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30 Jun 2008

Volume 92, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 264101 (2008); http://dx.doi.org/10.1063/1.2951485 (3 pages)

Wei Xiang Jiang, Tie Jun Cui, Qiang Cheng, Jessie Yao Chin, Xin Mi Yang, Ruopeng Liu, and David R. Smith
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First principles molecular dynamics study of CdS nanostructure temperature-dependent phase stability

Bin Wen and Roderick V. N. Melnik

Appl. Phys. Lett. 92, 261911 (2008); http://dx.doi.org/10.1063/1.2952835 (3 pages) | Cited 11 times

Online Publication Date: 1 July 2008

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First principles molecular dynamics simulations are used to determine the relative stability of wurtzite, graphitic, and rocksalt phases of the CdS nanostructure at various temperatures. Our results indicate that in the temperature range from 300 to 450 K, the phase stability sequence for the CdS nanostructure is rocksalt, wurtzite, and graphitic phases. The same situation holds for bulk CdS crystals under high pressure and 0 K. Our work also demonstrates that although the temperature can affect the total energy of the CdS nanostructure, it cannot change its phase stability sequence in the temperature range studied in this letter.
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71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.15.Nc Total energy and cohesive energy calculations

Effects of hydrogen on the optical properties of ZnCdO/ZnO quantum wells grown by molecular beam epitaxy

I. A. Buyanova, X. J. Wang, G. Pozina, W. M. Chen, W. Lim, D. P. Norton, S. J. Pearton, A. Osinsky, J. W. Dong, and B. Hertog

Appl. Phys. Lett. 92, 261912 (2008); http://dx.doi.org/10.1063/1.2953178 (3 pages) | Cited 7 times

Online Publication Date: 1 July 2008

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Temperature-dependent cw- and time-resolved photoluminescence (PL), as well as optically detected magnetic resonance (ODMR) measurements are employed to evaluate effects of deuterium (2H) doping on optical properties of ZnCdO/ZnO quantum well structures grown by molecular beam epitaxy. It is shown that incorporation of 2H from a remote plasma causes a substantial improvement in radiative efficiency of the investigated structures. Based on transient PL measurements, the observed improvements are attributed to efficient passivation by hydrogen of competing nonradiative recombination centers via defects. This conclusion is confirmed from the ODMR studies.
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78.67.De Quantum wells
78.55.Et II-VI semiconductors
78.47.D- Time resolved spectroscopy (>1 psec)
61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Rv Passivation

Transverse vibrations driven negative thermal expansion in a metallic compound GdPd3B0.25C0.75

Abhishek Pandey, Chandan Mazumdar, R. Ranganathan, S. Tripathi, D. Pandey, and S. Dattagupta

Appl. Phys. Lett. 92, 261913 (2008); http://dx.doi.org/10.1063/1.2953175 (3 pages) | Cited 6 times

Online Publication Date: 2 July 2008

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We have observed negative thermal expansion (NTE) in a metallic, polycrystalline, and structurally ordered cubic compound GdPd3B0.25C0.75. Our analysis suggest that the NTE observed in this compound does not stems from valence or magnetic instability of lattice ions, which is in general the case of metallic compounds exhibiting such an anomaly. We propose a possible alternative mechanism, namely, the transverse vibrations at low temperatures arising from site anisotropy, that induce the lattice contraction thereby resulting in isotropic NTE. The observed NTE also reflects its effect on the electrical transport properties of this compounds.
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65.40.De Thermal expansion; thermomechanical effects

[0001] composition modulations in Al0.4Ga0.6N layers grown by molecular beam epitaxy

A. Wise, R. Nandivada, B. Strawbridge, R. Carpenter, N. Newman, and S. Mahajan

Appl. Phys. Lett. 92, 261914 (2008); http://dx.doi.org/10.1063/1.2953451 (3 pages) | Cited 3 times

Online Publication Date: 3 July 2008

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Al0.4Ga0.6N layers grown by molecular beam epitaxy on (0001) AlN/sapphire composite substrates were examined using transmission electron microscopy. The layers show modulated structures consisting of Al-rich and Ga-rich regions. 1:1 atomic ordering on the (0001) planes was not observed. To rationalize the formation of modulations, we invoke the presence of phase separation induced Al-rich and Ga-rich regions at the AlGaN/composite interface, the development of surface undulations due to the presence of two-dimensional stresses between these regions and asymmetry in the wetting characteristics of the Al-rich and Ga-rich regions. Arguments are also developed to explain the absence of 1:1 ordering in these layers.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.37.Lp Transmission electron microscopy (TEM)
64.75.Qr Phase separation and segregation in semiconductors
68.08.Bc Wetting

