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2 Nov 2009

Volume 95, Issue 18, Articles (18xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 183504 (2009); http://dx.doi.org/10.1063/1.3256223 (3 pages)

Hoon-Sik Kim, Sang Min Won, Young-Geun Ha, Jong-Hyun Ahn, Antonio Facchetti, Tobin J. Marks, and John A. Rogers
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Enhanced thermal stability of Pt electrodes for flat epitaxial biferroic-YMnO3/Pt heterostructures

R. Bachelet, R. Muralidharan, F. Rigato, N. Dix, X. Martí, J. Santiso, F. Sánchez, and J. Fontcuberta

Appl. Phys. Lett. 95, 181907 (2009); http://dx.doi.org/10.1063/1.3259417 (3 pages) | Cited 1 time

Online Publication Date: 5 November 2009

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We have investigated the thermal stability of platinum electrodes on oxide substrates for oxide-based devices. We show that flat epitaxial Pt(111) bottom electrodes, deposited on SrTiO3(111) and Al2O3(0001) substrates, can be stable against dewetting up to usual oxide-deposition temperatures (Ts) by increasing Pt film thickness (tPt) and preferably using SrTiO3(111) rather than Al2O3(0001) substrates. Subsequently, high-quality epitaxial biferroic YMnO3/Pt/oxide-substrate heterostructures have been grown. A diagram of morphological and crystalline quality versus tPt and Ts is given for both YMnO3/Pt/SrTiO3(111) and YMnO3/Pt/Al2O3(0001) heterostructures. These results shall guideline the growth of other functional oxide thin films on Pt electrodes.
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68.60.Dv Thermal stability; thermal effects
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.55.-a Thin film structure and morphology

Thermal properties of char obtained by pyrolysis: A molecular dynamics simulation study

Maxim A. Makeev and Deepak Srivastava

Appl. Phys. Lett. 95, 181908 (2009); http://dx.doi.org/10.1063/1.3249632 (3 pages) | Cited 3 times

Online Publication Date: 5 November 2009

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The thermal conductivity of pyrolytic char obtained by ultrahigh temperature decomposition of polyethylene specimen via molecular dynamics simulations is investigated as a function of temperature and microstructural characteristics. We find that the simulated thermal conductivity dependence on the average coordination number is modified by formation of graphene-like microtopological features in carbonaceous char. The dependence of thermal conductivity on temperature and average coordination number is explained in terms of an analytical model, based on the Einstein’s theory of heat transport. The deviations due to the formation of graphene sheet-like units are taken into consideration by introducing corresponding corrections in the elastic properties of char.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations

Direct integration of active Ge1−x(Si4Sn)x semiconductors on Si(100)

Junqi Xie, J. Tolle, V. R. D’Costa, A. V. G. Chizmeshya, J. Menéndez, and J. Kouvetakis

Appl. Phys. Lett. 95, 181909 (2009); http://dx.doi.org/10.1063/1.3242002 (3 pages) | Cited 6 times

Online Publication Date: 5 November 2009

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Doped and intrinsic Ge1−x−ySixSny alloys are synthesized directly on Si(100) using simple deposition chemistries and their optical and electrical properties are determined. Tuning the Si/Sn ratio at ∼ 4 yields strain-free films with Ge-like cell dimensions, while variation of the ratio around this value produces compressively strained, tetragonal structures with an in-plane lattice constant “pinned” to a value close to that of pure Ge (5.658 Å). First-principles calculations show that mixing entropy thermodynamically stabilizes SiGeSn in contrast to GeSn analogs with the same Sn content. GeSn and SiGeSn are predicted to become metastable for 2% and 12% Sn, respectively, in good agreement with experiment.
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73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Quantum confined Stark effect and corresponding lifetime reduction in a single InxGa1−xN quantum disk

Mark J. Holmes, Young S. Park, Jamie H. Warner, and Robert A. Taylor

Appl. Phys. Lett. 95, 181910 (2009); http://dx.doi.org/10.1063/1.3257698 (3 pages) | Cited 2 times

