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18 Aug 2008

Volume 93, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 073101 (2008); http://dx.doi.org/10.1063/1.2970055 (3 pages)

A. J. Du, Y. Chen, G. Q. Lu, and Sean C. Smith
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Selective disordering of InAs/InGaAs dots-in-a-well structure patterned with sol-gel derived SiO2 strips imprinted by soft mold technique

C. K. Chia, M. Suryana, W. Zhao, H. Y. Low, and M. Hopkinson

Appl. Phys. Lett. 93, 071907 (2008); http://dx.doi.org/10.1063/1.2973164 (3 pages) | Cited 1 time

Online Publication Date: 22 August 2008

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Selective impurity free vacancy disordering of InAs/InGaAs quantum dot (QD) structures imprinted with sol-gel derived SiO2 strips via a polyethylene terepthalate soft mold has been investigated. Wavelength blueshift of up to 220 nm for areas capped with the sol-gel derived SiO2 is demonstrated. The imprinted SiO2 strips were used as hard mask for plasma etching of GaAs ridge waveguide structures and were found to have similar hardness as the SiO2 prepared by plasma-enhanced chemical vapor deposition. QD intermixing using sol-gel derived SiO2 with step-thickness profile was demonstrated, and a one-step SiO2 imprinting technique for multiple band gap QD intermixing is proposed.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
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)
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Blue and red electroluminescence of Europium-implanted metal-oxide-semiconductor structures as a probe for the dynamics of microstructure

L. Rebohle, J. Lehmann, S. Prucnal, A. Kanjilal, A. Nazarov, I. Tyagulskii, W. Skorupa, and M. Helm

Appl. Phys. Lett. 93, 071908 (2008); http://dx.doi.org/10.1063/1.2964176 (3 pages) | Cited 13 times

Online Publication Date: 22 August 2008

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The strong blue and red electroluminescence from Eu-implanted SiO2 layers were investigated as a function of implantation and annealing conditions. It is shown that the red electroluminescence assigned to Eu3+ ions is favored by low Eu concentrations, low annealing temperatures, and short annealing times. Based on a more quantitative analysis of the electroluminescence spectra this preference is explained by a shorter supply of oxygen for higher Eu concentrations and the growth of Europium or Europium oxide clusters with increasing annealing temperatures and annealing times. The correlation between electroluminescence and microstructure is supported by transmission electron microscopy investigations and demonstrates that the electroluminescence of Eu-implanted SiO2 layers can serve as a probe for the microstructural development in the active layer of the light emitter.
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78.60.Fi Electroluminescence
68.37.Og High-resolution transmission electron microscopy (HRTEM)
61.72.Cc Kinetics of defect formation and annealing

Complete thin film mechanical characterization using picosecond ultrasonics and nanostructured transducers: experimental demonstration on SiO2

P. A. Mante, J. F. Robillard, and A. Devos

Appl. Phys. Lett. 93, 071909 (2008); http://dx.doi.org/10.1063/1.2975171 (3 pages) | Cited 7 times

Online Publication Date: 22 August 2008

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Complete mechanical measurements are performed in submicron films using the picosecond ultrasonic technique. The Al layer deposited on the top of the sample acting as a transducer is replaced with a nanostructured Al film. Using an usual picosecond ultrasonic setup we can excite and detect high-frequency longitudinal and surface acoustic waves. From this we can deduce Young’s modulus and Poisson’s ratio of any isotropic thin film. Experimental results obtained for a thin silica layer on silicon are in very good agreement with literature.
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68.60.Bs Mechanical and acoustical properties
62.20.dj Poisson's ratio
81.40.Jj Elasticity and anelasticity, stress-strain relations

Negative refraction at the pure Ag/air interface observed in the visible Drude region

Yun-Hua Wu, Wen Gu, Yue-Rui Chen, Zhong-Hong Dai, Wei-Xi Zhou, Yu-Xiang Zheng, and Liang-Yao Chen

Appl. Phys. Lett. 93, 071910 (2008); http://dx.doi.org/10.1063/1.2975155 (3 pages) | Cited 1 time

Online Publication Date: 22 August 2008

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Pure negative refraction was found for a series of prismlike Ag film samples measured in the visible Drude region. Results show that the pseudonegative refraction index nm changes with the photon energy and has a spectral trend to be less negative with the increasing energy. Light refraction will be expected to be positive in the higher energy region where the interband transitions dominate the interaction between the electrons and photons in Ag.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Bz Metals and metallic alloys
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Ultrathin SiO2 layer on atomically flat Si(111) surfaces with excellent electrical characteristics formed by nitric acid oxidation method