Optical property and electronic band structure of a piezoelectric compound Ga3PO7 studied by the first-principles calculation

Z. X. Cheng and X. L. Wang

Appl. Phys. Lett. 92, 261915 (2008); http://dx.doi.org/10.1063/1.2955827 (3 pages)

Online Publication Date: 3 July 2008

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The structure, electronic, and optical properties of a piezoelectric material, Ga3PO7, were studied by first-principles calculations in the framework of density functional theory. The calculated structure is in agreement with the experimental data. Band structure reveals that Ga3PO7 has a band gap of 3.69 eV. Analysis of partial density of states and Mulliken charge population indicates existence of GaO5 and PO4 anion groups in Ga3PO7. Furthermore, its optical properties, including dielectric constant, absorption, reflectivity, refractive index, and electron loss were calculated and analyzed, which show that Ga3PO7 has potential applications based on combination of its piezoelectric and optical properties.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
77.22.Ch Permittivity (dielectric function)

Surface electronic properties of ZnO nanoparticles

Cuong Ton-That, Matthew R. Phillips, Matthew Foley, Steve J. Moody, and Anton P. J. Stampfl

Appl. Phys. Lett. 92, 261916 (2008); http://dx.doi.org/10.1063/1.2952955 (3 pages) | Cited 9 times

Online Publication Date: 3 July 2008

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The surface electronic structure of ZnO nanoparticles has been studied with photoemission and x-ray absorption spectroscopies. Contrary to expectation, ZnO:Zn phosphor nanoparticles were found to contain a lower oxygen vacancy density on the surface than undoped ZnO counterparts, but oxygen vacancies are in different chemical environments. Cathodoluminescence shows intense green luminescence from the ZnO:Zn surface, while the undoped nanoparticles exhibit only the near-band-edge emission. The results indicate the roles of surface oxygen vacancies and their environment in the previously unexplained green luminescence from the ZnO:Zn material.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.-f Electronic structure of nanoscale materials and related systems
73.20.At Surface states, band structure, electron density of states
78.70.Dm X-ray absorption spectra
78.60.Hk Cathodoluminescence, ionoluminescence
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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Band offset of InGaAs(N)/GaAs interfaces from first principles

Hannu-Pekka Komsa, Eero Arola, and Tapio T. Rantala

Appl. Phys. Lett. 92, 262101 (2008); http://dx.doi.org/10.1063/1.2936074 (3 pages) | Cited 2 times

Online Publication Date: 30 June 2008

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Valence-band offsets of the InGaAs/GaAs(001) and InGaAsN/GaAs(001) interfaces are calculated from first principles. For InGaAs, we study the concentrations up to 25% of indium and for InGaAsN up to 12.5% of indium with 3% of nitrogen. Even though the band offset of the InGaAs/GaAs interface has a nearly linear dependence on the indium concentration, band offset of the InGaAsN/GaAs interface is strongly influenced by the amount of In–N bonds. Even a type-II band offset is found in the case of all indium located near to nitrogen and low strain of the InGaAsN layer.
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71.20.Nr Semiconductor compounds
73.20.-r Electron states at surfaces and interfaces
71.15.-m Methods of electronic structure calculations

Capacitance transient and current-/capacitance-voltage study of direct silicon bonded (110)/(100) interface

Xuegong Yu, Jinggang Lu, and George Rozgonyi

Appl. Phys. Lett. 92, 262102 (2008); http://dx.doi.org/10.1063/1.2952513 (3 pages) | Cited 7 times

Online Publication Date: 30 June 2008

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This letter has developed a procedure for quantitatively evaluating the electrical levels at a (110)/(100) interfacial grain boundary (GB) in p-type direct silicon bonded wafers by combining current-/capacitance-voltage (I-V,C-V) and capacitance transient techniques. It is found that GB states can be positively charged and induce a high potential barrier. The local distribution of charge density deduced from I-V/C-V measurements shows that the state density is constant, ∼ 2×1012 cm−2, in the energy range Ev+0.36–0.50 eV. Meanwhile, capacitance transient technique reveals the states in the energy range Ev+0.33–0.43 eV with capture cross sections of 10−17 cm2, and the state density is consistent with the results by I-V/C-V deconvolution.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.At Surface states, band structure, electron density of states

Comparison of leakage behaviors in p- and n-type metal-oxide-semiconductor capacitors with hafnium silicon oxynitride gate dielectric by electron-beam-induced current

