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15 Oct 2012

Volume 101, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 161105 (2012); http://dx.doi.org/10.1063/1.4744947 (4 pages)

Nan Niu, Tsung-Li Liu, Igor Aharonovich, Kasey J. Russell, Alexander Woolf, Thomas C. Sadler, Haitham A. R. El-Ella, Menno J. Kappers, Rachel A. Oliver, and Evelyn L. Hu
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Electronic structure and optical band gap of CoFe2O4 thin films

A. V. Ravindra, P. Padhan, and W. Prellier

Appl. Phys. Lett. 101, 161902 (2012); http://dx.doi.org/10.1063/1.4759001 (4 pages) | Cited 1 time

Online Publication Date: 16 October 2012

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Electronic structure and optical band gap of CoFe2O4 thin films grown on (001) oriented LaAlO3 have been investigated. Surprisingly, these films show additional Raman modes at room temperature as compared to a bulk spinel structure. The splitting of Raman modes is explained by considering the short-range ordering of Co and Fe cations in octahedral site of spinel structure. In addition, an expansion of band-gap is observed with the reduction of film thickness, which is explained by the quantum size effect and misfit dislocation. Such results provide interesting insights for the growth of spinel phases.
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71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Influences of lattice vibration and electron transition on thermal emissivity of Nd3+ doped LaMgAl11O19 hexaaluminates for metallic thermal protection system

Hong-Zhi Liu, Zhan-Guo Liu, Jia-Hu Ouyang, and Ya-Ming Wang

Appl. Phys. Lett. 101, 161903 (2012); http://dx.doi.org/10.1063/1.4759006 (4 pages) | Cited 1 time

Online Publication Date: 16 October 2012

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Normal spectral emissivity of La1−xNdxMgAl11O19 (x = 0.05, 0.10, 0.15, 0.25) ceramics has a maximum value at the Nd3+ content of x = 0.10 in the wavelength range of 3–6 μm. The difference in emissivity at short wavelengths of 3–6 μm is tightly linked to the absorption transitions from 4I9/2 to 4F3/2, 4I15/2, and 4I13/2 and the intensities of radiation transitions from 4F3/2 to 4I11/2 and 4I13/2 of Nd3+ in LaMgAl11O19 ceramics. However, in the wavelength range of 6–14 μm, the emissivity is quite similar for all the samples, which can be ascribed to the stretching vibration of Al-O tetrahedron and Al-O octahedron.
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61.72.up Other materials
63.20.-e Phonons in crystal lattices
78.55.Hx Other solid inorganic materials
78.30.Hv Other nonmetallic inorganics

Atomic-scaled investigation of structure-dependent luminescence in Sialon:Ce phosphors

Fangfang Xu (许钫钫), Erwan Sourty, Xionghui Zeng (曾雄辉), Linlin Zhang (张琳琳), Lin Gan (甘霖), Xinliang Mou (牟新亮), Wei Shi (史 为), Yingchun Zhu (祝迎春), Fuqiang Huang (黄富 强), and Jingtai Zhao (赵景泰)

Appl. Phys. Lett. 101, 161904 (2012); http://dx.doi.org/10.1063/1.4759110 (5 pages) | Cited 1 time

Online Publication Date: 17 October 2012

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Here, we present direct correlation of luminescence properties to the atomic structures of Sialon:Ce phosphors. Luminescence of β-Sialon is revealed attributed to the intergrowth of a unit layer of α-Sialon:Ce-type structure on β-grain surfaces. The dense doping at fault sites either on the surface of or inside the α-Sialon crystallites might lead to intensified emission of light depending on the fault morphology. It seems that concentration quenching would not appear for Sialon:Ce phosphors unless high density of dislocations is created upon dense doping. Finally, structural evolution has been discussed aiming to greatly enhance the luminescence of Sialon phosphors.
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78.55.Hx Other solid inorganic materials
61.72.up Other materials
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Improvement of optical performance of ZnO/GaN p-n junctions with an InGaN interlayer

