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24 Sep 2012

Volume 101, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 133101 (2012); http://dx.doi.org/10.1063/1.4752467 (5 pages)

Yen Husn Su and Wei-Yu Chen
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A modified Weibull model for tensile strength distribution of carbon nanotube fibers with strain rate and size effects

Gengzhi Sun, John H. L. Pang, Jinyuan Zhou, Yani Zhang, Zhaoyao Zhan, and Lianxi Zheng

Appl. Phys. Lett. 101, 131905 (2012); http://dx.doi.org/10.1063/1.4754709 (4 pages) | Cited 1 time

Online Publication Date: 25 September 2012

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Fundamental studies on the effects of strain rate and size on the distribution of tensile strength of carbon nanotube (CNT) fibers are reported in this paper. Experimental data show that the mechanical strength of CNT fibers increases from 0.2 to 0.8 GPa as the strain rate increases from 0.00001 to 0.1 (1/s). In addition, the influence of fiber diameter at low and high strain rate conditions was investigated further with statistical analysis. A modified Weibull distribution model for characterizing the tensile strength distribution of CNT fibers taking into account the effect of strain rate and fiber diameter is proposed.
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81.40.Lm Deformation, plasticity, and creep
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
62.20.F- Deformation and plasticity
62.25.-g Mechanical properties of nanoscale systems
61.46.Fg Nanotubes

Fabrication and photoluminescence of SiC quantum dots stemming from 3C, 6H, and 4H polytypes of bulk SiC

Jiyang Fan, Hongxia Li, Jing Wang, and Min Xiao

Appl. Phys. Lett. 101, 131906 (2012); http://dx.doi.org/10.1063/1.4755778 (5 pages)

Online Publication Date: 25 September 2012

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We report the fabrication and photoluminescence properties of the colloidal SiC quantum dots (QDs) stemming, respectively, from diminishing different polytypes (3C, 6H, and 4H) of bulk SiC crystals using electrochemical method. The three types of obtained SiC QDs show unexpected quite-similar photoluminescence, photoluminescence excitation, and transient photoluminescence properties. This strange phenomenon is explained by using the polytypic transformations of the colloidal SiC QDs driven by ultrasonic waves. Our results will greatly deepen our understanding of the fundamental physics of nanoscale SiC.
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78.67.Hc Quantum dots
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
82.70.Dd Colloids
82.80.Fk Electrochemical methods
64.70.K- Solid-solid transitions
78.55.Hx Other solid inorganic materials

Role of nucleation sites on the formation of nanoporous Ge

B. R. Yates, B. L. Darby, R. G. Elliman, and K. S. Jones

Appl. Phys. Lett. 101, 131907 (2012); http://dx.doi.org/10.1063/1.4755886 (4 pages) | Cited 3 times

Online Publication Date: 26 September 2012

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The role of nucleation sites on the formation of nanoporous Ge was investigated. Three Ge films with different spherical or columnar pore morphologies to act as inherent nucleation sites were sputtered on (001) Ge. Samples were implanted 90° from incidence at 300 keV with fluences ranging from 3.0 × 1015 to 3.0 × 1016 Ge+/cm2. Electron microscopy investigations revealed varying thresholds for nanoporous Ge formation and exhibited a stark difference in the evolution of the Ge layers based on the microstructure of the initial film. The results suggest that the presence of inherent nucleation sites significantly alters the onset and evolution of nanoporous Ge.
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61.43.Gt Powders, porous materials
61.82.Rx Nanocrystalline materials
68.47.Fg Semiconductor surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.bg Semiconductors
68.55.ag Semiconductors

Fabrication and performance optimization of the magneto-optical (Tb1−xRx)3Al5O12 (R = Y, Ce) transparent ceramics

Chong Chen, Shengming Zhou, Hui Lin, and Qing Yi

Appl. Phys. Lett. 101, 131908 (2012); http://dx.doi.org/10.1063/1.4756789 (4 pages)