Jun Chen, Takashi Sekiguchi, Naoki Fukata, Masami Takase, Toyohiro Chikyo, Kikuo Yamabe, Ryu Hasunuma, Motoyuki Sato, Yasuo Nara, and Keisaku Yamada

Appl. Phys. Lett. 92, 262103 (2008); http://dx.doi.org/10.1063/1.2952829 (3 pages) | Cited 1 time

Online Publication Date: 30 June 2008

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The gate leakage behaviors of p- and n-type metal-oxide-semiconductor (p−/nMOS) capacitors with hafnium silicon oxynitride (HfSiON) gate dielectric were microscopically investigated by electron-beam-induced current (EBIC) technique. Carrier separated EBIC measurement has found that in nonstressed samples, hole conduction in pMOS is significantly enhanced by trap-assisted tunneling, while electron conduction in nMOS is independent of traps. After voltage stress, traps are induced in nMOS and enhanced electron conduction.
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84.32.Tt Capacitors
85.30.Tv Field effect devices

Electromigration induced high fraction of compound formation in SnAgCu flip chip solder joints with copper column

Luhua Xu, Jung-Kyu Han, Jarrett Jun Liang, K. N. Tu, and Yi-Shao Lai

Appl. Phys. Lett. 92, 262104 (2008); http://dx.doi.org/10.1063/1.2953692 (3 pages) | Cited 7 times

Online Publication Date: 1 July 2008

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To overcome the effect of current crowding on electromigration-induced pancake-type void formation in flip chip solder joints, two types of Cu column in 90 μm flip chip SnAgCu solder joints have been studied. They were (1) the solder contacts the Cu column at bottom and side walls and (2) the solder wets only the bottom surface of the copper column. With a current density of 1.6×104 A/cm2 at 135 °C, no failure was detected after 1290 h. However, the resistance increased by about 10% due to the formation of a large fraction of intermetallic compounds. We found that electromigration has accelerated the consumption rate of copper column and converted almost the entire solder joint into intermetallic compound. Mechanically, drop impact test indicates a brittle fracture failure in the intermetallic. The electromigration critical product for the intermetallic is discussed.
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81.20.Vj Joining; welding
66.30.Qa Electromigration

Influence of bismuth incorporation on the valence and conduction band edges of GaAs1−xBix

G. Pettinari, A. Polimeni, M. Capizzi, J. H. Blokland, P. C. M. Christianen, J. C. Maan, E. C. Young, and T. Tiedje

Appl. Phys. Lett. 92, 262105 (2008); http://dx.doi.org/10.1063/1.2953176 (3 pages) | Cited 18 times

Online Publication Date: 1 July 2008

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We investigate the electronic properties of GaAs1−xBix by photoluminescence at variable temperature (T = 10–430 K) and high magnetic field (B = 0–30 T). In GaAs0.981Bi0.019, localized state contribution to PL is dominant up to 150 K. At T = 180 K the diamagnetic shift of the free-exciton states reveals a sizable increase in the carrier effective mass with respect to GaAs. Such an increase cannot be accounted for by an enhanced localized character of the valence band states, solely. Instead, it suggests that also the Bloch states of the conduction band are heavily affected by the presence of bismuth atoms.
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73.20.At Surface states, band structure, electron density of states
78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
71.35.-y Excitons and related phenomena
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Extraordinary electroconductance in metal-semiconductor hybrid structures

Yun Wang, A. K. M. Newaz, Jian Wu, S. A. Solin, V. R. Kavasseri, N. Jin, I. S. Ahmed, and I. Adesida

Appl. Phys. Lett. 92, 262106 (2008); http://dx.doi.org/10.1063/1.2955503 (3 pages) | Cited 6 times

Online Publication Date: 2 July 2008

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We report the phenomenon of extraordinary electroconductance in microscopic metal-semiconductor hybrid structures fabricated from GaAs epitaxial layer and a Ti thin film shunt. Four-lead Van der Pauw structures show a gain of 5.2% in electroconductance under +2.5 kV/cm with zero shunt bias. The increase in the sample conductance results from the thermionic field emission of electrons and the geometrical amplification. A model provides good agreement with the experimental data and clearly demonstrates the geometry dependence of the field effect in extraordinary electroconductance (EEC). The differences between EEC devices and field effect transistors, such as junction field effect transistor (FET) and Schottky barrier gate FET, are discussed.
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73.40.Ns Metal-nonmetal contacts
79.40.+z Thermionic emission
79.70.+q Field emission, ionization, evaporation, and desorption
85.30.Tv Field effect devices

