication Date: 30 June 2011

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The Ge-Ge longitudinal optical Raman peak has been measured in strained Ge1−xSnx alloy layers grown on top of relaxed InyGa1−yAs buffer layers on GaAs substrates by molecular beam epitaxy. The experimental result shows that the peak frequency shift increases linearly from the value for bulk Ge with the Sn fraction x and the strain ɛ, Δω = ω − ωGe = ax + bɛ. In these experiments alloy and strain contributions are decoupled and measured separately, and a and b are determined to be a = − 82 ± 4 cm−1 and b = − 563 ± 34 cm−1, over the entire composition and strain range investigated.
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78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors
68.60.Bs Mechanical and acoustical properties
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Bx Metals, semimetals, and alloys

Tunable coupling between exciton and surface plasmon in liquid crystal devices consisting of Au nanoparticles and CdSe quantum dots

Chung-Tse Chen, Chun-Chih Liu, Chun-Hsiung Wang, Chih-Wei Chen, and Yang-Fang Chen

Appl. Phys. Lett. 98, 261918 (2011); http://dx.doi.org/10.1063/1.3606539 (3 pages) | Cited 4 times

Online Publication Date: 1 July 2011

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We report controllable coupling between exciton and localized surface plasmon in a liquid crystal device consisting of gold nanoparticles and CdSe quantum dots. Through an external electric voltage, the emission wavelength of quantum dots can be manipulated. The underlying mechanism is based on the fact that by changing the dielectric index of liquid crystal with an external bias, the surface plasmon frequency of metal nanoparticles can be adjusted. It is therefore possible to control the energy difference between exciton and surface plasmon resonance, and hence to change their coupling strength. Our strategy may open up a possible route for the development of smart optoelectronic devices with tunable emission color.
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42.79.Kr Display devices, liquid-crystal devices

Rare earth doped core-shell particles as phosphor for warm-white light-emitting diodes

K. Korthout, P. F. Smet, and D. Poelman

Appl. Phys. Lett. 98, 261919 (2011); http://dx.doi.org/10.1063/1.3606540 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2011

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Light-emitting diodes (LEDs) are efficient, energy-saving light sources. Unfortunately, designing phosphors for LEDs that emit warm white light is not straightforward. We solvothermally prepared rare earth doped alkaline earth sulfides with a core-shell structure in order to obtain a physical separation between different dopants (europium and cerium). Cathodoluminescence of a single phosphor particle in an electron microscope proves simultaneous Eu2+ and Ce3+ broad band emission. The emission color can be tuned by variation of the composition, core size, and shell thickness. Upon excitation of SrS:Eu2+-SrS:Ce3+ core-shell structures at 430 nm, white light emission with good color rendering and a color temperature around 3000 K is obtained.
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85.60.Jb Light-emitting devices

Excitation spectra of ABC-stacked graphene superlattice

Chih-Wei Chiu, Yuan-Cheng Huang, Feng-Lin Shyu, and Ming-Fa Lin

Appl. Phys. Lett. 98, 261920 (2011); http://dx.doi.org/10.1063/1.3605562 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2011

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The excitation spectra of ABC-stacked graphene superlattices are calculated by the gradient approximation. Based on the selection rule, only excitations between the conduction and valence bands of the same pairs are allowed. These excitations occur at the critical points in the energy-wave vector space. Different polarization directions induce different spectra. The spectra of a parallel polarization are stronger than those of a vertical polarization. The strong electron-hole excitations cause special structures in the electron-hole excitation and reflectance spectra. However, only one plasmon peak exists in the loss spectra of the parallel polarization. Some properties are consistent with the experimental measurements.
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73.21.Cd Superlattices
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Observation of overstrain in the coalescence zone of AlAs/AlOx oxidation fronts

F. Chouchane, G. Almuneau, O. Gauthier-Lafaye, A. Monmayrant, A. Arnoult, G. Lacoste, and C. Fontaine

Appl. Phys. Lett. 98, 261921 (2011); http://dx.doi.org/10.1063/1.3606385 (3 pages)