Online Publication Date: 5 November 2009

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Time-integrated and time-resolved microphotoluminescence studies were carried out on InxGa1−xN quantum disks embedded in GaN nanocolumns grown by molecular beam epitaxy. Emission at ∼ 3.33 eV from confined states was detected and observed to blueshift with excitation power; a result of charge screening and the quantum confined Stark effect. Due to the reduced band bending and resulting increased overlap of the confined electron and hole wave functions, the lifetime of the emission was measured to decrease with increasing excitation power. The saturation of the blueshift and lifetime reduction follows that of the peak intensity, indicating a Stark screening process.
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78.67.De Quantum wells
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Jq Electro-optical effects

Measurement of heat capacity and enthalpy of formation of nickel silicide using nanocalorimetry

Ravi K. Kummamuru, Lito De La Rama, Liang Hu, Mark D. Vaudin, Mikhail Y. Efremov, Martin L. Green, David A. LaVan, and Leslie H. Allen

Appl. Phys. Lett. 95, 181911 (2009); http://dx.doi.org/10.1063/1.3255009 (3 pages) | Cited 10 times

Online Publication Date: 5 November 2009

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The total enthalpy of reaction and heat capacity to 850 °C were measured using differential scanning nanocalorimetry (nano-DSC) for the reaction of a nickel and silicon bilayer at heating rates up to 106 K/s. Exothermic dips in heat capacity attributed to nickel silicide formation were found along with indications of phase changes at 430 and 550 °C. The postreaction phases were identified using electron backscattered diffraction. Samples with a Ni:Si molar ratio of 1.2 heated to 850 °C were a mixture of orthorhombic NiSi and the θ-phase (hexagonal—Ni2Si); samples heated to 790 °C resulted in predominantly NiSi.
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82.60.Fa Heat capacities and heats of phase transitions
82.60.Cx Enthalpies of combustion, reaction, and formation
65.40.Ba Heat capacity
07.20.Fw Calorimeters
79.20.Hx Electron impact: secondary emission
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Mechanics of hemispherical electronics

Shuodao Wang, Jianliang Xiao, Inhwa Jung, Jizhou Song, Heung Cho Ko, Mark P. Stoykovich, Yonggang Huang, Keh-Chih Hwang, and John A. Rogers

Appl. Phys. Lett. 95, 181912 (2009); http://dx.doi.org/10.1063/1.3256185 (3 pages) | Cited 4 times

Online Publication Date: 5 November 2009

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A simple analytical model is established for the development of hemisphere electronics, which has many important applications in electronic-eye cameras and related curvilinear systems. The photodetector arrays, made in planar mesh layouts with conventional techniques, are deformed and transferred onto a hemisphere. The model gives accurately the positions of photodetectors on the hemisphere, and has been validated by experiments and finite element analysis. The results also indicate very small residual strains in the photodetectors. The model provides a tool to define a pattern of photodetectors in the planar, as-fabricated layout to yield any desired spatial configuration on the hemisphere.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Bt Optoelectronic device characterization, design, and modeling

Optical properties of 1.3 μm InAs/GaAs bilayer quantum dots with high areal density

C. Y. Ngo, S. F. Yoon, D. R. Lim, Vincent Wong, and S. J. Chua

Appl. Phys. Lett. 95, 181913 (2009); http://dx.doi.org/10.1063/1.3262960 (3 pages) | Cited 5 times

Online Publication Date: 6 November 2009

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InAs/GaAs bilayer quantum dots (BQDs) are interesting structures for long wavelength emission due to its ability to tune the areal density and dot size separately. However, the need for two sets of growth rate and temperature for the respective QD layers complicates the growth procedures. Furthermore, the highest areal density reported for BQDs with 1.3 μm emission is only in the low 1010 cm−2. In this letter, we investigated the effect of GaAs spacer thickness and monolayer coverage of the active QDs on the optical properties of InAs/GaAs BQDs grown with constant growth rate and temperature. Consequently, high areal density ( ∼ 1.2×1011 cm−2) and room temperature photoluminescence emission at 1304 nm with spectral width of 24 meV was obtained.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Aging of AlGaN quantum well light emitting diode studied by scanning near-field optical spectroscopy