Controlled fabrication of single electron transistors from single-walled carbon nanotubes

Paul Stokes and Saiful I. Khondaker

Appl. Phys. Lett. 92, 262107 (2008); http://dx.doi.org/10.1063/1.2955520 (3 pages) | Cited 5 times

Online Publication Date: 3 July 2008

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Single electron transistors (SETs) are fabricated by placing single-walled carbon nanotubes (SWNTs) on a 100 nm wide local Al/Al2O3 bottom gate and then contacting with Pd electrodes. Coulomb oscillations up to 125 K were observed and charging energies of 12–15 meV with level spacing of ∼ 5 meV were measured from the Coulomb diamond, in agreement with a dot size of ∼ 100 nm, implying that the local gate defines the dot size by bending SWNT at the edges and controls its operation. This “mechanical template” approach may facilitate large scale fabrication of SET devices using SWNT.
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85.35.Kt Nanotube devices
85.35.Gv Single electron devices

Efficient electrical detection of ambipolar acoustic transport in GaAs

P. D. Batista, R. Hey, and P. V. Santos

Appl. Phys. Lett. 92, 262108 (2008); http://dx.doi.org/10.1063/1.2955522 (3 pages) | Cited 3 times

Online Publication Date: 3 July 2008

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We demonstrate a photon detector combining the ambipolar transport of electrons and holes by surface acoustic waves with electrical charge detection using a lateral p-i-n junction. By optimizing photon absorption and the acoustic transport, overall quantum efficiencies of 70% have been achieved for ambipolar transport lengths exceeding 100 μm.
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43.58.-e Acoustical measurements and instrumentation
43.60.Vx Acoustic sensing and acquisition
68.35.Iv Acoustical properties

Epitaxial growth and surface metallic nature of LaNiO3 thin films

K. Tsubouchi, I. Ohkubo, H. Kumigashira, Y. Matsumoto, T. Ohnishi, M. Lippmaa, H. Koinuma, and M. Oshima

Appl. Phys. Lett. 92, 262109 (2008); http://dx.doi.org/10.1063/1.2955534 (3 pages) | Cited 15 times

Online Publication Date: 3 July 2008

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In situ epitaxial growth control of LaNiO3 (LNO) films at high oxygen pressure has been successfully achieved using a combination of pulsed laser deposition and high-pressure reflection high-energy electron diffraction (RHEED). RHEED oscillations, indicative of epitaxial layer-by-layer growth, were clearly observed during LNO deposition under optimal conditions. The film surfaces were composed of atomically flat terraces and steps. Detailed photoelectron spectroscopy analysis of LNO grown at the optimal oxygen pressure revealed that Ni ions assume a uniform Ni3+ high-valence state and that the resultant metallic properties are preserved even at the surface and in the interface region between LNO and the LaAlO3 substrate.
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68.55.aj Insulators
81.15.Fg Pulsed laser ablation deposition
75.70.Ak Magnetic properties of monolayers and thin films
75.20.Ck Nonmetals
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Stable response to visible light of InGaN photoelectrodes

Wenjun Luo, Bin Liu, Zhaosheng Li, Zili Xie, Dunjun Chen, Zhigang Zou, and Rong Zhang

Appl. Phys. Lett. 92, 262110 (2008); http://dx.doi.org/10.1063/1.2955828 (3 pages) | Cited 9 times

Online Publication Date: 3 July 2008

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The photoelectrochemical properties of InxGa1−xN/GaN (0 ⩽ x ⩽ 0.20) epitaxial films on sapphire (0001) substrates have been investigated. The flatband potential of InxGa1−xN is shifted to more positive voltages with increasing indium incorporation. In aqueous HBr solution, the turnover number of the In0.20Ga0.80N electrode reaches 847 after 4000 s illumination, which suggests that In0.20Ga0.80N has good photostability. Moreover, In0.20Ga0.80N shows highest visible-light response among InxGa1−xN (0 ⩽ x ⩽ 0.20) and the incident photon conversion efficiency is about 9% at 400–430 nm in the HBr solution.
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78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
82.45.Vp Semiconductor materials in electrochemistry
82.45.Fk Electrodes
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Conversion electron Mössbauer spectroscopy of epitaxial Co2Cr0.6Fe0.4Al thin films