Online Publication Date: 28 September 2012

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(Tb1−xRx)3Al5O12 (R = Y, Ce) magneto-optical transparent ceramics were synthesized by solid state reaction and vacuum sintering. The two-step sintering method was also applied to investigate the properties of the Y3+ doped Tb3Al5O12 samples. The Verdet constant of the Y3+ doped Tb3Al5O12 transparent ceramic measured at 632.8 nm was −108.79 rad · T−1 · m−1, which was smaller than that of the Tb3Al5O12 transparent ceramics. However, the magneto-optical property of the Ce3+ doped Tb3Al5O12 samples was improved a lot. The Verdet constant measured at 632.8 nm was −199.55 rad · T−1 · m−1, which was about 16% larger than that of Tb3Al5O12.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.72.up Other materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Ls Magneto-optical effects

Condensation heat transfer on two-tier superhydrophobic surfaces

Jiangtao Cheng, Aref Vandadi, and Chung-Lung Chen

Appl. Phys. Lett. 101, 131909 (2012); http://dx.doi.org/10.1063/1.4756800 (4 pages) | Cited 3 times

Online Publication Date: 28 September 2012

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We investigated water vapor condensation on a two-tier superhydrophobic surface in an environmental scanning electron microscope (ESEM) and in a customer-designed vapor chamber. We have observed continuous dropwise condensation (DWC) on the textured surface in ESEM. However, a film layer of condensate was formed on the multiscale texture in the vapor chamber. Due to the filmwise condensation, the condensation heat transfer coefficient of the superhydrophobic surface is lower than that of a flat hydrophobic surface especially under high heat flux situations. Our studies indicate that adaptive and prompt condensate droplet purging is the dominant factor for sustaining long-term DWC.
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68.03.Fg Evaporation and condensation of liquids
68.15.+e Liquid thin films
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Strain dependent stabilization of metallic paramagnetic state in epitaxial NdNiO3 thin films

Yogesh Kumar, R. J. Choudhary, S. K. Sharma, M. Knobel, and Ravi Kumar

Appl. Phys. Lett. 101, 132101 (2012); http://dx.doi.org/10.1063/1.4754593 (5 pages)

Online Publication Date: 24 September 2012

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We report here the strain dependent study of epitaxial NdNiO3 films deposited on LaAlO3 and SrTiO3 substrates using pulsed laser deposition. Electrical transport and magnetic properties of films are found to be controlled by the substrate induced strain. NdNiO3 film on SrTiO3 substrate exhibits behaviour similar to that of bulk NdNiO3, while stabilization of low temperature metallic paramagnetic phase has been observed for film deposited on LaAlO3 substrate. Invariance of Raman spectra, with temperature, of the film on LaAlO3 reveals that the melting of charge ordering under compressive strain is responsible for the stabilization of metallic phase at lower temperature.
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68.60.Bs Mechanical and acoustical properties
73.61.Ng Insulators
75.20.Ck Nonmetals
75.70.Ak Magnetic properties of monolayers and thin films
78.30.Hv Other nonmetallic inorganics
81.15.Fg Pulsed laser ablation deposition

Suppression of m-plane and c-plane slip through Si and Mg doping in partially relaxed (20math1) InGaN/GaN heterostructures

Matthew T. Hardy, Erin C. Young, Po Shan Hsu, Daniel A. Haeger, Ingrid L. Koslow, Shuji Nakamura, Steven P. DenBaars, and James S. Speck

Appl. Phys. Lett. 101, 132102 (2012); http://dx.doi.org/10.1063/1.4754693 (4 pages) | Cited 2 times

Online Publication Date: 24 September 2012

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Several series of (20math1) oriented InGaN/GaN heterostructures were grown to examine the impact of Si and Mg doping on stress relaxation by misfit dislocation formation. Si doping greatly reduced m-plane slip misfit dislocation lines as observed in cathodoluminescence, as well as reducing relaxation from c-plane slip as measured using x-ray diffraction reciprocal space maps. However, samples with the same degree of relaxation still showed reduced m-plane slip for the highly Si doped case. Mg doping showed a similar effect while experiments with Si–Mg co-doping reversed the effect.
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61.72.uj III-V and II-VI semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.60.Hk Cathodoluminescence, ionoluminescence
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.sd Impurity concentration