Online Publication Date: 1 July 2011

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Strain from oxidation-induced volume shrinkage is studied by micro-photoluminescence. An InGaAs/GaAs quantum well (QW) placed at the vicinity of the selectively oxidized AlAs layer is used to probe the spatial distribution of the strain with a resolution of 1 µm. A QW wavelength shift of 1 nm imputed to the embedded strain is observed in agreement with finite element calculations. With this method, an overstrained zone is highlighted where the counter-propagative oxidation fronts merge.
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68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
78.67.De Quantum wells
81.65.Mq Oxidation
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Dramatic enhancement of thermoelectric power factor in PbTe:Cr co-doped with iodine

Biplab Paul, P. K. Rawat, and P. Banerji

Appl. Phys. Lett. 98, 262101 (2011); http://dx.doi.org/10.1063/1.3603962 (3 pages) | Cited 1 time

Online Publication Date: 27 June 2011

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We report thermoelectric properties of PbTe doubly doped with chromium (Cr) and iodine (I). Cr is found to create a local enhancement of density of states (DOS) in the conduction band of PbTe, and I is found to tune the position of the Fermi level. The coincidence of the Fermi level with the enhanced DOS is found to produce up to 135% enhancement in thermopower leading to a high power factor (PF) of 56.16 × 10−4 Wm−1K−2 at 500 K. Such high value of power factor can produce thermoelectric figure of merit (ZT) above 2.
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72.20.Pa Thermoelectric and thermomagnetic effects
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states

Electrical spin accumulation with improved bias voltage dependence in a crystalline CoFe/MgO/Si system

Kun-Rok Jeon, Byoung-Chul Min, Il-Jae Shin, Chang-Yup Park, Hun-Sung Lee, Young-Hun Jo, and Sung-Chul Shin

Appl. Phys. Lett. 98, 262102 (2011); http://dx.doi.org/10.1063/1.3600787 (3 pages) | Cited 11 times

Online Publication Date: 27 June 2011

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We report the electrical spin accumulation with enhanced bias voltage dependence in n-type Si, employing a crystalline CoFe/MgO tunnel contact. A sizable spin signal of ∼4.8 kΩμm2, a spin lifetime of ∼155 ps, and a spin diffusion length of ∼220 nm were obtained at 300 K. The spin signal and lifetime obtained in this system show consistent behavior with the temperature variation irrespective of the bias voltage. Notably, the spin signal exhibits nearly symmetric dependence with respect to the bias polarity, which is ascribed to the improved bias dependence of tunnel spin polarization.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.25.-b Spin polarized transport

Chemical vapor deposition-assembled graphene field-effect transistor on hexagonal boron nitride

Edwin Kim, Tianhua Yu, Eui Sang Song, and Bin Yu

Appl. Phys. Lett. 98, 262103 (2011); http://dx.doi.org/10.1063/1.3604012 (3 pages) | Cited 2 times

Online Publication Date: 28 June 2011

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We investigate key electrical properties of monolayer graphene assembled by chemical vapor deposition (CVD). Graphene field-effect transistors (GFETs) were fabricated with carbon channel placing directly on hexagonal boron nitride (h-BN) and SiO2. Small-signal transconductance (gm) and effective carrier mobility (μeff) are improved by 8.5 and 4 times on h-BN, respectively, as compared with that on SiO2. Compared with GFET with exfoliated graphene on SiO2, gm and μeff measured from device with CVD graphene on h-BN substrate exhibit comparable values. The experiment demonstrates the potential of employing h-BN as a platform material for large-area carbon electronics.
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85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors

The metallic interface between the two band insulators LaGaO3 and SrTiO3

S. Nazir, N. Singh, and U. Schwingenschlögl

Appl. Phys. Lett. 98, 262104 (2011); http://dx.doi.org/10.1063/1.3604020 (3 pages) | Cited 3 times

Online Publication Date: 28 June 2011

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The formation of metallic interface states between the two band insulators LaGaO3 and SrTiO3 is studied by the full-potential linearized augmented plane-wave method based on density functional theory. Structural optimization of the atomic positions points to only small changes of the chemical bonding at the interface. The n-type (LaO/TiO2) and p-type (GaO2/SrO) interfaces turn out to be metallic. Reduction of the O content increases the conductivity of the n-type interface, while the p-type interface can be turned gradually from a hole doped into an electron doped state.
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73.20.At Surface states, band structure, electron density of states
68.35.Ct Interface structure and roughness
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Characterization of a microwave frequency resonator via a nearby quantum dot