Woo-Byoung Kim, Asuha, Taketoshi Matsumoto, and Hikaru Kobayashi

Appl. Phys. Lett. 93, 072101 (2008); http://dx.doi.org/10.1063/1.2970040 (3 pages) | Cited 6 times

Online Publication Date: 18 August 2008

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We have developed a method of formation of atomically smooth Si/SiO2 interfaces by oxidation of atomically flat Si(111) surfaces by use of azeotropic nitric acid (HNO3) aqueous solutions (i.e., 68 wt % HNO3 at 121 °C). For the SiO2 layer on the atomically smooth Si substrates, the concentration of suboxide species, Si2+, is ∼ 50% of that on the rough Si substrates, and the valence band discontinuity is higher by ∼ 0.1 eV. In this case, the leakage current flowing through the ∼ 1.2 nm SiO2 is low, and further decreased by postmetallization annealing at 250 °C in hydrogen (e.g., 0.5 A/cm2 at VG = 1 V).
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing

Broadband electrically detected magnetic resonance of phosphorus donors in a silicon field-effect transistor

L. H. Willems van Beveren, H. Huebl, D. R. McCamey, T. Duty, A. J. Ferguson, R. G. Clark, and M. S. Brandt

Appl. Phys. Lett. 93, 072102 (2008); http://dx.doi.org/10.1063/1.2960356 (3 pages) | Cited 13 times

Online Publication Date: 19 August 2008

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We report electrically detected magnetic resonance of phosphorus donors in a silicon field-effect transistor. An on-chip transmission line is used to generate the oscillating magnetic field allowing broadband operation. At millikelvin temperatures, continuous wave spectra were obtained up to 40 GHz, using both magnetic field and microwave frequency modulation. The spectra reveal the hyperfine-split electron spin resonances characteristic for Si:P and a central feature which displays the fingerprint of spin-spin scattering in the two-dimensional electron gas.
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76.30.Lh Other ions and impurities
85.75.Hh Spin polarized field effect transistors

Low Schottky barrier height for silicides on n-type Si (100) by interfacial selenium segregation during silicidation

Hoong-Shing Wong, Lap Chan, Ganesh Samudra, and Yee-Chia Yeo

Appl. Phys. Lett. 93, 072103 (2008); http://dx.doi.org/10.1063/1.2970958 (3 pages) | Cited 13 times

Online Publication Date: 20 August 2008

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The electron Schottky barrier height ΦBn modulation for NiSi and PtSi formed on selenium-implanted n-type Si (100) has been experimentally investigated. Selenium (Se) segregation is observed at the silicide/n-Si(100) interface during silicidation process. ΦBn of 83 and 120 meV were achieved for Se segregated NiSi and PtSi on n-Si (100) interfaces, respectively. Contrary to previously reported Fermi level depinning effect in monolayer Se-passivated n-Si (100), the low ΦBn achieved in this work points to metal silicide Fermi level pinning near to conduction band EC of n-Si (100).
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73.30.+y Surface double layers, Schottky barriers, and work functions
71.20.Mq Elemental semiconductors

Influence of top surface passivation on bottom-channel hole mobility of ultrathin SiGe- and Ge-on-insulator

Haigui Yang, Dong Wang, Hiroshi Nakashima, Hongye Gao, Kana Hirayama, Ken-ichi Ikeda, Satoshi Hata, and Hideharu Nakashima

Appl. Phys. Lett. 93, 072104 (2008); http://dx.doi.org/10.1063/1.2972114 (3 pages) | Cited 9 times

Online Publication Date: 20 August 2008

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Bottom-channel hole mobility was examined by a pseudo-metal-oxide-semiconductor field-effect transistors method for ultrathin SiGe-on-insulator (SGOI) and Ge-on-insulator (GOI), which were fabricated using Ge condensation by dry oxidation. By comparing samples with and without a top SiO2 layer, we investigated the influence of top surface passivation on bottom-channel hole mobility. Mobility degradation was found in an ultrathin SGOI/GOI layer without top SiO2 and became more serious with a decrease in the thickness of the SGOI/GOI layer, which strongly suggested that top surface passivation is necessary to evaluate accurate channel mobility. A 13-nm-thick GOI with passivation showed a high mobility value of 440 cm2/V s.
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85.30.Tv Field effect devices