Enhanced thermoelectric performance through energy-filtering effects in nanocomposites dispersed with metallic particles

M. Liu and X. Y. Qin

Appl. Phys. Lett. 101, 132103 (2012); http://dx.doi.org/10.1063/1.4755768 (4 pages)

Online Publication Date: 24 September 2012

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The thermoelectric properties of semiconductor materials with metallic nanoinclusions were investigated by using the Boltzmann transport equation under the relaxation time approximation. The results showed that the Seebeck coefficient can be significantly enhanced due to interface potential barrier induced by metallic nanoinclusions, leading to the optimized power factor at T < 700 K as barrier height is around kBT larger than the Fermi energy (here, kB is the Boltzmann constant). Additionally, it was found that high-concentration nanoinclusions with radius 1–2 nm can effectively enhance the thermoelectric performance of nanocomposites through energy-selective carrier scattering.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.63.Bd Nanocrystalline materials

Highly conductive p-type amorphous oxides from low-temperature solution processing

Jinwang Li (李金望), Eisuke Tokumitsu (徳光永輔), Mikio Koyano (小矢野幹夫), Tadaoki Mitani (三谷忠興), and Tatsuya Shimoda (下田達也)

Appl. Phys. Lett. 101, 132104 (2012); http://dx.doi.org/10.1063/1.4754608 (4 pages)

Online Publication Date: 26 September 2012

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We report solution-processed, highly conductive (resistivity 1.3–3.8 mΩ cm), p-type amorphous A-B-O (A = Bi, Pb; B = Ru, Ir), processable at temperatures (down to 240 °C) that are compatible with plastic substrates. The film surfaces are smooth on the atomic scale. Bi-Ru-O was analyzed in detail. A small optical bandgap (0.2 eV) with a valence band maximum (VBM) below but very close to the Fermi level (binding energy EVBM = 0.04 eV) explains the high conductivity and suggests that they are degenerated semiconductors. The conductivity changes from three-dimensional to two-dimensional with decreasing temperature across 25 K.
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73.61.Jc Amorphous semiconductors; glasses
78.66.Jg Amorphous semiconductors; glasses
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

Pronounced Purcell enhancement of spontaneous emission in CdTe/ZnTe quantum dots embedded in micropillar cavities

T. Jakubczyk, W. Pacuski, T. Smoleński, A. Golnik, M. Florian, F. Jahnke, C. Kruse, D. Hommel, and P. Kossacki

Appl. Phys. Lett. 101, 132105 (2012); http://dx.doi.org/10.1063/1.4754078 (4 pages) | Cited 1 time

Online Publication Date: 26 September 2012

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The coupling of CdTe/ZnTe quantum dot (QD) emission to micropillar cavity eigenmodes in the weak coupling regime is demonstrated. We analyze photoluminescence spectra of QDs embedded in monolithic micropillar cavities based on Bragg mirrors which contain MgSe/ZnTe/MgTe superlattices as low-index material. The pillar emission shows pronounced cavity eigenmodes, and their spectral shape is in good agreement with simulations. QD emission in resonance with the cavity mode is shown to be efficiently guided toward the detector, and an experimental Purcell enhancement by a factor of 5.7 is determined, confirming theoretical expectations.
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78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.05.Dz II-VI semiconductors
81.07.Ta Quantum dots

Schottky barrier height of Au on the transparent semiconducting oxide β-Ga2O3

M. Mohamed, K. Irmscher, C. Janowitz, Z. Galazka, R. Manzke, and R. Fornari

Appl. Phys. Lett. 101, 132106 (2012); http://dx.doi.org/10.1063/1.4755770 (5 pages)