T. Frey, P. J. Leek, M. Beck, K. Ensslin, A. Wallraff, and T. Ihn

Appl. Phys. Lett. 98, 262105 (2011); http://dx.doi.org/10.1063/1.3604784 (3 pages)

Online Publication Date: 28 June 2011

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We present measurements of a hybrid system consisting of a microwave transmission-line resonator and a lateral quantum dot defined on a GaAs heterostructure. The two subsystems are separately characterized and their interaction is studied by monitoring the electrical conductance through the quantum dot. The presence of a strong microwave field in the resonator is found to reduce the resonant conductance through the quantum dot and is attributed to electron heating and modulation of the dot potential. We use this interaction to demonstrate a measurement of the resonator transmission spectrum using the quantum dot.
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84.40.Az Waveguides, transmission lines, striplines

Formation of a semi-insulating layer in n-type 4H-SiC by electron irradiation

Hiromi Kaneko and Tsunenobu Kimoto

Appl. Phys. Lett. 98, 262106 (2011); http://dx.doi.org/10.1063/1.3604795 (3 pages) | Cited 2 times

Online Publication Date: 29 June 2011

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Electron irradiation has been applied to the formation of a semi-insulating 4H-SiC(0001) layer. The resistivity of the semi-insulating layer, which was irradiated with a fluence of 1.9 × 1018 cm−2 at 400 keV, exceeded 1010 Ω cm at room temperature. From capacitance-voltage characteristics of Schottky structure, the depth of the semi-insulating layer was estimated to be 10 μm, indicating that the whole region of lightly-doped n-type epilayer was converted to the semi-insulating layer by electron irradiation. The semi-insulating property can be ascribed to electron trapping at the Z1/2 and EH6/7 centers generated by electron irradiation. The threshold energy for the generation of Z1/2 center was about 100 keV.
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68.55.ag Semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.30.+y Surface double layers, Schottky barriers, and work functions
61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors
73.61.Le Other inorganic semiconductors

Trigonal distortion of topologically confined channels in bilayer graphene

A. S. Núñez, E. Suárez Morell, and P. Vargas

Appl. Phys. Lett. 98, 262107 (2011); http://dx.doi.org/10.1063/1.3605568 (3 pages) | Cited 1 time

Online Publication Date: 29 June 2011

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In this work, we show that the trigonal warping of the electronic bands in bilayer graphene dramatically modifies the behavior of the topologically confined one-dimensional modes due to an inhomogeneous bias that changes sign across a channel. Up to four zero modes are present, depending on the orientation of the channel, these zero modes are related to a fractionalization of the topological charge due to the trigonal warping.
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81.05.ue Graphene
73.22.Pr Electronic structure of graphene

On the effect of Ti on the stability of amorphous indium zinc oxide used in thin film transistor applications

Sunghwan Lee and David C. Paine

Appl. Phys. Lett. 98, 262108 (2011); http://dx.doi.org/10.1063/1.3605589 (3 pages) | Cited 3 times

Online Publication Date: 30 June 2011

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In2O3-based amorphous oxide channel materials are of increasing interest for thin film transisitor applications due, in part, to the remarkable stability of this class of materials amorphous structure and electronic properties. We report that this stability is degraded in the presence of Ti, which is widely used as a contact and/or adhesion layer. A cross-sectional transmission electron microscopy analysis, supported by glancing incident angle x-ray and selected area diffraction examination, shows that amorphous indium zinc oxide in contact with Ti undergoes crystallization to the bixbyite phase and reacts to form the rutile phase of TiO2 at a temperature of 200 °C. A basic thermodynamic analysis is presented and forms the basis of a model that describes both the crystallization and the resistivity decrease.
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85.30.Tv Field effect devices
81.05.Gc Amorphous semiconductors
88.05.De Thermodynamic constraints on energy production
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Improved tunneling magnetoresistance in (Ga,Mn)As/AlOx/CoFeB magnetic tunnel junctions

G. Q. Yu, L. Chen, Syed Rizwan, J. H. Zhao, K. XU, and X. F. Han

Appl. Phys. Lett. 98, 262501 (2011); http://dx.doi.org/10.1063/1.3603946 (3 pages)