A. Pinos, S. Marcinkevičius, J. Yang, Y. Bilenko, M. Shatalov, R. Gaska, and M. S. Shur

Appl. Phys. Lett. 95, 181914 (2009); http://dx.doi.org/10.1063/1.3262964 (3 pages) | Cited 6 times

Online Publication Date: 6 November 2009

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Emission from a 285 nm AlGaN quantum well light emitting diode has been studied by scanning near-field optical spectroscopy. The scans revealed micrometer-size domainlike areas emitting with a higher intensity and at a longer wavelength; presumably, because of a lower AlN molar fraction in these regions. Experiments performed on different days have shown that with time, intensity from these spots increases and emission wavelength shifts to the red, indicating a further change in the quantum well alloy composition. This has allowed distinguishing an aging mechanism that involves locally increased current, heating, and atom migration.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
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Measurement of effective electron mass in biaxial tensile strained silicon on insulator

S. F. Feste, Th. Schäpers, D. Buca, Q. T. Zhao, J. Knoch, M. Bouhassoune, Arno Schindlmayr, and S. Mantl

Appl. Phys. Lett. 95, 182101 (2009); http://dx.doi.org/10.1063/1.3254330 (3 pages) | Cited 11 times

Online Publication Date: 2 November 2009

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We present measurements of the effective electron mass in biaxial tensile strained silicon on insulator (SSOI) material with 1.2 GPa stress and in unstrained SOI. Hall-bar metal oxide semiconductor field effect transistors on 60 nm SSOI and SOI were fabricated and Shubnikov–de Haas oscillations in the temperature range of T = 0.4–4 K for magnetic fields of B = 0–10 T were measured. The effective electron mass in SSOI and SOI samples was determined as mt = (0.20±0.01)m0. This result is in excellent agreement with first-principles calculations of the effective electron mass in the presence of strain.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
85.30.Tv Field effect devices
72.20.My Galvanomagnetic and other magnetotransport effects
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Negative differential resistance in conductive polymer and semiconducting quantum dot nanocomposite systems

S. Biswas, M. Dutta, and M. A. Stroscio

Appl. Phys. Lett. 95, 182102 (2009); http://dx.doi.org/10.1063/1.3258350 (3 pages) | Cited 7 times

Online Publication Date: 2 November 2009

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We report the room temperature negative differential resistance (NDR) phenomenon in nanocomposite heterostructures made of semiconducting quantum dots embedded in conductive polymers. The peak to valley ratio of the current is 91 at room temperature which increases to 2965 at 77 K. The current voltage characteristics are simulated for a double barrier resonant tunneling device formed by semiconducting quantum dots and polymer molecules. The temperature dependence is also simulated and compared with the experimental results. A close agreement is found for the experimental and the simulation results for the location of the NDR peaks.
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73.63.Kv Quantum dots
73.40.Gk Tunneling
73.23.-b Electronic transport in mesoscopic systems

Mechanism for tautomerization induced conductance switching of naphthalocyanin molecule

Qiang Fu, Jinlong Yang, and Yi Luo

Appl. Phys. Lett. 95, 182103 (2009); http://dx.doi.org/10.1063/1.3224186 (3 pages) | Cited 4 times

Online Publication Date: 3 November 2009

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Reaction mechanism for tautomerization process of a single naphthalocyanin molecule has been studied using density functional theory. It is found that tautomerization of the naphthalocyanin molecule is not a concerted reaction, but a step-wise process in that one hydrogen atom transfers after another. A stable intermediate state and the possible transition state of the reaction processes have been located. The occurrence of the intermediate state suggests that the tautomerization induced conductance switching involves four conductance states with different conductances, and the earlier proposed two-state system model is not valid.
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82.30.Qt Isomerization and rearrangement
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Uv Stochastic theories of rate constants

