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1 Aug 2011

Volume 99, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 051112 (2011); http://dx.doi.org/10.1063/1.3617421 (3 pages)

Wei Li, Jun Chen, Gerard Nouet, Liang-yao Chen, and Xunya Jiang
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Response of graphene to femtosecond high-intensity laser irradiation

Adam Roberts, Daniel Cormode, Collin Reynolds, Ty Newhouse-Illige, Brian J. LeRoy, and Arvinder S. Sandhu

Appl. Phys. Lett. 99, 051912 (2011); http://dx.doi.org/10.1063/1.3623760 (3 pages) | Cited 13 times

Online Publication Date: 4 August 2011

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We study the response of graphene to high-intensity, 50-femtosecond laser pulse excitation. We establish that graphene has a high (∼3 × 1012 Wcm−2) single-shot damage threshold. Above this threshold, a single laser pulse cleanly ablates graphene, leaving microscopically defined edges. Below this threshold, we observe laser-induced defect formation leading to degradation of the lattice over multiple exposures. We identify the lattice modification processes through in-situ Raman microscopy. The effective lifetime of chemical vapor deposition grown graphene under femtosecond near-infrared irradiation and its dependence on laser intensity is determined. These results also define the limits of non-linear applications of graphene in femtosecond high-intensity regime.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.30.Am Elemental semiconductors and insulators
78.47.J- Ultrafast spectroscopy (<1 psec)
78.67.Wj Optical properties of graphene

Femtosecond ultrasonic spectroscopy using a piezoelectric nanolayer: Hypersound attenuation in vitreous silica films

Yu-Chieh Wen, Shi-Hao Guol, Hung-Pin Chen, Jinn-Kong Sheu, and Chi-Kuang Sun

Appl. Phys. Lett. 99, 051913 (2011); http://dx.doi.org/10.1063/1.3620879 (3 pages) | Cited 2 times

Online Publication Date: 4 August 2011

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We report ultra-broadband ultrasonic spectroscopy with an impedance-matched piezoelectric nanolayer, which enables optical generation and detection of a 730-fs acoustic pulse (the width of ten lattice constants). The bandwidth improvement facilitates THz laser ultrasonics to bridge the spectral gap between inelastic light and x-ray scatterings (0.1-1 THz) in the studies of lattice dynamics. As a demonstration, this method is applied to measure sound attenuation α in a vitreous SiO2 thin film. Our results extend the existing low-frequency data obtained by ultrasonic-based and light scattering methods and also show a α∝ f2 behavior for frequencies f up to 650 GHz.
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62.65.+k Acoustical properties of solids
68.60.Bs Mechanical and acoustical properties
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.70.Ck X-ray scattering
78.47.je Time resolved light scattering spectroscopy

Conducted growth of SrRuO3 nanodot arrays on self-ordered La0.18Sr0.82Al0.59Ta0.41O3(001) surfaces

R. Bachelet, C. Ocal, L. Garzón, J. Fontcuberta, and F. Sánchez

Appl. Phys. Lett. 99, 051914 (2011); http://dx.doi.org/10.1063/1.3622140 (3 pages) | Cited 2 times

Online Publication Date: 4 August 2011

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We show that the surface of (001)-oriented La0.18Sr0.82Al0.59Ta0.41O3 (LSAT) single-crystalline substrates can be self-ordered as to become a laterally long-range ordered pattern of nanometric stripes of distinct composition. Atomically flat and periodically modulated, the resulting surface exhibits concomitant interface energy variations with an upper growing epilayer. By exploiting combined selective growth and epitaxial strain, these nanostructured substrates are used as templates to promote the self-formation of one-dimensional arrays of SrRuO3 dots.
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81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
68.55.A- Nucleation and growth
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Surface acoustic wave response to ambient humidity in graphite oxide structures

R. Rimeika, J. Barkauskas, and D. Čiplys

Appl. Phys. Lett. 99, 051915 (2011); http://dx.doi.org/10.1063/1.3624476 (3 pages)