Online Publication Date: 26 September 2012

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The Schottky barrier height of Au deposited on (100) surfaces of n-type β-Ga2O3 single crystals was determined by current-voltage characteristics and high-resolution photoemission spectroscopy resulting in a common effective value of 1.04 ± 0.08 eV. Furthermore, the electron affinity of β-Ga2O3 and the work function of Au were determined to be 4.00 ± 0.05 eV and 5.23 ± 0.05 eV, respectively, yielding a barrier height of 1.23 eV according to the Schottky-Mott rule. The reduction of the Schottky-Mott barrier to the effective value was ascribed to the image-force effect and the action of metal-induced gap states, whereas extrinsic influences could be avoided.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Sx Metal-semiconductor-metal structures
79.60.Bm Clean metal, semiconductor, and insulator surfaces

15% efficient Cu(In,Ga)Se2 solar cells obtained by low-temperature pulsed electron deposition

S. Rampino, N. Armani, F. Bissoli, M. Bronzoni, D. Calestani, M. Calicchio, N. Delmonte, E. Gilioli, E. Gombia, R. Mosca, L. Nasi, F. Pattini, A. Zappettini, and M. Mazzer

Appl. Phys. Lett. 101, 132107 (2012); http://dx.doi.org/10.1063/1.4755772 (4 pages) | Cited 3 times

Online Publication Date: 26 September 2012

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An approach to low-cost production of Cu(In,Ga)Se2 (CIGS) solar cells based on pulsed electron deposition (PED) has achieved a crucial milestone. Lab-scale solar cells with efficiencies exceeding 15% were obtained by depositing CIGS from a stoichiometric quaternary target at 270 °C and without any post-growth treatment. An effective control of the p-doping level in CIGS was achieved by starting the PED deposition with a layer of NaF tailored to generate the optimum Na diffusion. These results show that PED is a promising technology for the development of a competitive low-cost production process for CIGS solar cells.
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88.40.H- Solar cells (photovoltaics)
61.66.Bi Elemental solids
61.66.Dk Alloys
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth

Anomalous behavior of epitaxial indium nano-contacts on cadmium-zinc-telluride

A. Ruzin, O. Sinkevich, G. Cohen-Taguri, and I. Goldfarb

Appl. Phys. Lett. 101, 132108 (2012); http://dx.doi.org/10.1063/1.4754706 (4 pages)

Online Publication Date: 28 September 2012

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In this work, experimental characterization results of indium nano-contacts are presented. The indium nano-contacts are epitaxially grown on a two-dimensional surface of high-resistivity, n-type Cd0.9Zn0.1Te in ultra-high vacuum. The scaling effect in these contacts is systematic, but not linear. It is shown that the contacts exhibit a profoundly asymmetric behavior. It is argued that the “rectifying” behavior of these contacts is due to tunneling and that the tunneling does not necessarily imply Schottky nature.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
73.40.Gk Tunneling

High electron mobility through the edge states in random networks of c-axis oriented wedge-shaped GaN nanowalls grown by molecular beam epitaxy

H. P. Bhasker, S. Dhar, A. Sain, Manoj Kesaria, and S. M. Shivaprasad

Appl. Phys. Lett. 101, 132109 (2012); http://dx.doi.org/10.1063/1.4755775 (5 pages)

Online Publication Date: 28 September 2012

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Transport and optical properties of random networks of c-axis oriented wedge-shaped GaN nanowalls grown spontaneously on c-plane sapphire substrates through molecular beam epitaxy are investigated. Our study suggests a one dimensional confinement of carriers at the top edges of these connected nanowalls, which results in a blue shift of the band edge luminescence, a reduction of the exciton-phonon coupling, and an enhancement of the exciton binding energy. Not only that, the yellow luminescence in these samples is found to be completely suppressed even at room temperature. All these changes are highly desirable for the enhancement of the luminescence efficiency of the material. More interestingly, the electron mobility through the network is found to be significantly higher than that is typically observed for GaN epitaxial films. This dramatic improvement is attributed to the transport of electrons through the edge states formed at the top edges of the nanowalls.
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73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
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Positive exchange bias and upward magnetic relaxation in a Fe-film/CoO-nanoparticle hybrid system