Design of graphene electronic devices using nanoribbons of different widths

G. G. Naumis, M. Terrones, H. Terrones, and L. M. Gaggero-Sager

Appl. Phys. Lett. 95, 182104 (2009); http://dx.doi.org/10.1063/1.3257731 (3 pages) | Cited 2 times

Online Publication Date: 5 November 2009

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We present a simple design of a field effect transistor based on graphene nanoribbons, taking advantage of the metallic and semiconductor nature of nanoribbons with different widths. Such device could be constructed by using lithography techniques. The conductance of the proposed device is obtained by using the Kubo formula, assuming a strong damping due to the substrate and imperfections of the lattice. By removing the control electrodes, the design could also be used as an electrical resistance.
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85.30.Tv Field effect devices
81.16.Nd Micro- and nanolithography

Investigation of electron wave function hybridization in Ga0.25In0.75As/InP arrays

T. P. Martin, M. S. Fairbanks, B. C. Scannell, C. A. Marlow, H. Linke, and R. P. Taylor

Appl. Phys. Lett. 95, 182105 (2009); http://dx.doi.org/10.1063/1.3258495 (3 pages) | Cited 1 time

Online Publication Date: 5 November 2009

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We present a measurement technique for quantifying coupling between semiconductor quantum dots in an array. This technique employs magnetoconductance fluctuations to probe the decrease in the average spacing of the quantum energy levels as the electron wave functions in the dots undergo hybridization. Focusing on Ga0.25In0.75As dots, we investigate hybridization as the coupling strength is varied and the number of dots in the array is increased. Our technique reveals a significant drop in the average energy level spacing for multiple dot arrays, which is strong evidence for wave function hybridization.
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73.21.La Quantum dots
73.63.Kv Quantum dots
72.20.My Galvanomagnetic and other magnetotransport effects

Large electromechanical coupling factor film bulk acoustic resonator with X-cut LiNbO3 layer transfer

M. Pijolat, S. Loubriat, S. Queste, D. Mercier, A. Reinhardt, E. Defaÿ, C. Deguet, L. Clavelier, H. Moriceau, M. Aïd, and S. Ballandras

Appl. Phys. Lett. 95, 182106 (2009); http://dx.doi.org/10.1063/1.3258496 (3 pages) | Cited 4 times

Online Publication Date: 5 November 2009

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As layer transfer techniques have been notably improved in the past years, lithium niobate (LiNbO3) appears as a candidate for the next generation of ultrawide band radio frequency (rf) filters. Depending on the crystalline orientation, LiNbO3 can achieve electromechanical coupling factors Kt2 more than six times larger than those of sputtered aluminum nitride films. In this letter, a process based on direct bonding, grinding, polishing, and deep reactive ion etching is proposed to fabricate a single crystal LiNbO3 film bulk acoustic resonator. From the fabricated test vehicles, Kt2 of 43% is measured confirming the values predicted by theoretical computations.
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77.65.Fs Electromechanical resonance; quartz resonators
81.65.Cf Surface cleaning, etching, patterning
81.65.Ps Polishing, grinding, surface finishing

Observation of the zero-magnetic-field exciton spin splitting in high quality bulk GaAs and AlGaAs

E. V. Kozhemyakina, K. S. Zhuravlev, A. Amo, D. Ballarini, and L. Viña

Appl. Phys. Lett. 95, 182107 (2009); http://dx.doi.org/10.1063/1.3257369 (3 pages) | Cited 1 time