Online Publication Date: 5 August 2011

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The effect of ambient air humidity on surface acoustic waves (SAW) in graphite oxide-lithium niobate structures was investigated. The acoustic wave amplitude and phase strongly depended on the humidity level in structures with graphite oxide films deposited on the free substrate surface. These dependencies were significantly reduced in structures with graphite oxide films deposited on a metalized substrate surface. Fast (sub-second range) response in the acoustic amplitude and phase to step-like humidity changes was observed. Humidity-induced variations in the SAW amplitude and velocity are attributed to acoustoelectric interaction and mass loading due to moisture adsorption by graphite oxide layers.
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68.35.Iv Acoustical properties
68.43.Mn Adsorption kinetics
68.60.Bs Mechanical and acoustical properties
72.50.+b Acoustoelectric effects
73.50.Rb Acoustoelectric and magnetoacoustic effects
62.65.+k Acoustical properties of solids

Strong Faraday rotation in Ce and Bi comodified epitaxial iron garnet films: Valence control through strain engineering

Jae-Yeol Hwang, Roberto Morandotti, and Alain Pignolet

Appl. Phys. Lett. 99, 051916 (2011); http://dx.doi.org/10.1063/1.3621838 (3 pages) | Cited 3 times

Online Publication Date: 5 August 2011

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The correlation between lattice-misfit strain and the valence change of cerium was investigated in cerium and bismuth comodified iron garnet epitaxial films. We demonstrated that the transition of the valence state from Ce4+ to Ce3+ is triggered by reducing the compressive lattice-misfit strain and that the increase in concentration of Ce3+ induces a red-shift of the optical bandgap as well as an enhancement of the Faraday rotation. An extraordinary Faraday rotation of 0.91 deg/μm at 1.55 μm was achieved in these films by maximizing the concentration of Ce3+ through strain engineering.
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78.20.Ls Magneto-optical effects
78.66.Nk Insulators
71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Interface thermal resistance and thermal rectification in hybrid graphene-graphane nanoribbons: A nonequilibrium molecular dynamics study

A. Rajabpour, S. M. Vaez Allaei, and F. Kowsary

Appl. Phys. Lett. 99, 051917 (2011); http://dx.doi.org/10.1063/1.3622480 (3 pages) | Cited 12 times

Online Publication Date: 5 August 2011

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The thermal conductivity of hybrid graphene-graphane nanoribbons (GGNRs) have been investigated using nonequilibrium molecular dynamics simulations. The interface between graphene and graphane leads to a Kapitza resistance with strongly dependence on the imposed heat flux direction. We introduce GGNRs as promising thermal rectifiers at room temperature. By calculating phonon spectra, underlying mechanisms were investigated.
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73.40.Ei Rectification
31.15.xv Molecular dynamics and other numerical methods
66.70.Df Metals, alloys, and semiconductors
63.22.Rc Phonons in graphene
68.35.Ct Interface structure and roughness
68.35.Ja Surface and interface dynamics and vibrations
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Towards proper characterization of nonlinear metal-semiconductor contacts. Generalization of the transmission line method

R. Piotrzkowski, E. Litwin-Staszewska, and Sz. Grzanka

Appl. Phys. Lett. 99, 052101 (2011); http://dx.doi.org/10.1063/1.3619813 (3 pages)

Online Publication Date: 1 August 2011

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Modern optoelectronic devices are often based on wide-bandgap semiconductors such as GaN. In such cases the current injecting contacts are usually nonlinear, especially for p-type materials. Using the standard transmission line method (TLM), which gives satisfactory results in linear cases, characterization of nonlinear contacts can lead to serious ambiguities. In this Letter, we derive exact formulas permitting to extract the current-voltage characteristics of the non-linear metal–semiconductor contact from measurements performed on standard TLM pattern, as well as to simulate behavior of such pattern for given model contact characteristic. The application of this generalized TLM method is illustrated on the example of Ni/Au contacts on p-GaN
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81.05.Ea III-V semiconductors
73.40.Ns Metal-nonmetal contacts