Wei Zhang, Tianlong Wen, and Kannan M. Krishnan

Appl. Phys. Lett. 101, 132401 (2012); http://dx.doi.org/10.1063/1.4754610 (5 pages) | Cited 1 time

Online Publication Date: 24 September 2012

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Unusual positive exchange bias found in Fe/CoOx nanoparticle bilayer films is correlated to a characteristic magnetic spin-glass (SG) in CoOx, with the SG magnetization coupled antiparallel with the Fe magnetization upon field cooling. This SG magnetization has strong field- and time-dependence which displays unusual upward magnetic relaxation behavior in thermoremanent magnetization measurements. The antiparallel coupling is shown to result predominantly from the antiferromagnetic superexchange of the Fe2+-O-Co3+ couple, of the oxygen-terminated CoOx at the interface. These experimental results reveal the possibility of manipulating the exchange bias effect via an indirect exchange coupling mechanism.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
75.30.Et Exchange and superexchange interactions
75.50.Lk Spin glasses and other random magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Interplay between intrinsic and stacking-fault magnetic domains in bi-layered manganites

M. A. Hossain, Mark H. Burkhardt, S. Sarkar, H. Ohldag, Y.-D. Chuang, A. Scholl, A. T. Young, A. Doran, D. S. Dessau, H. Zheng, J. F. Mitchell, H. A. Dürr, and J. Stöhr

Appl. Phys. Lett. 101, 132402 (2012); http://dx.doi.org/10.1063/1.4754618 (4 pages)

Online Publication Date: 24 September 2012

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We present a low temperature x-ray photoemission electron microscopy study of the bi-layered manganite compound La1.2Sr1.8Mn2O7 (BL-LSMO) to investigate the influence of stacking faults, which are structurally and magnetically different from the bi-layered host. In BL-LSMO, small magnetic moment persists to T* = 300 K, well above the Curie temperature of 120 K (TC). Our magnetic images show that 3D stacking faults are responsible for the T* transition. Furthermore, close to the TC, stacking faults are well coupled to the bi-layered host with latter magnetic domains controlling the spin direction of the stacking faults. Contrary to recent reports, we find that stacking faults do not seed magnetic domains in the host via an exchange spring mechanism and the intrinsic TC of the BL-LSMO is not lower than 120 K.
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75.60.Ch Domain walls and domain structure
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.Nn Stacking faults and other planar or extended defects
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Field-controllable exchange bias in epitaxial Fe films grown on GaAs

Seonghoon Choi, Taehee Yoo, S. Khym, Sanghoon Lee, X. Liu, and J. K. Furdyna

Appl. Phys. Lett. 101, 132403 (2012); http://dx.doi.org/10.1063/1.4754622 (4 pages)

Online Publication Date: 24 September 2012

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We report that exchange bias observed in epitaxial Fe films grown on GaAs (001) substrates can be controlled by the direction of the cooling field. The effect is investigated by measuring the shift of field-cooled hysteresis loops toward specific field directions, as revealed by field scans of the planar Hall resistance at 3 K. The value of the unidirectional magnetic anisotropy corresponding to such field-controllable exchange is obtained from the angular dependence of the planar Hall effect.
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75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
72.15.Gd Galvanomagnetic and other magnetotransport effects

Detection of spin-orbit coupling of surface electron layer via reciprocal spin Hall effect in InN films

F. H. Mei, N. Tang, X. Q. Wang, J. X. Duan, S. Zhang, Y. H. Chen, W. K. Ge, and B. Shen

Appl. Phys. Lett. 101, 132404 (2012); http://dx.doi.org/10.1063/1.4754626 (4 pages)