Online Publication Date: 6 November 2009

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We present an experimental study of the zero-magnetic-field exciton spin splitting measured by time-resolved photoluminescence in high purity bulk GaAs and AlGaAs samples. The dynamics of the splitting differs from that observed in two dimensions. Initially, the splitting increases during 100–250 ps and then decays. This initial increase is attributed to the fast rise of the density of excitons formed from noncorrelated e-h pairs. The splitting dynamics is used to determine the exciton formation time, which is found to vary with excitation density from 70 to 360 ps.
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71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors

Accelerated interface defect removal in amorphous/crystalline silicon heterostructures using pulsed annealing and microwave heating

T. F. Schulze, H. N. Beushausen, T. Hansmann, L. Korte, and B. Rech

Appl. Phys. Lett. 95, 182108 (2009); http://dx.doi.org/10.1063/1.3255018 (3 pages) | Cited 6 times

Online Publication Date: 6 November 2009

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We present postdeposition annealing experiments on undoped amorphous-/n-type crystalline silicon [(i)a-Si:H/(n)c-Si/(i)a-Si:H] heterostructures used as precursors for a-Si:H/c-Si high-efficiency solar cells. Comparing conventional hotplate-heating with pulsed microwave-heating we obtain excellent interface passivation and demonstrate that microwave annealing proceeds significantly faster. The effect is ascribed to the details of microwave absorption, which selectively affects Si–H bonds and thus facilitates hydrogen bond reconfiguration needed for interface passivation. Infrared absorption spectroscopy shows that the main contribution to passivation is not stemming from bulk hydrogen reconfiguration. This suggests a hydrogen-rich interface layer, whose occurrence depends on a-Si:H deposition conditions, to be responsible for the fast annealing.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.Cc Kinetics of defect formation and annealing
73.61.Cw Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
78.66.Jg Amorphous semiconductors; glasses
81.05.Gc Amorphous semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
81.65.Rv Passivation
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Field dependence of barrier heights and luminescence properties in polar and nonpolar InGaN/GaN single quantum wells

Hooyoung Song, Jin Soak Kim, Eun Kyu Kim, Sung-Ho Lee, and Sung-Min Hwang

Appl. Phys. Lett. 95, 182109 (2009); http://dx.doi.org/10.1063/1.3258649 (3 pages)

Online Publication Date: 6 November 2009

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The external field dependence of barrier heights and the internal field dependence of luminescence properties in InxGa1−xN/GaN single quantum wells (SQWs) with polar (x = 0.13) and nonpolar (x = 0.15) orientations were investigated. The conduction band offset of a SQW was characterized by using deep level transient spectroscopy. At a reverse bias of −3 V, the barrier height of the nonpolar SQW was estimated to be 0.42 eV, which is smaller than the 0.60 eV seen in the polar SQW due to the absence of internal fields along the nonpolar direction. Both samples showed a redshift of barrier heights with increasing reverse bias. The carrier recombination affected by carrier localization, quantum-confined Stark effect, and Varshni’s shift was analyzed through temperature-dependent photoluminescence. Numerical simulations of the barrier heights and internal fields showed good agreement with experimental results.
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78.67.De Quantum wells
71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors
73.21.Fg Quantum wells
73.63.Hs Quantum wells
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Time domain analyses of the converse magnetoelectric effect in a multiferroic metallic glass-relaxor ferroelectric heterostructure

Yajie Chen, Anton L. Geiler, Trifon Fitchorov, Carmine Vittoria, and V. G. Harris

Appl. Phys. Lett. 95, 182501 (2009); http://dx.doi.org/10.1063/1.3258023 (3 pages) | Cited 17 times

Online Publication Date: 3 November 2009

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The dynamic time domain response of the converse magnetoelectric effect in a multiferroic Metglas®/Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) heterostructure, under the application of a square waveform electric field excitation of 8 kV/cm at a frequency of 0.4 Hz, is reported. The relaxation behavior followed a stretched power-law function allowing the calculation of an intrinsic time constant. Aging behavior of magnetoelectric coupling was observed after polarization switching of 1000 cycles. These phenomena are predominantly attributed to the temporal response of polarization within the PMN-PT crystal. Results elucidate the dynamic properties of relaxor-based multiferroic heterostructures and importantly define operational constraints for low frequency device operation.
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81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
61.43.Fs Glasses