1,8-octanedithiol as a processing additive for bulk heterojunction materials: Enhanced photoconductive response

Nelson E. Coates, In-Wook Hwang, Jeffrey Peet, Guillermo C. Bazan, Daniel Moses, and Alan J. Heeger

Appl. Phys. Lett. 93, 072105 (2008); http://dx.doi.org/10.1063/1.2969405 (3 pages) | Cited 15 times

Online Publication Date: 20 August 2008

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We present measurements of steady state and transient (τ<70 ps) photoconductivity of the low bandgap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] mixed with [6,6]-phenyl C71-butyric acid methyl ester films processed with and without the 1,8-octanedithiol additive. The data demonstrate enhanced photoconductive response in the bulk heterojunction material processed with the additive. The increase results primarily from enhanced carrier mobility and to a lesser extent from a more efficient photogeneration of mobile carriers and longer mobile carrier lifetimes. The enhanced photoresponse is consistent with the increase in power conversion efficiency obtained from solar cells in which the bulk heterojunction film is processed using 1,8-octanedithiol.
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73.50.Pz Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance
72.80.Le Polymers; organic compounds (including organic semiconductors)
73.61.Ph Polymers; organic compounds

Anisotropic hole-mass tensor of CuIn1−xGax(S,Se)2: Presence of free carriers narrows the energy gap

Clas Persson

Appl. Phys. Lett. 93, 072106 (2008); http://dx.doi.org/10.1063/1.2969467 (3 pages) | Cited 11 times

Online Publication Date: 20 August 2008

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Analysis of the band edges of CuIn1−xGax(S,Se)2 with x = 0.0, 0.5, and 1.0 reveals that (i) CuIn1−xGaxS2 has larger effective electron mc and hole mv masses than CuIn1−xGaxSe2; (ii) whereas Ga content affects band curvatures only slightly, the sign of the crystal-field split Δcf as well as the spin-orbit coupling affect mv strongly; (iii) the optical response ε2(ℏω) is comparable for all six compounds; and (iv) band filling of electrons (n = 1019 cm−3) and holes (p = n) narrows the band gap by Eg ≈ Eg0−0.1 eV and generates an optical band gap of Egopt ≈ Eg+0.2 eV.
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71.20.Nr Semiconductor compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.70.Ch Crystal and ligand fields
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Effect of carbon codoping on boron diffusion in amorphous silicon

L. A. Edelman, S. Jin, K. S. Jones, R. G. Elliman, and L. M. Rubin

Appl. Phys. Lett. 93, 072107 (2008); http://dx.doi.org/10.1063/1.2975833 (3 pages) | Cited 2 times

Online Publication Date: 22 August 2008

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The effect of carbon codoping on boron diffusion in amorphous silicon is investigated during low temperature annealing. The diffusivity of boron is unaffected by carbon codoping, but the fraction of mobile boron is observed to increase with increasing carbon concentration. A concomitant reduction in boron clustering is also observed at higher carbon coimplant concentrations, consistent with a change in the local trap concentration. This is consistent with carbon possibly acting as a trap site for boron and thereby changing the size and dynamics of the boron cluster formation.
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68.35.Fx Diffusion; interface formation
61.72.uf Ge and Si

Relaxation of strained silicon on Si0.5Ge0.5 virtual substrates

J. Parsons, R. J. H. Morris, D. R. Leadley, E. H. C. Parker, D. J. F. Fulgoni, and L. J. Nash

Appl. Phys. Lett. 93, 072108 (2008); http://dx.doi.org/10.1063/1.2975188 (3 pages) | Cited 5 times

Online Publication Date: 22 August 2008

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Strain relaxation has been studied in tensile strained silicon layers grown on Si0.5Ge0.5 virtual substrates, for layers many times the critical thickness, using high resolution x-ray diffraction. Layers up to 30 nm thick were found to relax less than 2% by the glide of preexisting 60° dislocations. Relaxation is limited because many of these dislocations dissociate into extended stacking faults that impede the dislocation glide. For thicker layers, nucleated microtwins were observed, which significantly increased relaxation to 14%. All these tensile strained layers are found to be much more stable than layers with comparable compressive strain.
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81.05.Cy Elemental semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Mm Grain and twin boundaries
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Room temperature hydrogen detection using Pd-coated GaN nanowires

Wantae Lim, J. S. Wright, B. P. Gila, Jason L. Johnson, Ant Ural, Travis Anderson, F. Ren, and S. J. Pearton