Sub-nm equivalent oxide thickness on Si-passivated GaAs capacitors with low Dit

M. El Kazzi, L. Czornomaz, D. J. Webb, C. Rossel, D. Caimi, H. Siegwart, J. Fompeyrine, and C. Marchiori

Appl. Phys. Lett. 99, 052102 (2011); http://dx.doi.org/10.1063/1.3615680 (3 pages) | Cited 4 times

Online Publication Date: 1 August 2011

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A thin amorphous silicon interlayer, inserted between the III-V semiconductor and the gate dielectric is expected to prevent III-V oxidation, as required for high-mobility channel transistors. We demonstrate that the addition of a thin Al2O3 barrier layer between the a-Si and the high-k HfO2, together with optimized post-metallization annealing, is the key to reduce the a-Si consumption and to achieve a highly scaled gate stack with equivalent oxide thickness of ∼0.8 nm. The evolution of the interfaces during growth and the quality of the stack are investigated by in-situ X-ray photoelectron spectroscopy and electrical measurements on metal-oxide-semiconductors capacitors.
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81.05.Ea III-V semiconductors
81.65.Mq Oxidation
81.65.Rv Passivation
84.32.Tt Capacitors
85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing

Modulation of atomic-layer-deposited Al2O3 film passivation of silicon surface by rapid thermal processing

Dong Lei, Xuegong Yu, Lihui Song, Xin Gu, Genhu Li, and Deren Yang

Appl. Phys. Lett. 99, 052103 (2011); http://dx.doi.org/10.1063/1.3616145 (3 pages)

Online Publication Date: 1 August 2011

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We have investigated the effect of a thin interfacial silicon oxide on the atomic-layer-deposited Al2O3 film passivating the silicon surface based on rapid thermal process (RTP). It is found that the effective carrier lifetime of samples strongly depends on the RTP temperature and reaches the maximum value at 550 °C. Both capacitance-voltage measurements and theoretical simulation have revealed that the RTP treatment cannot only modulate the charges in the Al2O3 film but also reduce the density of interface states responsible for the surface recombination. These results are interesting for the fabrication of high efficiency silicon solar cells in photovoltaics.
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81.65.Rv Passivation
68.47.Fg Semiconductor surfaces
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Three-dimensional PN junction capacitor for passive integration

Huijuan Wang, Lixi Wan, Daquan Yu, Daniel Guidotti, Ran He, Fengwei Dai, Liqiang Cao, Xia Zhang, Ning Zhao, and Xueping Guo

Appl. Phys. Lett. 99, 052104 (2011); http://dx.doi.org/10.1063/1.3610489 (3 pages)

Online Publication Date: 2 August 2011

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A wafer level three-dimensional (3D) PN junction capacitor for passive device integration on Si is developed. The 3D capacitor structure is created by deep trench etching of Si and appropriate doping. The salient characteristics of the PN junction capacitors fabricated in this study are as follows. The maximum areal capacitance density is 11.5 fF/μm2, the highest breakdown voltage is −20 V, and the minimum leakage current is 5 nA at an applied reverse voltage of −5 V. In comparison with the planar PN junction capacitor, the 3D junction capacitor can provide 8-12 times the capacitance density at the same doping concentration.
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84.32.Tt Capacitors

Unipolar resistive switching mechanism speculated from irreversible low resistance state of Cu2O films

Sahwan Hong, Deng Xiao Long, Inrok Hwang, Jin-Soo Kim, Yun Chang Park, Sung-Oong Kang, and Bae Ho Park

Appl. Phys. Lett. 99, 052105 (2011); http://dx.doi.org/10.1063/1.3619833 (3 pages) | Cited 2 times