Giant tunneling magnetoresistance up to 330% at room temperature in sputter deposited Co2FeAl/MgO/CoFe magnetic tunnel junctions

Wenhong Wang, Hiroaki Sukegawa, Rong Shan, Seiji Mitani, and Koichiro Inomata

Appl. Phys. Lett. 95, 182502 (2009); http://dx.doi.org/10.1063/1.3258069 (3 pages) | Cited 36 times

Online Publication Date: 3 November 2009

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Magnetoresistance ratio up to 330% at room temperature (700% at 10 K) has been obtained in a spin-valve-type magnetic tunnel junction (MTJ) consisting of a full-Heusler alloy Co2FeAl electrode and a MgO tunnel barrier fabricated on a single crystal MgO (001) substrate by sputtering method. The output voltage of the MTJ at one-half of the zero-bias value was found to be as high as 425 mV, which is the largest reported to date in MTJs using Heusler alloy electrodes. The present finding suggests that Co2FeAl may be one of the most promising candidates for future spintronics devices applications.
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75.47.De Giant magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Cd Deposition by sputtering
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Coengineering of ferroelectric and exchange bias properties in BiFeO3 based heterostructures

J. Allibe, I. C. Infante, S. Fusil, K. Bouzehouane, E. Jacquet, C. Deranlot, M. Bibes, and A. Barthélémy

Appl. Phys. Lett. 95, 182503 (2009); http://dx.doi.org/10.1063/1.3247893 (3 pages) | Cited 16 times

Online Publication Date: 3 November 2009

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The magnetoelectric coupling existing in some multiferroics may allow the low-power electrical control of spintronics devices. However, room temperature magnetoelectric multiferroics are extremely rare, an exception being BiFeO3, a ferroelectric antiferromagnet. To be used for electrically controllable spintronics, BiFeO3 has to be coupled with a ferromagnetic material through an interfacial exchange interaction, and carefully engineered to show minimum leakage. Here, we propose a Mn doped/undoped bilayer strategy that allows obtaining large exchange bias as well as low leakage. This is an important step toward the manipulation of a magnetization by an electric field in a vertical geometry.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Fg Pulsed laser ablation deposition
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
75.80.+q Magnetomechanical effects, magnetostriction
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics

Direct observation of individual Barkhausen avalanches in nucleation-mediated magnetization reversal processes

Mi-Young Im, Peter Fischer, Dong-Hyun Kim, and Sung-Chul Shin

Appl. Phys. Lett. 95, 182504 (2009); http://dx.doi.org/10.1063/1.3256188 (3 pages) | Cited 8 times

Online Publication Date: 3 November 2009

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We report the scaling behavior of Barkhausen avalanches [ H. Barkhausen, Z. Phys. 20, 401 (1919) .] along the hysteresis loop of a CoCrPt alloy film with perpendicular magnetic anisotropy for every field step of 200 Oe. Individual Barkhausen avalanches are directly observed via soft x-ray microscopy with a spatial resolution of 15 nm. The Barkhausen avalanches exhibit a power-law scaling behavior, where the scaling exponent of the power-law distribution drastically changes from 1±0.04 to 1.47±0.03 as the applied field approaches the coercivity of the CoCrPt film. We infer that this is due to the coupling of adjacent domains.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.60.Jk Magnetization reversal mechanisms
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.55.jd Thickness
68.37.Yz X-ray microscopy
75.70.Ak Magnetic properties of monolayers and thin films

Low-temperature magnetotransport behaviors of heavily Mn-doped (Ga,Mn)As films with high ferromagnetic transition temperature

