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26 Sep 2011

Volume 99, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 131101 (2011); http://dx.doi.org/10.1063/1.3641907 (3 pages)

Linas Minkevičius, Vincas Tamošiūnas, Irmantas Kašalynas, Dalius Seliuta, Gintaras Valušis, Alvydas Lisauskas, Sebastian Boppel, Hartmut G. Roskos, and Klaus Köhler
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Controlled positions and kinetic analysis of spontaneous tin whisker growth

Chien-Hao Su, Hao Chen, Hsin-Yi Lee, and Albert T. Wu

Appl. Phys. Lett. 99, 131906 (2011); http://dx.doi.org/10.1063/1.3643472 (3 pages)

Online Publication Date: 28 September 2011

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This study achieved controlling the positions of spontaneous growth of tin whiskers. We surmounted the unpredictable growing nature of such whiskers and performed accurately quantitative analyses of the growth kinetics and yielded precise measurement of the growth rate. Furthermore, using synchrotron radiation x-ray, this study determined the stress variations in conjunction with whisker growth that fitted appropriately to the model. Accordingly, the results could address the debate held for decades and prove that forming a surface oxide layer is one of the required and necessary conditions for controlling the positions of spontaneous growth of tin whiskers.
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68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
82.20.Pm Rate constants, reaction cross sections, and activation energies
07.85.Qe Synchrotron radiation instrumentation

A thermochromic low-emittance coating: Calculations for nanocomposites of In2O3:Sn and VO2

S.-Y. Li, G. A. Niklasson, and C. G. Granqvist

Appl. Phys. Lett. 99, 131907 (2011); http://dx.doi.org/10.1063/1.3641869 (3 pages) | Cited 3 times

Online Publication Date: 28 September 2011

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Calculations based on the Bruggeman effective medium theory were applied to thin films comprising a heavily doped wide band gap semiconductor (specifically In2O3:Sn (ITO)) and VO2. Films with ∼20 vol. % of VO2 can combine a 10% thermochromic modulation of the solar energy throughput with a luminous transmittance of 50%–60% and low thermal emittance. The maximum thermochromic modulation is ∼13% and occurs at ∼35 vol. % VO2. Coatings of ITO-VO2 are of interest for energy efficient fenestration.
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68.55.ag Semiconductors
78.20.nb Photothermal effects
78.66.Li Other semiconductors
78.67.Sc Nanoaggregates; nanocomposites

Photoluminescence due to inelastic exciton-exciton scattering in ZnMgO-alloy thin film

C. H. Chia, J. N. Chen, and Y. M. Hu

Appl. Phys. Lett. 99, 131908 (2011); http://dx.doi.org/10.1063/1.3646116 (3 pages) | Cited 1 time

Online Publication Date: 28 September 2011

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We studied the photoluminescence of ZnMgO thin film, grown by the radiofrequency sputtering method, as a function of excitation intensity and temperature. As the excitation intensity increases, a nonlinear emission band caused by the radiative recombination of the inelastic exciton-exciton scattering was detected at low temperature. We found that the inelastic exciton-exciton scattering process can only persist up to T ∼ 260 K. The nonlinear emission band observed at room temperature is due to the radiative recombination of the electron-hole plasma.
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78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Evidence of lattice tilt and slip in m-plane InGaN/GaN heterostructure

Shunji Yoshida, Toshiya Yokogawa, Yasuhiko Imai, Shigeru Kimura, and Osami Sakata

Appl. Phys. Lett. 99, 131909 (2011); http://dx.doi.org/10.1063/1.3644978 (3 pages) | Cited 10 times

Online Publication Date: 29 September 2011

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Using high-resolution microbeam x-ray diffraction and cross-section transmission electron microscopy, we investigated in-plane anisotropy resulting from epilayer lattice tilts in heteroepitaxial InGaN on a m-plane GaN substrate. The in-plane structure consists of two lattice tilts along the [11math0] direction corresponding to (10math0) and (0math10) slip planes inclined at roughly 60° from the m-plane. Based on the Peierls-Nabarro model, we explain this structure by proposing a slip system via the {10math0} prism plane with 〈11math0〉-type slip directions.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Mm Grain and twin boundaries
68.55.ag Semiconductors
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