T. Wang, H. Wu, Z. Wang, C. Chen, and C. Liu

Appl. Phys. Lett. 101, 161905 (2012); http://dx.doi.org/10.1063/1.4760271 (4 pages) | Cited 1 time

Online Publication Date: 17 October 2012

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The ZnO films were deposited on GaN and with an interlayer of InGaN by atomic layer deposition. The orientation of the ZnO films was 〈0001〉 on InGaN, whereas it was 〈70math4〉 (perpendicular to (10math0) plane) on GaN. The lattice mismatch between ZnO and InGaN was about 0.3%, which is lower than that between ZnO and GaN (1.6%). With a lower lattice mismatch, the intensity of the near-band-edge emission increased about 120% and the full width at half maximum decreased 7.3 nm. Furthermore, ZnO/InGaN/GaN heterostructured light emitting diodes were fabricated. The electroluminescence spectra under forward bias showed a blue emission accompanied by a broad peak centered at 600 nm.
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85.60.Jb Light-emitting devices
68.55.ag Semiconductors
78.66.-w Optical properties of specific thin films
78.60.Fi Electroluminescence
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Voltage-assisted ion reduction in liquid crystal-silica nanoparticle dispersions

Shu-Wei Liao, Chia-Ting Hsieh, Chih-Chin Kuo, and Chi-Yen Huang

Appl. Phys. Lett. 101, 161906 (2012); http://dx.doi.org/10.1063/1.4760277 (4 pages) | Cited 1 time

Online Publication Date: 18 October 2012

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We demonstrate an effective method of reducing mobile ions in a silica nanoparticle (SN)-doped liquid crystal (LC) cell by alternating-current high-voltage pulse treatment (ACHVPT). In this method, the director distortion in LCs near the substrate creates a lifting force that moves the SNs toward the substrate. The moving SNs trap mobile ions in the cell bulk. After ACHVPT, the SNs and mobile ions are adsorbed onto the substrates, thereby significantly decreasing cell ion density. The ion density of the SN-doped LC cell after ACHVPT treatment is 1.5% of that of a pristine LC cell.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.70.-y Disperse systems; complex fluids

Branched carbon nanotube reinforcements for improved strength of polyethylene nanocomposites

Ling Liu, Lin Zhang, and Jim Lua

Appl. Phys. Lett. 101, 161907 (2012); http://dx.doi.org/10.1063/1.4761936 (5 pages) | Cited 1 time

Online Publication Date: 19 October 2012

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A bio-inspired design of polyethylene nanocomposites is presented in this letter using branched carbon nanotubes (BCNTs) as reinforcements. Using coarse-grained molecular dynamics simulations, we demonstrate that the pullout strength of the proposed BCNT nanofibers can be an order of magnitude higher than that of CNT reinforcements. The drastically improved interfacial shearing strength is found to be strongly dependent on the geometry of nanofibers, the molecular weight of matrix polymers, and the pullout velocity. By analyzing the time-evolving molecular configurations of BCNT nanofibers and surrounding polymer chains, the underlying strengthening mechanisms are discussed and strategies for further improvement are suggested.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
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Scalable control of terahertz radiation from ultrashort laser-gas interaction

Min Chen, Xiao-Hui Yuan, and Zheng-Ming Sheng

Appl. Phys. Lett. 101, 161908 (2012); http://dx.doi.org/10.1063/1.4761941 (4 pages) | Cited 1 time

Online Publication Date: 19 October 2012

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Terahertz radiation from ultrashort laser pulse interaction with a neutral gas target via ionization induced transverse currents is studied analytically and by particle-in-cell simulations. It is shown that the radiation amplitude and temporal shape depend not only on the driving laser parameters but also on the target parameters both for the forward and backward emissions. For given laser parameters, simply by tuning the gas length and the concentration of the effective ionized electrons, the terahertz temporal shape can be changed in scale with the gas length while keeping the radiation amplitude unchanged. This provides an easy way for terahertz radiation control for applications.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.-v Laser optical systems: design and operation
78.70.Gq Microwave and radio-frequency interactions
42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems

Internal friction and dynamic modulus in Ru-50Nb ultra-high temperature shape memory alloys

L. Dirand, M. L. Nó, K. Chastaing, A. Denquin, and J. San Juan

Appl. Phys. Lett. 101, 161909 (2012); http://dx.doi.org/10.1063/1.4761475 (4 pages) | Cited 1 time

Online Publication Date: 19 October 2012

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The martensitic transformations in ultra-high temperature Ru-50Nb shape memory alloys have been studied by internal friction and dynamic modulus measurements. Two successive transformations from the high temperature cubic β phase to a tetragonal β′ martensite and then to another monoclinic β″ martensite have been found. Both transformations exhibit a sharp internal friction peak and a clear softening of the dynamic modulus, being a signature of the thermo-elastic martensitic transformations. In addition, a pseudo relaxation peak strongly dependent on time has been found and analyzed, concluding that it is linked to a pinning effect of martensite interfaces by point defects.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
64.70.kd Metals and alloys
81.30.Kf Martensitic transformations
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Hole transport in boron delta-doped diamond structures

G. Chicot, T. N. Tran Thi, A. Fiori, F. Jomard, E. Gheeraert, E. Bustarret, and J. Pernot

Appl. Phys. Lett. 101, 162101 (2012); http://dx.doi.org/10.1063/1.4758994 (4 pages) | Cited 1 time

Online Publication Date: 15 October 2012

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The temperature dependence of the hole sheet density and mobility of four capped delta boron doped [100]-oriented epilayers has been investigated experimentally and theoretically over a large temperature range (6 K<T<500 K). The influence of the parallel conduction through the thick buffer layer overgrown on the diamond substrate was shown not to be negligible near room temperature. This could lead to erroneous estimates of the hole mobility in the delta layer. None of the delta-layers studied showed any quantum confinement enhancement of the mobility, even the one which was thinner than 2 nm.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.72.up Other materials
68.55.ag Semiconductors
73.61.Cw Elemental semiconductors

Dependence of radiative efficiency and deep level defect incorporation on threading dislocation density for InGaN/GaN light emitting diodes

A. Armstrong, T. A. Henry, D. D. Koleske, M. H. Crawford, K. R. Westlake, and S. R. Lee

Appl. Phys. Lett. 101, 162102 (2012); http://dx.doi.org/10.1063/1.4759003 (4 pages) | Cited 1 time

Online Publication Date: 16 October 2012

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The influence of threading dislocation (TD) density on electroluminescence and deep level defect incorporation in the multi-quantum well regions of InGaN/GaN light emitting diodes (LEDs) was investigated. LED efficiency increased with decreasing TD density. To elucidate the impact of TD density on deep level defect incorporation and resulting radiative efficiency, deep level optical spectroscopy and lighted capacitance voltage measurements were applied to the LEDs. Interestingly, the concentration of all observed deep levels decreased with TD density reduction, but their concentration also varied strongly with depth in the multi-quantum well region. These trends indicate that (1) TDs strongly influence point defect incorporation in InGaN/GaN LEDs and (2) TDs, possibly in conjunction with point defects, are detrimental to LED efficiency.
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85.60.Jb Light-emitting devices

Role of the Ge surface during the end of range dissolution

S. Boninelli, G. Impellizzeri, A. Alberti, F. Priolo, F. Cristiano, and C. Spinella

Appl. Phys. Lett. 101, 162103 (2012); http://dx.doi.org/10.1063/1.4759031 (4 pages) | Cited 1 time

Online Publication Date: 16 October 2012

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We investigated the structure of end-of-range (EOR) defects in Ge and the role played by the surface during their dissolution caused by annealing. Ge samples were amorphized with Ge+ ions at two different energies (30 and 100 keV) in order to induce, after solid phase epitaxial regrowth, the formation of EOR band at different depths. High resolution x-ray diffraction and transmission electron microscopy showed that the EOR population consists mainly on small defects and few dislocation loops lying on 〈001〉 planes. The deepest EOR defects are more stable during thermal annealing demonstrating the role of the surface during their dissolution.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
65.40.gp Surface energy
81.05.Cy Elemental semiconductors