L. Chen, S. Yan, P. F. Xu, J. Lu, W. Z. Wang, J. J. Deng, X. Qian, Y. Ji, and J. H. Zhao

Appl. Phys. Lett. 95, 182505 (2009); http://dx.doi.org/10.1063/1.3259821 (3 pages) | Cited 23 times

Online Publication Date: 5 November 2009

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We report the low-temperature magnetotransport behaviors of (Ga,Mn)As films with the nominal Mn concentration x larger than 10%. The ferromagnetic transition temperature TC can be enhanced to 191 K after postgrowth annealing (Ga,Mn)As with x = 20%. The temperature Tm, corresponding to the resistivity minimum in the curve of resistivity versus temperature at temperature below TC, depends on Mn concentration, annealing condition, and magnetic field. Moreover, we find that the variable-range hopping may be the main conductive mechanism when temperature is lower than Tm.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Dd Nonmetallic ferromagnetic materials
73.61.Ey III-V semiconductors
75.50.Pp Magnetic semiconductors
61.72.U- Doping and impurity implantation
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Temperature- and magnetic-field-controlled magnetic pole reversal in a molecular magnetic compound

S. M. Yusuf, Amit Kumar, and J. V. Yakhmi

Appl. Phys. Lett. 95, 182506 (2009); http://dx.doi.org/10.1063/1.3259652 (3 pages) | Cited 8 times

Online Publication Date: 6 November 2009

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A highly reversible (bipolar) switching of magnetization in a Prussian blue type molecular magnet Cu0.73Mn0.77[Fe(CN)6]⋅zH2O using low magnetic fields is demonstrated. The studied molecular compound also shows both positive and negative magnetocaloric effects below its magnetic ordering temperature. A molecular field theory calculation has also been done to explain the observed temperature dependent magnetization reversal behavior. Possible applications of the magnetic pole reversal phenomenon in magnetoelectronic and magnetocaloric devices such as magnetic memory and magnetic cooling/heating based constant temperature bath have been revealed.
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75.60.Jk Magnetization reversal mechanisms
75.50.Xx Molecular magnets
75.30.Sg Magnetocaloric effect, magnetic cooling

Observation of asymmetrical pinning of domain walls in notched Permalloy nanowires using electron holography

Kai He, David J. Smith, and Martha R. McCartney

Appl. Phys. Lett. 95, 182507 (2009); http://dx.doi.org/10.1063/1.3261753 (3 pages) | Cited 6 times

Online Publication Date: 6 November 2009

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Field-driven domain-wall motion and pinning in notched Permalloy nanowires have been observed using electron holography and Lorentz microscopy. Transverse domain walls (TDWs) were identified and different aspects of their behavior, including nucleation, injection, pinning, and depinning, were studied. The relative chirality (i.e., sense of field rotation) of the notch and the nucleation pad had a major influence in determining the TDW propagation: the walls were preferentially pinned for a notch of opposite chirality, but simply passed through when the notch had the same chirality. This asymmetrical TDW pinning accounts for the observed asymmetrical hysteresis hoop.
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75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

All-optical detection of phase fronts of propagating spin waves in a Ni81Fe19 microstripe

K. Vogt, H. Schultheiss, S. J. Hermsdoerfer, P. Pirro, A. A. Serga, and B. Hillebrands

Appl. Phys. Lett. 95, 182508 (2009); http://dx.doi.org/10.1063/1.3262348 (3 pages) | Cited 15 times

Online Publication Date: 6 November 2009

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We present the determination of the wavelength and phase of propagating spin waves in magnetic microstructures made of Ni81Fe19 using the shorted end of a coplanar waveguide for local excitation. The spin wave characteristics have been measured by phase resolved Brillouin light scattering microscopy. This recently developed technique allows for the unambiguous experimental visualization of the phase structure of propagating spin waves and is employed here to magnetic microstructures. The results show an excellent agreement with the theoretically predicted spin-wave dispersion relations.
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84.40.Az Waveguides, transmission lines, striplines
75.30.Ds Spin waves
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
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