Online Publication Date: 4 August 2011

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We observed cathode-interfaced electroreduction and a variation of oxygen content in an irreversible low resistance state of highly oriented cuprous oxide (Cu2O) films. These local microstructural and stoichiometric changes in hard breakdown of film allow speculation on the unipolar resistive switching mechanism: formation of metallic filaments originating from generation/migration of oxygen ions (O2−) from the cathode and release of oxygen gas through the anode. Based on the as-proposed switching model, endurance switching properties could be modulated from tens up to over 104 switching cycles by controlling ambient gas or the interface between Cu2O and anode.
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84.30.Sk Pulse and digital circuits

Interaction between hydrogen and the Fe-B pair in boron-doped p-type silicon

C. K. Tang, L. Vines, B. G. Svensson, and E. V. Monakhov

Appl. Phys. Lett. 99, 052106 (2011); http://dx.doi.org/10.1063/1.3619848 (3 pages) | Cited 1 time

Online Publication Date: 4 August 2011

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The effect of hydrogen incorporation into iron-contaminated boron-doped Cz-Si has been investigated using deep level transient spectroscopy. In-diffusion of hydrogen by wet chemical etching followed by reverse bias annealing of Al, Schottky diodes result in the appearance of the defect level characteristic to interstitial iron (Fei), and the concentration of iron-boron pairs (Fe-B) decreases correspondingly. Quantitative observations from various defect concentration versus depth profiles imply strongly that H promotes dissociation of Fe-B releasing Fei whereas no detectable passivation of Fe-B or Fei by H occurs.
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71.55.Cn Elemental semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Gh Other heat and thermomechanical treatments
81.65.Cf Surface cleaning, etching, patterning
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Transport and thermoelectric properties in Copper intercalated TiS2 chalcogenide

E. Guilmeau, Y. Bréard, and A. Maignan

Appl. Phys. Lett. 99, 052107 (2011); http://dx.doi.org/10.1063/1.3621834 (3 pages) | Cited 10 times

Online Publication Date: 4 August 2011

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We report on the thermoelectric properties of CuxTiS2 bulk compounds. Copper cations have been intercalated into the layered chalcogenide TiS2 by spark plasma sintering. X-ray diffraction analysis coupled to transmission electron microscopy shows that the lattice constant c expands linearly as the Cu content x increases. The Cu-intercalation into TiS2 leads to substantial decrease in both electrical resistivity and lattice thermal conductivity as compared to those of pristine TiS2. The figure of merit, ZT, is increased up to 0.45 at 800 K for x = 0.02. The power factor, PF, reaches 1.7 mW/mK2 in TiS2 at 325 K.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
66.70.Df Metals, alloys, and semiconductors
52.77.-j Plasma applications

Atomic-layer-deposited Al2O3 on Bi2Te3 for topological insulator field-effect transistors

Han Liu and Peide D. Ye

Appl. Phys. Lett. 99, 052108 (2011); http://dx.doi.org/10.1063/1.3622306 (3 pages) | Cited 2 times

Online Publication Date: 4 August 2011

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We report dual-gate modulation of topological insulator field-effect transistors (TI FETs) made on Bi2Te3 thin flakes with integration of atomic-layer-deposited (ALD) Al2O3 high-k dielectric. Atomic force microscopy study shows that ALD Al2O3 is uniformly grown on this layer-structured channel material. Electrical characterization reveals that the right selection of ALD precursors and the related surface chemistry play a critical role in device performance of Bi2Te3 based TI FETs. We realize both top-gate and bottom-gate control on these devices, and the highest modulation rate of 76.1% is achieved by using simultaneous dual gate control.
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85.30.Tv Field effect devices
77.55.dj For nonsilicon electronics (Ge, III-V, II-VI, organic electronics)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Dual-donor codoping approach to realize low-resistance n-type ZnS semiconductor

Dengfeng Li, Bo Deng, Shuwen Xue, Zhiguo Wang, and Fei Gao

Appl. Phys. Lett. 99, 052109 (2011); http://dx.doi.org/10.1063/1.3624531 (3 pages)