Topological insulator Bi2Te3 films synthesized by metal organic chemical vapor deposition

Helin Cao, Rama Venkatasubramanian, Chang Liu, Jonathan Pierce, Haoran Yang, M. Zahid Hasan, Yue Wu, and Yong P. Chen

Appl. Phys. Lett. 101, 162104 (2012); http://dx.doi.org/10.1063/1.4760226 (4 pages) | Cited 2 times

Online Publication Date: 17 October 2012

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Topological insulator (TI) materials such as Bi2Te3 and Bi2Se3 have attracted strong recent interests. Large scale, high quality TI thin films are important for developing TI-based device applications. In this work, structural and electronic properties of Bi2Te3 thin films deposited by metal organic chemical vapor deposition (MOCVD) on GaAs (001) substrates were characterized via x-ray diffraction (XRD), Raman spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and electronic transport measurements. The characteristic topological surface states with a single Dirac cone have been clearly revealed in the electronic band structure measured by ARPES, confirming the TI nature of the MOCVD Bi2Te3 films. Resistivity and Hall effect measurements have demonstrated relatively high bulk carrier mobility of ∼350 cm2/Vs at 300 K and ∼7400 cm2/Vs at 15 K. We have also measured the Seebeck coefficient of the films. Our demonstration of high quality topological insulator films grown by a simple and scalable method is of interests for both fundamental research and practical applications of thermoelectric and TI materials.
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68.55.ag Semiconductors
73.61.Le Other inorganic semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.33.Ya Chemistry of MOCVD and other vapor deposition methods
72.20.Pa Thermoelectric and thermomagnetic effects
72.20.My Galvanomagnetic and other magnetotransport effects

Microscopic characteristics of dynamic nuclear polarization and selective nuclear depolarization at the ν = 2/3 spin phase transition

M. H. Fauzi, S. Watanabe, and Y. Hirayama

Appl. Phys. Lett. 101, 162105 (2012); http://dx.doi.org/10.1063/1.4761955 (3 pages)

Online Publication Date: 19 October 2012

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The ability to manipulate the nuclear spin degree of freedom in semiconductor quantum structures is necessary for development of nuclear spintronics based on solid-state systems. Here, we developed a method to selectively depolarize the nuclear spin, the 〈+Iz〉 or the 〈−Iz〉 component, residing in a GaAs quantum well specimen after dynamic nuclear polarization by applying radio frequency pulse to either spin-unpolarized or spin-polarized nuclear magnetic resonance lines obtained at the spin transition of the filling ν = 2/3. Our results are evidence that the spin-unpolarized (spin-polarized) domain mediates the 〈+Iz〉 (〈−Iz〉) nuclear spin polarization.
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76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization
73.43.Nq Quantum phase transitions
76.60.-k Nuclear magnetic resonance and relaxation
72.25.Dc Spin polarized transport in semiconductors
73.63.Hs Quantum wells

Temperature-dependent properties of semimetal graphite-ZnO Schottky diodes

R. Yatskiv and J. Grym

Appl. Phys. Lett. 101, 162106 (2012); http://dx.doi.org/10.1063/1.4761958 (3 pages) | Cited 2 times

Online Publication Date: 19 October 2012

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Highly rectifying semimetal graphite/ZnO Schottky diodes with a low-ideality-factor (1.08 at 300 K) were investigated by temperature-dependent current-voltage measurements. The current transport was dominated by thermionic emission between 300 and 420 K and the extracted barrier height followed the Schottky-Mott relation. A Richardson constant (A** = 0.272 A cm−2K−2) extracted from the Richardson plot shows nearly linear characteristics in the temperature range 300–420 K.
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85.30.Kk Junction diodes
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Formation of nanoscale magnetic bubbles in ferromagnetic insulating manganite La7/8Sr1/8MnO3