Online Publication Date: 24 September 2012

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Swirly photocurrent in InN films arising from reciprocal spin Hall effect (RSHE) is observed under normal incidence of circularly polarized light at room temperature. It is found that the swirly current is a superposition of the RSHE currents from the surface and bulk layer of InN. The effective spin-orbit coupling coefficient (SOC) in the surface electron layer is suggested to be of opposite sign to that in the bulk. The results constitute a comprehensive understanding of the role of surface electron layer in spin transport in InN. This work reveals an approach to explore spin-orbit coupling in systems like InN.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.Dc Spin polarized transport in semiconductors
73.50.Pz Photoconduction and photovoltaic effects
73.61.Le Other inorganic semiconductors
79.60.Dp Adsorbed layers and thin films

Tunable magnetic states in hexagonal boron nitride sheets

Eduardo Machado-Charry, Paul Boulanger, Luigi Genovese, Normand Mousseau, and Pascal Pochet

Appl. Phys. Lett. 101, 132405 (2012); http://dx.doi.org/10.1063/1.4754143 (4 pages) | Cited 5 times

Online Publication Date: 24 September 2012

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Magnetism in two dimensional atomic sheets has attracted considerable interest as its existence could allow the development of electronic and spintronic devices. The existence of magnetism is not sufficient for devices, however, as states must be addressable and modifiable through the application of an external drive. We show that defects in hexagonal boron nitride present a strong interplay between the N-N distance in the edge and the magnetic moments of the defects. By stress-induced geometry modifications, we change the ground state magnetic moment of the defects. This control is made possible by the triangular shape of the defects as well as the strong spin localisation in the magnetic state.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Pp Magnetic semiconductors
71.55.Eq III-V semiconductors

Magnetostriction of TbFe2-based alloy treated in a semi-solid state with a high magnetic field

Qiang Wang, Yin Liu, Tie Liu, Pengfei Gao, Kai Wang, and Jicheng He

Appl. Phys. Lett. 101, 132406 (2012); http://dx.doi.org/10.1063/1.4754595 (3 pages)

Online Publication Date: 25 September 2012

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We investigated the effect of a high magnetic field on the magnetostriction of TbFe2-based alloy during a semi-solid state process. With the application of a high magnetic field, magnetostrictions under free and compressive prestress conditions remarkably increased. Obvious magnetically anisotropic behavior of the TbFe2-based alloy was observed. A high 〈111〉 orientation of TbFe2 phase along the magnetic-field direction was produced. The increase in magnetostriction and the magnetically anisotropic behavior were attributed to the 〈111〉 orientation of TbFe2 phase during the treatment in the semi-solid state induced by the magnetic field.
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75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys

Edge atoms effects on the perpendicular anisotropy of ultrathin magnetic layers

J. Geshev, A. Gündel, I. Zaharieva, and J. E. Schmidt

Appl. Phys. Lett. 101, 132407 (2012); http://dx.doi.org/10.1063/1.4754621 (4 pages)

Online Publication Date: 25 September 2012

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The present work reports experimental and theoretical results for electrodeposited Co/Au(111) ultrathin layers with very specific magnetic behavior. We show that the observed two peaks in the out-of-plane magnetization versus deposition time variation could be explained by the remarkably high perpendicular anisotropy of the perimeter atoms of low-dimensional islands formed during the layer-by-layer growth, as compared to that of the surface atoms. Our results indicate that it is possible to sustain high anisotropy in very small grains without coming across the superparamagnetic limit, opening excellent opportunities for materials engineering.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Pq Electrodeposition, electroplating
75.75.Cd Fabrication of magnetic nanostructures
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Evidences for direct magnetic patterning via diffusive transformations using femtosecond laser interferometry

N. I. Polushkin, V. Oliveira, O. Conde, R. Vilar, Yu. N. Drozdov, A. Apolinário, A. García-García, J. M. Teixeira, and G. N. Kakazei

Appl. Phys. Lett. 101, 132408 (2012); http://dx.doi.org/10.1063/1.4754623 (5 pages)