Online Publication Date: 5 August 2011

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Based on first-principles calculations, we explored a good candidate for achieving low-resistance and high carrier concentration of n-type ZnS by a dual-donor codoping method, where the ionization energy was effectively reduced. We found that the SnZn-FS pair has a shallow donor level of 17.2 meV, a small formation energy of 1.27 eV and a high binding energy of 1.28 eV. The density of states analysis showed that the SnZn-FS pair induces the downward shift of the conduction band minimum by about 0.15 eV, while the basis electronic structure does not change. Thus, the SnZn-FS pair is likely to be a best n-type dopant for ZnS.
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61.72.uj III-V and II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations
71.20.Nr Semiconductor compounds
72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Ey III-V and II-VI semiconductors
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Linewidth reduction in a spin-torque nano-oscillator caused by non-conservative current-induced coupling between magnetic layers

D. Gusakova, M. Quinsat, J. F. Sierra, U. Ebels, B. Dieny, L. D. Buda-Prejbeanu, M.-C. Cyrille, V. Tiberkevich, and A. N. Slavin

Appl. Phys. Lett. 99, 052501 (2011); http://dx.doi.org/10.1063/1.3615283 (3 pages) | Cited 7 times

Online Publication Date: 1 August 2011

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We demonstrate by macrospin simulations that in a spin-torque nano-oscillator having synthetic antiferromagnet fixed layer, the non-conservative dynamic coupling between the free and fixed layers caused by spin-torque effect leads to a substantial reduction of the linewidth of the current-induced spin wave mode, involving oscillations in all three magnetic layers. By analysing the phase and amplitude noise extracted from the simulated signal, we prove that the obtained linewidth reduction is related to the reduction of the dimensionless non-linear amplitude-phase coupling parameter ν.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
84.30.Ng Oscillators, pulse generators, and function generators
85.35.-p Nanoelectronic devices

d0 ferromagnetism in undoped sphalerite ZnS nanoparticles

Daqiang Gao, Guijin Yang, Jing Zhang, Zhonghua Zhu, Mingsu Si, and Desheng Xue

Appl. Phys. Lett. 99, 052502 (2011); http://dx.doi.org/10.1063/1.3622303 (3 pages) | Cited 9 times

Online Publication Date: 1 August 2011

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We report the sulfur vacancies-related d0 ferromagnetism in undoped sphalerite ZnS nanoparticles. Systematically tune of sulfur deficiency in ZnS nanoparticles was done by selecting different synthesized temperatures and varying the ratio of hydrogen and argon in post-annealing processes. Our study suggests that such sulfur vacancies can induce the room temperature ferromagnetism. Importantly, the ferromagnetism can be modulated by changing the concentration of sulfur vacancies in the samples. This finding should be the focus of future electronic and spintronic devices.
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75.75.Cd Fabrication of magnetic nanostructures
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Magnetic phase separation in SrCoOx (2.5 ≤ x ≤ 3)

C. K. Xie, Y. F. Nie, B. O. Wells, J. I. Budnick, W. A. Hines, and B. Dabrowski

Appl. Phys. Lett. 99, 052503 (2011); http://dx.doi.org/10.1063/1.3622644 (3 pages) | Cited 2 times

Online Publication Date: 2 August 2011

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This work presents a study of the electronic phase separation resulting from oxygen non-stoichiometry in SrCoOx. We report here that for oxygen content 2.88 ≤ x ≤ 3, SrCoOx exhibits a magnetic phase separation while maintaining a single crystallographic phase. Two magnetic components are formed which match those found in SrCoO2.88 and SrCoO3 with TC = 220 K and 280 K, respectively. In addition, a value of TC = 160 K is assigned to the previously identified SrCoO2.75 phase. A magnetic phase diagram with four line phases is proposed for SrCoOx (2.5 ≤ x ≤ 3).
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Wx Spin crossover
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
61.66.Fn Inorganic compounds

Effects of nanocrystal formation on the soft magnetic properties of Fe-based bulk metallic glasses