T. Nagai, M. Nagao, K. Kurashima, T. Asaka, W. Zhang, and K. Kimoto

Appl. Phys. Lett. 101, 162401 (2012); http://dx.doi.org/10.1063/1.4760266 (5 pages)

Online Publication Date: 15 October 2012

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We have observed the response of spin arrangements to external magnetic fields in a multiorbital Mott insulator, ferromagnetic insulating manganite La7/8Sr1/8MnO3, by low-temperature in situ Lorentz microscopy. Magnetic fields normal to the plane of the thin-plate sample continuously change the width of domains in the serpentine-like domain structure, eventually giving rise to nanoscale elliptical magnetic bubbles of ∼200 nm major diameter at 3.6 kOe. The formation of these bubbles implies large magnetic anisotropy related to the orbital ordering and suggests the possibility of manipulating the bubbles using an electric field.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.Fk Domain structures in nanoparticles
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Gw Magnetic anisotropy

Spatially resolving variations in giant magnetoresistance, undetectable with four-point probe measurements, using infrared microspectroscopy

C. S. Kelley, S. M. Thompson, M. D. Illman, S. LeFrançois, and P. Dumas

Appl. Phys. Lett. 101, 162402 (2012); http://dx.doi.org/10.1063/1.4760282 (4 pages)

Online Publication Date: 16 October 2012

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Magnetorefractive infrared (IR) microspectroscopy is demonstrated to resolve spatial variations in giant magnetoresistance (GMR) and, by modelling, provide an insight into the origin of the variations. Spatial variations are shown to be masked in conventional four-point probe electrical or IR spectral measurements. IR microspectroscopy was performed at the SMIS beamline at the SOLEIL synchrotron, modified to enable measurements in magnetic fields. A GMR gradient was induced in a CoFe/Cu multilayer sample by annealing in a temperature gradient. Modelling revealed that variations in GMR at 900 Oe could be attributed to local variations in interlayer coupling locally changing the switching field.
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81.05.Bx Metals, semimetals, and alloys
81.40.Gh Other heat and thermomechanical treatments
78.30.Er Solid metals and alloys
78.20.Ls Magneto-optical effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance

Room temperature ferromagnetic behavior in cluster free, Co doped Y2O3 dilute magnetic oxide films

C. N. Wu, S. Y. Huang, W. C. Lee, Y. H. Chang, T. S. Wu, Y. L. Soo, M. Hong, and J. Kwo

Appl. Phys. Lett. 101, 162403 (2012); http://dx.doi.org/10.1063/1.4760284 (5 pages) | Cited 1 time

Online Publication Date: 16 October 2012

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Extensive structural analysis and magnetic properties are reported on cluster free, dilute magnetic oxide of Co doped Y2O3 (Co:Y2O3) film by low temperature deposition and characterized by extended x-ray absorption fine structure, x-ray absorption near edge structure, magnetometer, and x-ray magnetic circular dichroism. Room temperature ferromagnetism was observed, and the saturation magnetic moment was modulated by oxygen vacancy concentration through post annealing process. Oxygen vacancies are shown to play a crucial role in ferromagnetic ordering, as defect centers in the bound magnetic polaron model to account for this dilute magnetic oxide of medium band gap with low carrier concentration.
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75.70.Ak Magnetic properties of monolayers and thin films
78.70.Dm X-ray absorption spectra
78.20.Ls Magneto-optical effects
75.30.Cr Saturation moments and magnetic susceptibilities
71.38.-k Polarons and electron-phonon interactions
73.61.Ng Insulators

Parallel-leaky capacitance equivalent circuit model for MgO magnetic tunnel junctions

Ajeesh M. Sahadevan, Kalon Gopinadhan, Charanjit S. Bhatia, and Hyunsoo Yang

Appl. Phys. Lett. 101, 162404 (2012); http://dx.doi.org/10.1063/1.4760279 (5 pages)