Vadim Ksenofontov, Christian Herbort, Martin Jourdan, and Claudia Felser

Appl. Phys. Lett. 92, 262501 (2008); http://dx.doi.org/10.1063/1.2952760 (3 pages) | Cited 14 times

Online Publication Date: 30 June 2008

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Heusler half-metals are promising for spintronic applications. Epitaxial thin films of the exemplar compound Co2Cr0.6Fe0.4Al (CCFA) were investigated using conversion electron Mössbauer spectroscopy to clarify the factors influencing the spin polarization. CCFA films were deposited by rf magnetron sputtering on MgO substrates with and without an Fe buffer layer. Annealing improves their crystallographic order, causes the diffusion of Fe atoms from the Fe buffer layer into the CCFA, and favors the Co–Fe disorder. The listed factors are possible reasons for the increase and subsequent reduction of the tunneling magnetoresistance in CCFA thin films observable across the annealing temperature range.
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75.70.Ak Magnetic properties of monolayers and thin films
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.47.Np Metals and alloys
72.25.-b Spin polarized transport
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology

Giant microwave tunability in FeGaB/lead magnesium niobate-lead titanate multiferroic composites

J. Lou, D. Reed, C. Pettiford, M. Liu, P. Han, S. Dong, and N. X. Sun

Appl. Phys. Lett. 92, 262502 (2008); http://dx.doi.org/10.1063/1.2952828 (3 pages) | Cited 17 times

Online Publication Date: 30 June 2008

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Giant magnetoelectric coupling at both microwave frequencies and dc was observed in an FeGaB/lead magnesium niobate-lead titanate microwave multiferroic composite. A record high microwave frequency tunability of Δf = 900 MHz or Δf/f = 58% was demonstrated with the change of an external electric field from −6 to +2 kV/cm. A strong electric field dependence of magnetic hysteresis loops was also observed. Such multiferroic composite provides great opportunities for electrostatically tunable microwave devices.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.-y Studies of specific magnetic materials
77.80.-e Ferroelectricity and antiferroelectricity
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Extrinsic origin of ferromagnetism in single crystalline LaAlO3 substrates and oxide films

F. Golmar, A. M. Mudarra Navarro, C. E. Rodríguez Torres, F. H. Sánchez, F. D. Saccone, P. C. dos Santos Claro, G. A. Benítez, and P. L. Schilardi

Appl. Phys. Lett. 92, 262503 (2008); http://dx.doi.org/10.1063/1.2952839 (3 pages) | Cited 17 times

Online Publication Date: 30 June 2008

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Commercial LaAlO3 substrates were thermally cycled simulating a procedure similar to those followed during TiO2 and SnO2 dilute magnetic semiconductors’ film pulsed laser deposition. Ferromagneticlike behavior was found in some substrates, in which metallic iron impurities were detected by x-ray photoelectron spectroscopy and total reflection x-ray fluorescence measurements. A thorough experimental investigation, using high resolution techniques, showed that these impurities were introduced by the procedure used to fix the substrates to the oven silicon holders. It is suggested that magnetism observed previously in nominally pure SnO2 films is of extrinsic origin.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
79.60.Dp Adsorbed layers and thin films
78.55.Hx Other solid inorganic materials
78.70.En X-ray emission spectra and fluorescence

Size dependence of intrinsic spin transfer switching current density in elliptical spin valves

R. Heindl, S. E. Russek, T. J. Silva, W. H. Rippard, J. A. Katine, and M. J. Carey

Appl. Phys. Lett. 92, 262504 (2008); http://dx.doi.org/10.1063/1.2953980 (3 pages) | Cited 6 times

Online Publication Date: 2 July 2008

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We studied current-induced magnetization reversal in elliptical spin valves with CoFeB free layers. The data obtained from high-speed pulsed switching experiments showed that the intrinsic switching current densities were size dependent and 50%–100% higher than predicted by a single-domain model. Micromagnetic simulations reveal a complex behavior of magnetization switching in which end-mode oscillations are important, and indicate that the switching current density depends on the device dimensions. Experimental values for the intrinsic switching current density agree with those predicted by micromagnetic simulations.
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75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Three-dimensional magnetic microstructures fabricated by microstereolithography

Kengo Kobayashi and Koji Ikuta

Appl. Phys. Lett. 92, 262505 (2008); http://dx.doi.org/10.1063/1.2954011 (3 pages) | Cited 6 times