J. E. Gao, H. X. Li, Z. B. Jiao, Y. Wu, Y. H. Chen, T. Yu, and Z. P. Lu

Appl. Phys. Lett. 99, 052504 (2011); http://dx.doi.org/10.1063/1.3621832 (3 pages) | Cited 3 times

Online Publication Date: 2 August 2011

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We developed several Fe-based bulk metallic glasses with a unique combination of large glass-forming ability and excellent soft magnetic properties by minor doping of Cu in the Fe76C7.0Si3.3B5.0P8.7 alloy. Proper additions of the non-magnetic copper element which has a positive heat of mixing with Fe, coupled with adequate annealing, can stimulate formation of ∼5 nm αFe ferromagnetic nanocrystals, which results in the increment in the saturation magnetization. Over-annealing which induced coarsening of the α-Fe nanocrystals reduces the ferromagnetic exchange interaction between the nanosized α-Fe crystals and increases the effective magneto-crystalline anisotropy, thereby deteriorating the soft magnetic properties.
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75.75.-c Magnetic properties of nanostructures
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
64.75.Ef Mixing

Ferromagnetism in C-doped SnO2 thin films

Nguyen Hoa Hong, J.-H. Song, A. T. Raghavender, T. Asaeda, and M. Kurisu

Appl. Phys. Lett. 99, 052505 (2011); http://dx.doi.org/10.1063/1.3617439 (3 pages) | Cited 14 times

Online Publication Date: 3 August 2011

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Room temperature ferromagnetism (FM) was observed in laser ablated C-doped SnO2 thin films grown on LaAlO3 substrates. The greatest value of the saturated magnetization (at 1 T) is found in SnO2 films doped with 1% of C (about 16 emu/cm3) and reduces lightly as the C concentration increases. By subtracting the base of pure SnO2 that is also magnetic, one can find that C-doping actually enhances ferromagnetism in the host SnO2. It suggests that carbon really causes defect-induced magnetism of about 3.91 μB/C into SnO2. Measurements on C-doped SnO2 bulks show that the observed properties are unique for films (lower dimensions, having surface/interface effect). The investigation on thickness dependence shows a change in magnetization when going from thin to thick films, implying that somehow if magnetism is due to defects then those must be located more on or near the surface than in deeper layers. Anisotropy is also observed, enforcing the assumption for the origin of magnetism due to defects in C-doped SnO2.
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75.70.Ak Magnetic properties of monolayers and thin films
61.72.up Other materials
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials

Spin exchange interactions in hexagonal manganites RMnO3 (R = Tb, Dy, Ho, Er) epitaxial thin films

Xiang-Bai Chen, Nguyen Thi Minh Hien, D. Lee, S.-Y. Jang, T. W. Noh, and In-Sang Yang

Appl. Phys. Lett. 99, 052506 (2011); http://dx.doi.org/10.1063/1.3622768 (3 pages) | Cited 1 time

Online Publication Date: 3 August 2011

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We present the results of an optical method of quantitatively estimating the spin exchange interactions in hexagonal manganites RMnO3 (R = Tb, Dy, Ho, Er) epitaxial thin films. The two in-plane (a-b plane) spin exchange integrals J1 (intratrimer Mn-Mn interaction) and J2 (intertrimer Mn-Mn interaction) are deduced from the magnon scattering peak wavenumbers. We found that J2 decreases systematically when the R ionic radius increases, while J1 is nearly independent of R ionic radius, contrary to the expectation in single crystals. We show that the R dependence of J1 could be understood in terms of the stress in the thin films. Our result indicates that the stress has stronger effect on the atomic displacement of the intratrimer Mn-Mn distance than the intertrimer Mn-Mn distance.
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75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
78.30.Hv Other nonmetallic inorganics
75.30.Ds Spin waves

Magnetization reversal in composition-controlled Gd1–xCox ferrimagnetic films close to compensation composition