Online Publication Date: 17 October 2012

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The capacitance of MgO based magnetic tunnel junctions (MTJs) has been observed to be magnetic field dependent. We propose an equivalent circuit for the MTJs with a parallel-leaky capacitance (Cl) across the series combination of geometric and interfacial capacitance. The analysis of junctions with different tunneling magnetoresistance (TMR) values suggests higher Cl for low TMR junctions. Using Cole-Cole plots, the capacitive nature of MTJs is manifested. Fitting with Maxwell-Wagner capacitance model validates the RC parallel network model for MTJs and the extracted field dependent parameters match with the experimental values.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.20.My Galvanomagnetic and other magnetotransport effects

Metastable state in a shape-anisotropic single-domain nanomagnet subjected to spin-transfer-torque

Kuntal Roy, Supriyo Bandyopadhyay, and Jayasimha Atulasimha

Appl. Phys. Lett. 101, 162405 (2012); http://dx.doi.org/10.1063/1.4761250 (4 pages)

Online Publication Date: 17 October 2012

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We predict the existence of a metastable magnetization state in a single-domain nanomagnet with uniaxial shape anisotropy. It emerges when a spin-polarized current, which delivers a spin-transfer-torque possessing a field-like component, is injected into the nanomagnet. At a metastable state, the internal torque due to nanomagnet's shape anisotropy cancels the externally applied spin-transfer-torque and hence the net torque acting on the magnetization becomes zero. Therefore, it prevents spin-transfer-torque from switching the magnetization from one stable state along the easy axis to the other, even in the presence of room-temperature thermal fluctuations.
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75.30.Gw Magnetic anisotropy
75.78.Jp Ultrafast magnetization dynamics and switching
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.Fk Domain structures in nanoparticles

Magnetocaloric properties of La(Fe,Si)13-based material and its hydride prepared by industrial mischmetal

L. F. Bao, F. X. Hu, L. Chen, J. Wang, J. R. Sun, and B. G. Shen

Appl. Phys. Lett. 101, 162406 (2012); http://dx.doi.org/10.1063/1.4760262 (5 pages)

Online Publication Date: 18 October 2012

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Here, we choose La-Ce-Pr-Nd industrial mischmetal with low purity as raw material to prepare La(Fe,Si)13-based magnetocaloric material and its hydride. It is demonstrated that the introduced impurities in the starting materials do not impair the formation of NaZn13-type structure. The multi-replacement of La by magnetic atoms Ce,Pr,Nd enhances Curie temperature TC while keeps the strong itinerant electron metamagnetic behavior. As a result, good magnetocaloric (MCE) properties appear in La0.7(Ce,Pr,Nd)0.3Fe11.6Si1.4 (LRFS) compound. The incorporation of interstitial H atom remarkably reduces hysteresis loss while increases TC to 314 K. The effective refrigeration capacity after deducting hysteresis can be increased by ∼128% upon H doping.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Hx Magnetic impurity interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.up Other materials
61.72.jj Interstitials

Dynamic spin injection into chemical vapor deposited graphene

A. K. Patra, S. Singh, B. Barin, Y. Lee, J.-H. Ahn, E. del Barco, E. R. Mucciolo, and B. Özyilmaz

Appl. Phys. Lett. 101, 162407 (2012); http://dx.doi.org/10.1063/1.4761932 (4 pages) | Cited 2 times

Online Publication Date: 19 October 2012

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We demonstrate dynamic spin injection into chemical vapor deposition (CVD) grown graphene by spin pumping from permalloy (Py) layers. Ferromagnetic resonance measurements at room temperature reveal a strong enhancement of the Gilbert damping at the Py/graphene interface, indeed exceeding that observed in Py/platinum interfaces. Similar results are also shown on Co/graphene layers. This enhancement in the Gilbert damping is understood as the consequence of spin pumping at the interface driven by magnetization dynamics. Our observations suggest a strong enhancement of spin-orbit coupling in CVD graphene, in agreement with earlier spin valve measurements.
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72.25.Mk Spin transport through interfaces
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Light-induced magnetization reversal of high-anisotropy TbCo alloy films

Sabine Alebrand, Matthias Gottwald, Michel Hehn, Daniel Steil, Mirko Cinchetti, Daniel Lacour, Eric E. Fullerton, Martin Aeschlimann, and Stéphane Mangin