Online Publication Date: 2 July 2008

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Our group has developed a magnetically modified photocurable polymer for use in microstereolithography to fabricate magnetic microstructures and microactuators having three-dimensionally complex structures. This polymer is prepared by mixing a photocurable polymer with magnetic particles together with a viscosity-increasing agent for preserving the dispersion of the particles. In this study, we conducted experiments to evaluate the curing and magnetic characteristics of this magnetically modified photocurable polymer. We then rapidly fabricated truly three-dimensional magnetic microstructures by microstereolithography using this polymer. We expect that this achievement will lead to the development of magnetic microactuators.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Multiferroicity in the spin-1/2 quantum matter of LiCu2O2

A. Rusydi, I. Mahns, S. Müller, M. Rübhausen, S. Park, Y. J. Choi, C. L. Zhang, S.-W. Cheong, S. Smadici, P. Abbamonte, M. v. Zimmermann, and G. A. Sawatzky

Appl. Phys. Lett. 92, 262506 (2008); http://dx.doi.org/10.1063/1.2787973 (3 pages) | Cited 16 times

Online Publication Date: 2 July 2008

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Multiferroicity in LiCu2O2 single crystals is studied using resonant soft x-ray magnetic scattering, hard x-ray diffraction, heat capacity, magnetic susceptibility, and electrical polarization. Two magnetic transitions are found at 24.6 K (T1) and 23.2 K (T2). Our data are consistent with a sinusoidal spin structure at T2<T<T1 and with a helicoidal spin structure at T<T2, giving rise to ferroelectricity. Surprisingly, above T2, the correlation lengths of the spin structures increase as the temperature increases with dramatic changes of ∼ 42% occurring along the c axis.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Influence of asymmetry on vortex nucleation and annihilation in submicroscaled permalloy disk array

Kuo-Ming Wu, Lance Horng, Jia-Feng Wang, Jong-Ching Wu, Yin-Hao Wu, and Ching-Ming Lee

Appl. Phys. Lett. 92, 262507 (2008); http://dx.doi.org/10.1063/1.2946495 (3 pages) | Cited 7 times

Online Publication Date: 2 July 2008

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Magnetic properties of vortex nucleation, annihilation, and switching field distribution (SFD) in NiFe disk arrays, where the elements are with 300 nm diameter and different degrees of asymmetry, were investigated through measurements and simulations of hysteresis loop. The nucleation and annihilation of vortex state show strong dependences on the asymmetry. More interestingly, the width of SFD, the crucial factor for high-density storage application, oscillating with the degree of asymmetry is observed. The simulation results agree well with the experimental data.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Mg Numerical simulation studies
75.50.Bb Fe and its alloys

Spin-torque oscillator with tilted fixed layer magnetization

Yan Zhou, C. L. Zha, S. Bonetti, J. Persson, and Johan Åkerman

Appl. Phys. Lett. 92, 262508 (2008); http://dx.doi.org/10.1063/1.2955831 (3 pages) | Cited 30 times

Online Publication Date: 3 July 2008

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A spin-torque oscillator with a fixed layer magnetization tilted out of the film plane is capable of strong microwave signal generation in zero magnetic field. Through numerical simulations, we study the microwave signal generation as a function of drive current for two realistic tilt angles. The tilted magnetization of the fixed layer can be achieved by using a material with high out-of-plane magnetocrystalline anisotropy, such as L10 FePt.
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84.30.Ng Oscillators, pulse generators, and function generators
84.40.-x Radiowave and microwave (including millimeter wave) technology
02.60.-x Numerical approximation and analysis

Relation between magnetoresistance and nanostructure of current-perpendicular-to-plane giant-magnetoresistance film with current-confined-path nano-oxide layer

Hiromi Yuasa, Michiko Hara, and Hideaki Fukuzawa

Appl. Phys. Lett. 92, 262509 (2008); http://dx.doi.org/10.1063/1.2952773 (3 pages) | Cited 4 times

Online Publication Date: 3 July 2008

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Nanostructure of a current-perpendicular-to-plane giant-magnetoresistance film with a current-confined-path (CCP) nano-oxide layer was analyzed by high-resolution transmission electron microscopy and three-dimensional atom probe. It was found that the CCP of a film with a higher magnetoresistance (MR) ratio has better crystalline orientation and higher purity than the CCP of a film with a smaller MR ratio. Moreover, the free layer on the CCP of a film with a high MR ratio is well crystallized. Both the CCP with the good crystalline orientation and high purity and the well-crystallized free layer diminish the diffusive electron scattering, which improves an MR ratio.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
75.47.De Giant magnetoresistance
75.50.Tt Fine-particle systems; nanocrystalline materials
68.55.-a Thin film structure and morphology
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