A. Hrabec, N. T. Nam, S. Pizzini, and L. Ranno

Appl. Phys. Lett. 99, 052507 (2011); http://dx.doi.org/10.1063/1.3609860 (3 pages) | Cited 2 times

Online Publication Date: 3 August 2011

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multimedia

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We report on a model system for micromagnetic studies, i.e., ferrimagnetic Gd1−xCox thin films with controlled composition gradient and, therefore, a controlled magnetization gradient along the film. By employing extraordinary Hall effect measurements and Kerr microscopy, we have studied magnetization reversal and shown that, around compensation, varying magnetization with temperature or composition is equivalent. In particular, the coercive field diverges close to the compensation temperature or close to the compensation interface. The position of the compensation interface is very sensitive to temperature and can be used as a probe of sample heating.
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75.60.Jk Magnetization reversal mechanisms
75.70.Ak Magnetic properties of monolayers and thin films
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.61.At Metal and metallic alloys
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

A possible pressure-induced superconducting-semiconducting transition in nearly optimally doped single crystalline YBa2Cu3O7-δ

T. Muramatsu, D. Pham, and C. W. Chu

Appl. Phys. Lett. 99, 052508 (2011); http://dx.doi.org/10.1063/1.3623475 (3 pages) | Cited 1 time

Online Publication Date: 4 August 2011

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The pressure effect on the single-crystalline, nearly optimally doped high temperature cuprate superconductor YBa2Cu3O7-δ with a sharp ambient transition temperature of 90.7 K has been investigated resistively up to 29 GPa. An abrupt disappearance of superconductivity at 60 K under ∼24 GPa was detected, accompanied by a thermally activated resistance, suggesting a possible pressure-induced superconducting-semiconducting transition. By comparing the present results with those of recent high pressure work on Bi2Sr2Ca2Cu3O10-δ, it is proposed that the control of such electronic instabilities may further help raise the superconducting transition temperature record of 164 K in tri-layer cuprate superconductors by pressures.
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74.62.Fj Effects of pressure
74.72.-h Cuprate superconductors
74.25.F- Transport properties

High TC half-metallic fully-compensated ferrimagnetic Heusler compounds

I. Galanakis and E. Şaşıoğlu

Appl. Phys. Lett. 99, 052509 (2011); http://dx.doi.org/10.1063/1.3619844 (3 pages) | Cited 11 times

Online Publication Date: 4 August 2011

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Extensive ab-initio electronic structure calculations on Heusler alloys suggest that Cr2CoGa is the alloy of choice to achieve the half-metallic fully-compensated ferrimagnetism since (1) it has been already grown experimentally [T. Graf et al., Z. Anorg. Allg. Chem. 635, 976 (2009)], (2) half-metallic XA structure is favored energetically over all the studied lattice constant range with respect to the L21 which is not half-metallic, (3) the half-metallic gap is wide and the Fermi level falls at the middle of the gap and thus, it presents high degree of spin-polarization for a wide range of lattice constants, and (4) the Curie temperature is extremely high reaching the 1520 K.
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71.20.Gj Other metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics
61.66.Dk Alloys
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

High-power rf oscillation induced in half-metallic Co2MnSi layer by spin-transfer torque

R. Okura, Y. Sakuraba, T. Seki, K. Izumi, M. Mizuguchi, and K. Takanashi

Appl. Phys. Lett. 99, 052510 (2011); http://dx.doi.org/10.1063/1.3624470 (3 pages) | Cited 4 times

Online Publication Date: 4 August 2011

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The rf oscillation induced in a current-perpendicular-to-plane device with Co2MnSi (CMS) layers by spin-transfer torque was investigated to enhance the rf output power due to the large magnetoresistance (MR) ratio. A large MR ratio of 12.5% was obtained due to the large spin-polarization of CMS, and fundamental and second harmonic rf oscillations were clearly observed in the CMS layer. A high rf output power of 1.1 nW was achieved in spite of a small precession angle of 8.6°.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
84.30.Ng Oscillators, pulse generators, and function generators
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