Online Publication Date: 27 June 2011

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We fabricated (Ga,Mn)As/AlOx/Co40Fe40B20 magnetic tunnel junctions with ferromagnetic semiconductor/insulator/ferromagnetic metal (S/I/F) structure. The treatments of pre-annealing and post-plasma cleaning on the (Ga,Mn)As film were introduced before the growth of the subsequent layers. A high tunneling magnetoresistance (TMR) ratio of 101% is achieved at 2 K, and the spin polarization of (Ga,Mn)As, P = 56.8%, is deduced from Jullière’s formula. The improved TMR ratio is primarily due to the improved magnetism of (Ga,Mn)As layer by low-temperature annealing and cleaned interface between (Ga,Mn)As and AlOx attained by subsequent plasma cleaning process.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.25.Mk Spin transport through interfaces
81.05.Ea III-V semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Bb Fe and its alloys
75.50.Dd Nonmetallic ferromagnetic materials

Ferrohydrodynamic relaxometry for magnetic particle imaging

P. W. Goodwill, A. Tamrazian, L. R. Croft, C. D. Lu, E. M. Johnson, R. Pidaparthi, R. M. Ferguson, A. P. Khandhar, K. M. Krishnan, and S. M. Conolly

Appl. Phys. Lett. 98, 262502 (2011); http://dx.doi.org/10.1063/1.3604009 (3 pages) | Cited 3 times

Online Publication Date: 27 June 2011

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The ferrohydrodynamic properties of magnetic nanoparticles govern resolution and signal strength in magnetic particle imaging (MPI), a medical imaging modality with applications in small animals and humans. Here, we discuss the development and key results of a magnetic particle relaxometer that measures the core diameter and relaxation constant of magnetic nanoparticles. This instrument enables us to directly measure the one-dimensional MPI point spread function. To elucidate our results, we develop a simplified ferrohydrodynamic model that assumes nanoparticles respond to time varying magnetic fields according to a Debeye model of Brownian relaxation, which we verify with experimental data.
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87.85.Pq Biomedical imaging
87.85.Rs Nanotechnologies-applications
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.Jn Dynamics of magnetic nanoparticles
47.65.Cb Magnetic fluids and ferrofluids

Local and non-local magnetoresistance with spin precession in highly doped Si

T. Sasaki, T. Oikawa, T. Suzuki, M. Shiraishi, Y. Suzuki, and K. Noguchi

Appl. Phys. Lett. 98, 262503 (2011); http://dx.doi.org/10.1063/1.3604010 (3 pages) | Cited 1 time

Online Publication Date: 28 June 2011

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We have demonstrated comparison of spin accumulation voltages in local and non-local (NL) magnetoresistance measurements without any spurious megnetoresistive signals. The spin transport length in a local measurement was larger than that in a NL measurement. An intensity of the local signals was explained by a conductivity mismatch theory. Depending on the relative magnetic configurations, Hanle-type spin precession signals in the local and the NL schemes showed a clear difference in signal shapes. The local transporting spins are accelerated in the direction of the electric field, and precess around the direction of the magnetic field under the detector electrode.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Cw Elemental semiconductors
72.25.Dc Spin polarized transport in semiconductors

Electrical control of reversible and permanent magnetization reorientation for magnetoelectric memory devices

Tao Wu (吴涛), Alexandre Bur, Kin Wong, Ping Zhao, Christopher S. Lynch, Pedram Khalili Amiri, Kang L. Wang, and Gregory P. Carman

Appl. Phys. Lett. 98, 262504 (2011); http://dx.doi.org/10.1063/1.3605571 (3 pages) | Cited 10 times

Online Publication Date: 30 June 2011

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We report giant reversible and permanent magnetic anisotropy reorientation between two perpendicular easy axes in a magnetoelectric polycrystalline Ni thin film and (011) oriented [Pb(Mg1/3Nb2/3)O3](1−x)-[PbTiO3]x (PMN-PT) heterostructure. The PMN-PT is partially poled prior to Ni film deposition to provide a remanent strain bias. Following Ni deposition and full poling of the sample, two giant remanent strains of equal and opposite values are used to reversibly and permanently reorient the magnetization state of the Ni film. These experimental results are integrated into micromagnetic simulation to demonstrate the usefulness of this approach for magnetoelectric based magnetic random access memory.
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75.30.Gw Magnetic anisotropy
77.55.Nv Multiferroic/magnetoelectric films
75.85.+t Magnetoelectric effects, multiferroics