Appl. Phys. Lett. 93, 072109 (2008); http://dx.doi.org/10.1063/1.2975173 (3 pages) | Cited 28 times

Online Publication Date: 22 August 2008

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Multiple GaN nanowires produced by thermal chemical vapor deposition were employed as gas sensors for detection of hydrogen at concentrations from 200–1500 ppm in N2 at 300 K. Palladium coating of the wires improved the sensitivity by a factor of up to 11 at low ppm concentrations relative to uncoated controls. The GaN nanowires showed relative responses of ∼ 7.4% at 200 ppm and ∼ 9.1% at 1500 ppm H2 in N2 after a 10 min exposure. Upon removal of hydrogen from the measurement ambient, ∼ 90% of the initial GaN conductance was recovered within 2 min. Temperature dependent measurements showed a larger relative response and shorter response time at elevated temperature. The adsorption activation energy of the sensor was 2.2 kcal mol−1 at 3000 ppm H2 in N2. These sensors exhibit low power consumption (<0.6 mW) at 300 K.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.35.-p Nanoelectronic devices

Valence band offset of MgO/4H-SiC heterojunction measured by x-ray photoelectron spectroscopy

B. L. Zhang, F. F. Cai, G. S. Sun, H. B. Fan, P. F. Zhang, H. Y. Wei, X. L. Liu, S. Y. Yang, Q. S. Zhu, and Z. G. Wang

Appl. Phys. Lett. 93, 072110 (2008); http://dx.doi.org/10.1063/1.2975168 (3 pages) | Cited 6 times

Online Publication Date: 22 August 2008

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The valence band offset (VBO) of MgO(111)/4H-SiC heterojunction has been directly measured by x-ray photoelectron spectroscopy. The VBO is determined to be 3.65±0.23 eV and the conduction band offset is deduced to be 0.92±0.23 eV, indicating that the heterojunction has a type-I band alignment. The accurate determination of the valence and conduction band offsets is important for the applications of MgO/SiC optoelectronic devices.
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73.20.At Surface states, band structure, electron density of states
79.60.-i Photoemission and photoelectron spectra

Zn- and O-face polarity effects at ZnO surfaces and metal interfaces

Yufeng Dong, Z-Q. Fang, D. C. Look, G. Cantwell, J. Zhang, J. J. Song, and L. J. Brillson

Appl. Phys. Lett. 93, 072111 (2008); http://dx.doi.org/10.1063/1.2974983 (3 pages) | Cited 21 times

Online Publication Date: 22 August 2008

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Depth-resolved cathodoluminescence spectroscopy, current-voltage, capacitance-voltage, and deep level transient spectroscopy of ZnO (0001) Zn- and (000math) O-polar surfaces and metal interfaces show systematically higher Zn-face near band edge emission and lower near-surface defect emission. Even with remote plasma decreases of the 2.5 eV near-surface defect emission, (0001)-Zn face emission quality still exceeds that of (000math)-O face. Ultrahigh vacuum-deposited Au and Pd diodes on as-received and O2/He plasma-cleaned surfaces display a strong polarity dependence that correlates with defect emissions, traps, and interface chemistry. A comprehensive model accounts for the polarity-dependent transport properties and their correlations with carrier concentration profiles.
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71.55.Gs II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Capacitance characteristics of phase separated La0.5Ca0.5MnO3/Nb–SrTiO3 p-n junction

B. T. Xie, Y. G. Zhao, and C. M. Xiong

Appl. Phys. Lett. 93, 072112 (2008); http://dx.doi.org/10.1063/1.2973904 (3 pages) | Cited 6 times

Online Publication Date: 22 August 2008

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The capacitance characteristics of La0.5Ca0.5MnO3/Nb–SrTiO3 p-n junction and magnetic property have been investigated. The magnetic field-induced increase in ferromagnetic metallic phase, irreversibility, and the exchange bias effect were observed. The junction also shows a remarkable thermal hysteresis of capacitance, a giant positive magnetocapacitance (MC), a remarkable difference of MC for the zero field cooling and field cooling processes, and a memory effect of magnetic field. The results can be understood in terms of phase separation. This work demonstrates the remarkable tunability of the capacitance for phase separated manganite heterojunctions, which may have potential applications.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
64.75.-g Phase equilibria
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Carbon nanotube Josephson junctions with Nb contacts

E. Pallecchi, M. Gaaß, D. A. Ryndyk, and Ch. Strunk

Appl. Phys. Lett. 93, 072501 (2008); http://dx.doi.org/10.1063/1.2971034 (3 pages) | Cited 11 times