Online Publication Date: 25 September 2012

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The application of femtosecond laser interferometry to direct patterning of thin-film magnetic alloys is demonstrated. The formation of stripe gratings with submicron periodicities is achieved in Fe1−xVx (x = 18–34 wt. %) layers, with a difference in magnetic moments up to Δμ/μ ∼ 20 between adjacent stripes but without any significant development of the topographical relief (<1% of the film thickness). The produced gratings exhibit a robust effect of their anisotropy shape on magnetization curves in the film plane. The obtained data witness ultrafast diffusive transformations associated with the process of spinodal decomposition and demonstrate an opportunity for producing magnetic nanostructures with engineered properties upon this basis.
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75.70.Ak Magnetic properties of monolayers and thin films
81.16.-c Methods of micro- and nanofabrication and processing
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
78.47.J- Ultrafast spectroscopy (<1 psec)
66.30.-h Diffusion in solids
75.30.Gw Magnetic anisotropy

Microstructural and ferromagnetic resonance properties of epitaxial nickel ferrite films grown by chemical vapor deposition

N. Li, S. Schäfer, R. Datta, T. Mewes, T. M. Klein, and A. Gupta

Appl. Phys. Lett. 101, 132409 (2012); http://dx.doi.org/10.1063/1.4754847 (4 pages)

Online Publication Date: 25 September 2012

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Microstructural and ferromagnetic resonance properties of epitaxial nickel ferrite (NiFe2O4) films grown by direct liquid injection chemical vapor deposition are reported. While high-quality epitaxial growth of NiFe2O4 films on (100)-oriented MgAl2O4 substrate is confirmed by high resolution transmission electron microscopy, bright field (diffraction contrast) TEM studies reveal the presence of dislocations and also dark diffused contrast areas, which originate from antiphase domains. Angle and frequency-dependent ferromagnetic resonance (FMR) experiments are conducted to determine the magnetic anisotropy and the magnetic relaxation. A low out-of-plane FMR linewidth of ∼160 Oe has been observed at a frequency of 10 GHz.
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75.70.Ak Magnetic properties of monolayers and thin films
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
75.30.Gw Magnetic anisotropy
75.50.Gg Ferrimagnetics

Magnetic and electronic properties of D022-Mn3Ge (001) films

H. Kurt, N. Baadji, K. Rode, M. Venkatesan, P. Stamenov, S. Sanvito, and J. M. D. Coey

Appl. Phys. Lett. 101, 132410 (2012); http://dx.doi.org/10.1063/1.4754123 (3 pages) | Cited 1 time

Online Publication Date: 25 September 2012

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Oriented thin films of Mn3Ge with the tetragonal D022 structure, grown on strontium titanate substrates, exhibit a low magnetization Ms = 73 kA m−1 combined with high uniaxial anisotropy Ku = 0.91 MJ m−3 at 300 K, making them potentially useful for thermally stable sub-10 nm spin torque memory elements. The highly ordered epitaxial Mn3Ge (001) films show 46% diffusive spin polarization at the Fermi level, measured by point contact Andreev reflection. Density functional calculations show that the compounds are ferrimagnetic, with anisotropic spin polarization at the Fermi level.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
75.30.Gw Magnetic anisotropy

Critical effect of spin-dependent transport in a tunnel barrier on enhanced Hanle-type signals observed in three-terminal geometry

Tetsuya Uemura, Kenji Kondo, Jun Fujisawa, Ken-ichi Matsuda, and Masafumi Yamamoto

Appl. Phys. Lett. 101, 132411 (2012); http://dx.doi.org/10.1063/1.4754545 (4 pages) | Cited 1 time

Online Publication Date: 26 September 2012

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The MgO thickness dependence of Hanle signals in Co50Fe50/MgO/n-Si tunnel junctions was investigated using a three-terminal geometry. The observed Hanle signal is several orders of magnitude stronger than the predicted value by conventional theory as reported in many literatures. Furthermore, the magnitude of the spin signal depends on the junction resistance rather than the channel resistance, implying that the largest part of the observed Hanle signal is not caused by spin accumulation in the semiconductor region. A possible origin of the observed strong Hanle signal is due to a modulation of the tunneling resistance by a magnetic field, which is induced by the spin precession in localized states formed in the vicinity of the Co50Fe50/MgO interface.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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