Epitaxial growth of Heusler alloy Co2MnSi/MgO heterostructures on Ge(001) substrates

Gui-fang Li, Tomoyuki Taira, Ken-ichi Matsuda, Masashi Arita, Tetsuya Uemura, and Masafumi Yamamoto

Appl. Phys. Lett. 98, 262505 (2011); http://dx.doi.org/10.1063/1.3605675 (3 pages) | Cited 1 time

Online Publication Date: 30 June 2011

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We prepared Heusler alloy Co2MnSi/MgO heterostructures on single-crystal Ge(001) substrates through magnetron sputtering for Co2MnSi and electron beam evaporation for MgO as a promising candidate for future generation spin-based functional devices. Structural investigations showed that the Co2MnSi/MgO heterostructure was grown epitaxially on a Ge(001) substrate with extremely smooth and abrupt interfaces and showed the L21 structure for the Co2MnSi film. Furthermore, a sufficiently high saturation magnetization (μs) value of 5.1 µB/f.u. at 10 K, which is close to the theoretically predicted μs of 5.0 µB/f.u. for half-metallic Co2MnSi, was obtained for prepared Co2MnSi films.
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81.15.Cd Deposition by sputtering
81.15.Dj E-beam and hot filament evaporation deposition
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.A- Nucleation and growth

Temperature-dependent magnetic anisotropies in epitaxial Fe/CoO/MgO(001) system studied by the planar Hall effect

W. N. Cao, J. Li, G. Chen, J. Zhu, C. R. Hu, and Y. Z. Wu

Appl. Phys. Lett. 98, 262506 (2011); http://dx.doi.org/10.1063/1.3606531 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2011

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Exchange-induced in-plane magnetic anisotropies in a single-crystalline Fe/CoO/MgO(001) system were quantitatively investigated using the planar Hall effect as a function of temperature. Field cooling can induce a strong uniaxial anisotropy in Fe film with the easy axis along the CoO〈110〉 directions close to the cooling field direction. The exchange coupling also induces a 4-fold anisotropy with the easy axis along the CoO〈100〉 directions. Our results prove that the strong magneto-crystalline anisotropy of CoO antiferromagnetic spin plays a significant role in exchange-induced anisotropy.
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75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions

Direct probing magnetization reversal of exchange-coupled-composite media by x-ray magnetic circular dichroism

Hao-Cheng Hou, Dieter Suess, Jung-Wei Liao, Meng-Shian Lin, Hong-Ji Lin, Fan-Hsiu Chang, and Chih-Huang Lai

Appl. Phys. Lett. 98, 262507 (2011); http://dx.doi.org/10.1063/1.3603945 (3 pages) | Cited 3 times

Online Publication Date: 1 July 2011

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X-ray magnetic circular dichroism (XMCD) was used to directly probe the depth-dependent magnetization reversal of CoPtCr-SiO2-based exchange-coupled-composite media with laminated soft layers. A thin Fe-marker layer in the soft layer was used as the indicator of local magnetization. Element-specific XMCD loops of Fe-marker layers confirmed the transition of the magnetization reversal from rigid magnets to exchange-spring magnets with increasing thickness of the soft layer. The micromagnetic simulations revealed the importance of the reduced exchange constant (Asoft) by laminating the soft layer for domain-wall assisting reversal. By comparing XMCD loops with simulations, we can deduce the effective Asoft.
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75.60.Jk Magnetization reversal mechanisms
75.78.Cd Micromagnetic simulations
78.20.Ls Magneto-optical effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Field tunable localization of spin waves in antidot arrays

C.-L. Hu, R. Magaraggia, H.-Y. Yuan, C. S. Chang, M. Kostylev, D. Tripathy, A. O. Adeyeye, and R. L. Stamps

Appl. Phys. Lett. 98, 262508 (2011); http://dx.doi.org/10.1063/1.3606556 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2011