Online Publication Date: 18 August 2008

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We report on the preparation of carbon nanotube Josephson junctions using superconducting electrodes made of niobium. Gate-controllable supercurrents with values of up to 30 nA are induced by the proximity effect. The IV curves are hysteretic at low temperature and the corresponding switching histograms have a width of 0.5%–2%. An on-chip resistive environment integrated in the sample layout is used to increase the switching current.
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74.50.+r Tunneling phenomena; Josephson effects
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

Enhancement of optical and magneto-optical effects in three-dimensional opal/Fe3O4 magnetic photonic crystals

V. V. Pavlov, P. A. Usachev, R. V. Pisarev, D. A. Kurdyukov, S. F. Kaplan, A. V. Kimel, A. Kirilyuk, and Th. Rasing

Appl. Phys. Lett. 93, 072502 (2008); http://dx.doi.org/10.1063/1.2973150 (3 pages) | Cited 7 times

Online Publication Date: 18 August 2008

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Three-dimensional magnetic photonic crystals, based on an artificial opal matrix with embedded magnetite Fe3O4, were investigated in both transmission and reflection in the near-infrared and visible spectral range. A strong enhancement of the polar Kerr effect and a modification of the Faraday effect have been found near the photonic band gap at about 1.8 eV. Surprisingly the shapes of the loops of magnetic hysteresis measured by magnetic circular dichroism were found to depend on the wavelength of light. This observation has been explained using a model where two types of magnetite particles have different coercive fields.
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42.70.Qs Photonic bandgap materials
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials

Antiferromagnetic iridium manganese based intermediate layers for perpendicular magnetic recording media

Kumar Srinivasan, S. N. Piramanayagam, and Rachid Sbiaa

Appl. Phys. Lett. 93, 072503 (2008); http://dx.doi.org/10.1063/1.2970032 (3 pages) | Cited 5 times

Online Publication Date: 18 August 2008

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Current generation CoCrPt oxide based perpendicular magnetic recording media use two Ru-based intermediate layers in order to grow crystallographically textured, and magnetically isolated granular media. In this work, the advantage of replacing the Ru grain isolation layer with antiferromagnetic IrMn is demonstrated. Media samples using 7.5 nm thick IrMn intermediate layers show perpendicular texture with dispersion below 4°, coercivity of over 4000 Oe alongside magnetic exchange decoupling, average grain sizes of 6 nm with distributions under 14%, and thermal stability factor of 88. The IrMn layer may also help to stabilize the recording layer grains against thermal instability effects.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ss Magnetic recording materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions

Exchange coupling assisted FePtC perpendicular recording media

J. F. Hu, J. S. Chen, Y. F. Ding, B. C. Lim, W. L. Phyoe, and B. Liu

Appl. Phys. Lett. 93, 072504 (2008); http://dx.doi.org/10.1063/1.2974794 (3 pages) | Cited 13 times

Online Publication Date: 19 August 2008

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Exchange coupling assisted perpendicular recording media consisting of a 10 nm magnetically hard FePtC layer with a FePtC soft overlayer of a different thickness were investigated. Both the coercivity and the saturation field of the FePtC film decreased after introducing a magnetically soft FePtC overlayer. The soft FePt grains were located on top of the underlying FePt grains and at the grain boundaries. Some of the hard and soft grains were separated by a C layer accumulated on the hard magnetic FePtC layer surface. The strength of the exchange coupling between soft and hard grains depended on the C layer thickness.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries

Steplike versus continuous domain propagation in Co/Pd multilayer films

C. M. Günther, F. Radu, A. Menzel, S. Eisebitt, W. F. Schlotter, R. Rick, J. Lüning, and O. Hellwig

Appl. Phys. Lett. 93, 072505 (2008); http://dx.doi.org/10.1063/1.2968305 (3 pages) | Cited 8 times

Online Publication Date: 19 August 2008

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We investigate the microscopic reversal behavior in perpendicular-anisotropy magnetic thin films using an integrated mask-sample design that allows probing a nanoscale sample region with soft x-rays. Local hysteresis loops and spectroholography images are obtained from the transmitted signal exploiting x-ray magnetic circular dichroism. Our data provide direct evidence of microscopic spin-flip avalanches, such as responsible for Barkhausen noise. In comparison with macroscopic magnetometry measurements we find evidence for the sputter pressure dependent introduction of local defects that prevent a continuous domain wall motion but are not strong enough to introduce the appearance of microscopic return point memory.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects

Tunable magnetic order of Co nanoparticles and magnetotransport in Co/ZnO nanocomposites

C. Y. Hsu, J. C. A. Huang, S. F. Chen, C. P. Liu, S. J. Sun, and Yonhua Tzeng

Appl. Phys. Lett. 93, 072506 (2008); http://dx.doi.org/10.1063/1.2959081 (3 pages) | Cited 3 times

Online Publication Date: 20 August 2008

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We demonstrate tunable magnetic order of cobalt nanoparticles in Co/ZnO nanocomposites. High-density electronic states in ZnO formed during high vacuum annealing help generate bound and free charge carriers, which in turn enable the stable magnetic ordering of Co nanoparticles in the Co/ZnO nanocomposites in a tunable manner. This is demonstrated by the following experimental observations: (i) enhanced spontaneous magnetization and coercivity, (ii) transition from semiconducting to metallic electrical-transport, and (iii) transverse magnetotransport transition from negative magnetoresistance to the anomalous Hall effect. The work explores a route to manipulate the magnetic order of magnetic nanoparticles by means of intentionally generated defects in oxides.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
73.43.Qt Magnetoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.60.+g Mixed conductivity and conductivity transitions

Atomically smooth and single crystalline MnTiO3 thin films with a ferrotoroidic structure

H. Toyosaki, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 93, 072507 (2008); http://dx.doi.org/10.1063/1.2975373 (3 pages) | Cited 1 time

Online Publication Date: 22 August 2008

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We report the epitaxial growth and magnetic properties of MnTiO3 thin films with an ilmenite structure. Although the lattice mismatch with sapphire substrates was as large as 8.0%, highly crystalline films with atomically flat surfaces were grown by using pulsed laser deposition. X-ray diffraction and transmission electron microscopy showed that the optimized film had almost a single crystalline structure with totally relaxed lattice parameters, inducing periodic misfit dislocations at the film/substrate interface. The magnetization curve showed an abrupt increase due to spin flopping when the magnetic field along the c-axis exceeded the critical magnetic field (μ0Hc ∼ 6 T). Due to the spin flopping, we concluded that MnTiO3 had a ferrotoroidic structure and, thus, was magnetoelectrically active.
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68.55.at Other materials
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.50.Dd Nonmetallic ferromagnetic materials
81.16.Mk Laser-assisted deposition
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics
75.80.+q Magnetomechanical effects, magnetostriction

Direct observation and control of the Walker breakdown process during a field driven domain wall motion

S. Glathe, R. Mattheis, and D. V. Berkov

Appl. Phys. Lett. 93, 072508 (2008); http://dx.doi.org/10.1063/1.2975181 (3 pages) | Cited 17 times

Online Publication Date: 22 August 2008

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We report the real-time study of a domain wall motion in giant magnetoresistance nanostrips. We have visualized the Walker breakdown process (WBP) [ N. L. Schryer and L. R. Walker, J. Appl. Phys. 45, 5406 (1974) ] in single shot experiments. The domain wall motion above the Walker breakdown is highly nonperiodic. Surprisingly, the time intervals of movement are equal or larger than those where the domain wall nearly stops. When an additional transversal magnetic field is applied, domain wall motion becomes more regular, enabling the study of the WBP in more detail. A sufficiently large transverse field can suppress the WBP completely.
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75.60.Ch Domain walls and domain structure
75.47.De Giant magnetoresistance

Coplanar waveguide radio frequency ferromagnetic parametric amplifier

Mingqiang Bao, Alexander Khitun, Yina Wu, Joo-Young Lee, Kang L. Wang, and Ajey P. Jacob

Appl. Phys. Lett. 93, 072509 (2008); http://dx.doi.org/10.1063/1.2975174 (2 pages) | Cited 11 times

Online Publication Date: 22 August 2008

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In this letter, we report a coplanar waveguide ferromagnetic parametric amplifier fabricated on a ferromagnetic Permalloy thin film. It shows a power gain of 4 dB at 1.15 GHz when the pump power is 11.1 dBm at the pump frequency of 2.30 GHz under the bias field of 13 Oe. This prototype ferromagnetic device can be integrated with the complementary metal-oxide semiconductor process technology and has potential applications as a spin-wave amplifier, a low noise amplifier, or an active bandpass filter.
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84.40.Az Waveguides, transmission lines, striplines
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
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