Appl. Phys. Lett. 101, 162408 (2012); http://dx.doi.org/10.1063/1.4759109 (4 pages) | Cited 1 time

Online Publication Date: 19 October 2012

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Magnetization reversal using circularly polarized light provides a way to control magnetization without any external magnetic field and has the potential to revolutionize magnetic data storage. However, in order to reach ultra-high density data storage, high anisotropy media providing thermal stability are needed. Here, we evidence all-optical magnetization switching for different TbxCo1−x ferrimagnetic alloy compositions using fs- and ps-laser pulses and demonstrate all-optical switching for films with anisotropy fields reaching 6 T corresponding to anisotropy constants of 3 × 106 ergs/cm3. Optical magnetization switching is observed only for alloy compositions where the compensation temperature can be reached through sample heating.
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75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
81.40.Gh Other heat and thermomechanical treatments
78.66.Bz Metals and metallic alloys
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An ultra-fast superconducting Nb nanowire single-photon detector for soft x-rays

K. Inderbitzin, A. Engel, A. Schilling, K. Il'in, and M. Siegel

Appl. Phys. Lett. 101, 162601 (2012); http://dx.doi.org/10.1063/1.4759046 (5 pages)

Online Publication Date: 15 October 2012

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Although superconducting nanowire single-photon detectors (SNSPDs) are well studied regarding the detection of infrared/optical photons and keV-molecules, no studies on continuous x-ray photon counting by thick-film detectors have been reported so far. We fabricated a 100 nm thick niobium x-ray SNSPD (an X-SNSPD) and studied its detection capability of photons with keV-energies in continuous mode. The detector is capable to detect photons even at reduced bias currents of 0.4%, which is in sharp contrast to optical thin-film SNSPDs. No dark counts were recorded in extended measurement periods. Strikingly, the signal amplitude distribution depends significantly on the photon energy spectrum.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.60.Gz Photodetectors (including infrared and CCD detectors)

Superconducting epitaxial thin films of CeNixBi2 with a bismuth square net structure

Alexander Buckow, Katharina Kupka, Reiner Retzlaff, Jose Kurian, and Lambert Alff

Appl. Phys. Lett. 101, 162602 (2012); http://dx.doi.org/10.1063/1.4760264 (4 pages) | Cited 1 time

Online Publication Date: 18 October 2012

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We have grown highly epitaxial and phase pure thin films of the arsenic-free pnictide compound CeNixBi2 on (100) MgO substrates by reactive molecular beam epitaxy (RMBE). X-ray diffraction and reflection high-energy electron diffraction of the films confirm the ZrCuSiAs structure with a Bi square net layer. Superconductivity was observed in magnetization and resistivity measurements for x = 0.75 to 0.93 in these CeNixBi2 thin films with the highest critical temperature of 4.05 K and a resistive transition width of 0.1 K for x = 0.86. Our results indicate that thin film deposition by RMBE provides a tool to synthesize high-quality pnictide superconductors of the novel 112 type.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Ha Magnetic properties including vortex structures and related phenomena
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
74.25.F- Transport properties
74.70.Xa Pnictides and chalcogenides

Observation of partial Meissner effect and flux pinning in superconducting lead containing non-superconducting parts

W. Treimer, O. Ebrahimi, and N. Karakas

Appl. Phys. Lett. 101, 162603 (2012); http://dx.doi.org/10.1063/1.4762860 (4 pages)

Online Publication Date: 19 October 2012

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Partially suppressed Meissner effect and magnetic flux trapping in the bulk of poly-crystalline Pb samples with virtually zero demagnetization and large (cm3) volume containing non-superconducting parts could be visualized by polarized neutrons and quantified with respect to the shape and amount of the trapped flux in the intermediate state of lead. These measurements provided a unique look at the macroscopic Quantum mechanics effects and the coexistence of superconducting state, intermediate state, and normal conducting parts in the same sample, respectively.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Wx Vortex pinning (includes mechanisms and flux creep)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
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