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We show that magnetic spin wave resonance modes in an antidot patterned array are sensitive to small changes in the magnetic configuration near dots, resulting in strong localization effects as the field is increased. Frequencies measured using ferromagnetic resonance from an antidot array patterned from a NiFe/IrMn bilayer are interpreted using micromagnetic calculations, and it is shown that the observed field dependence of the resonance response can be attributed to strong interdot localization of spin waves. This field tunable localization is created by stray fields produced by magnetic poles at the dot surfaces.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.78.Cd Micromagnetic simulations
75.75.-c Magnetic properties of nanostructures

Iron-chalcogenide FeSe0.5Te0.5 coated superconducting tapes for high field applications

Weidong Si, Juan Zhou, Qing Jie, Ivo Dimitrov, V. Solovyov, P. D. Johnson, J. Jaroszynski, V. Matias, C. Sheehan, and Qiang Li

Appl. Phys. Lett. 98, 262509 (2011); http://dx.doi.org/10.1063/1.3606557 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2011

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The high upper critical field characteristic of the recently discovered iron-based superconducting chalcogenides opens the possibility of developing a new type of non-oxide high-field superconducting wires. In this work, we utilize a buffered metal template on which we grow a textured FeSe0.5Te0.5 layer, an approach developed originally for high temperature superconducting coated conductors. These tapes carry high critical current densities (>1 × 104 A/cm2) at about 4.2 K under magnetic field as high as 25 T, which are nearly isotropic to the field direction. This demonstrates a very promising future for iron chalcogenides for high field applications at liquid helium temperatures. Flux pinning force analysis indicates a point defect pinning mechanism, creating prospects for a straightforward approach to conductor optimization.
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84.71.Mn Superconducting wires, fibers, and tapes
74.25.Wx Vortex pinning (includes mechanisms and flux creep)
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Improved endurance of resistive switching TiO2 thin film by hourglass shaped Magnéli filaments

Gun Hwan Kim, Jong Ho Lee, Jun Yeong Seok, Seul Ji Song, Jung Ho Yoon, Kyung Jean Yoon, Min Hwan Lee, Kyung Min Kim, Hyung Dong Lee, Seung Wook Ryu, Tae Joo Park, and Cheol Seong Hwang

Appl. Phys. Lett. 98, 262901 (2011); http://dx.doi.org/10.1063/1.3600784 (3 pages) | Cited 5 times

Online Publication Date: 27 June 2011

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A modified biasing scheme was adopted to improve the electrical endurance characteristics of conducting filamentary resistive switching (RS) in a Pt/TiO2/Pt RS cell. The modified bias scheme included the application of bias voltages with alternating polarity, even though RS proceeds in non-polar mode, which results in the stable distribution of each resistance states as well as improved endurance. This was attributed to the minimized consumption of oxygen ions in the TiO2 film, which can be induced by the formation of hourglass-shaped conducting filament (HSCF). The presence of a HSCF was confirmed by high-resolution transmission electron microscopy.
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73.40.Ns Metal-nonmetal contacts
73.61.-r Electrical properties of specific thin films
68.37.Og High-resolution transmission electron microscopy (HRTEM)
72.60.+g Mixed conductivity and conductivity transitions

3.4 GHz composite thin film bulk acoustic wave resonator for miniaturized atomic clocks

Alvaro Artieda and Paul Muralt

Appl. Phys. Lett. 98, 262902 (2011); http://dx.doi.org/10.1063/1.3603944 (3 pages)

Online Publication Date: 28 June 2011

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Triple layer SiO2/AlN/SiO2 composite thin film bulk acoustic wave resonators (TFBARs) were studied for applications in atomic clocks. The TFBAR’s were tuned to 3.4 GHz, corresponding to half the hyperfine splitting of the ground state of rubidium 87Rb atoms. The quality factor (Q) was equal to 2300 and the temperature coefficient of the resonance frequency fr amounted to 1.5 ppm/K. A figure of merit Qfr of ∼ 0.8 × 1013 Hz and a thickness mode coupling factor of 1% were reached. Such figures are ideal for frequency sources in an oscillator circuit that tracks the optical signal in atomic clocks.
Show PACS
43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators
06.30.Ft Time and frequency
06.20.F- Units and standards
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