The curious case of thin-body Ge crystallization

R. Duffy, M. Shayesteh, B. McCarthy, A. Blake, M. White, J. Scully, R. Yu, A.-M. Kelleher, M. Schmidt, N. Petkov, L. Pelaz, and L. A. Marqués

Appl. Phys. Lett. 99, 131910 (2011); http://dx.doi.org/10.1063/1.3643160 (3 pages) | Cited 2 times

Online Publication Date: 29 September 2011

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The authors investigate the templated crystallization of thin-body Ge fin structures with high aspect ratios. Experimental variables include fin thickness and thermal treatments, with fin structures oriented in the 〈110〉 direction. Transmission electron microscopy determined that various crystal defects form during crystallization of amorphous Ge regions, most notably {111} stacking faults, twin boundaries, and small crystallites. In all cases, the nature of the defects is dependent on the fin thickness and thermal treatments applied. Using a standard 600 °C rapid-thermal-anneal, Ge structures with high aspect ratios crystallize with better crystal quality and fewer uncured defects than the equivalent Si case, which is a cause for optimism for thin-film Ge devices.
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64.70.kg Semiconductors
61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects

Buckling of poly(methyl methacrylate) in stimulus-responsive shape recovery

Yong Zhao, Chang Chun Wang, Wei Min Huang, and Hendra Purnawali

Appl. Phys. Lett. 99, 131911 (2011); http://dx.doi.org/10.1063/1.3645005 (3 pages) | Cited 2 times

Online Publication Date: 30 September 2011

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We investigate buckling phenomenon during shape recovery in a poly(methyl methacrylate) upon immersing in ethanol (chemo-responsive) and heating (thermo-responsive). The underlying mechanism is revealed and the influential factors are discussed. Such buckling phenomenon is generic and applicable to all materials during shape recovery when certain conditions (as discussed here) are satisfied.
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81.40.Lm Deformation, plasticity, and creep
62.20.mq Buckling
61.41.+e Polymers, elastomers, and plastics

Dynamic mechanical behavior of magnetorheological nanocomposites filled with carbon nanotubes

R. Li and L. Z. Sun

Appl. Phys. Lett. 99, 131912 (2011); http://dx.doi.org/10.1063/1.3645627 (3 pages) | Cited 1 time

Online Publication Date: 30 September 2011

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Magnetorheological (MR) elastomer composites with the addition of multi-walled carbon nanotubes are developed. The dynamic mechanical responses of the MR nanocomposites to applied magnetic fields are investigated through dynamic mechanical analysis. It is found that a small amount of carbon nanotubes can effectively improve the mechanical performance of conventional MR elastomers. The MR nanocomposites have shown not only large jumps in zero-field dynamic stiffness and damping, but also higher magnetic-field-induced improvement in these dynamic mechanical properties.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
75.75.-c Magnetic properties of nanostructures
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
62.23.Pq Composites (nanosystems embedded in a larger structure)

Multi-beam generations at pre-designed directions based on anisotropic zero-index metamaterials

Qiang Cheng, Wei Xiang Jiang, and Tie Jun Cui

Appl. Phys. Lett. 99, 131913 (2011); http://dx.doi.org/10.1063/1.3645628 (3 pages) | Cited 7 times

Online Publication Date: 30 September 2011

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We show that anisotropic zero-index metamaterials (AZIMs) can be utilized to realize single- and multiple-beam generations in the pre-designed directions. It has been shown that a high-gain beam will be generated when a line source is located in an AZIM, directing to the AZIM principle-axis direction. By rotating the principle axis to an arbitrary angle, the beam direction is adjusted correspondingly to that angle. Therefore, multi-beams are generated at the desired directions by designing differently oriented AZIMs. An experiment is carried out to validate this property, which shows good agreement to the theoretical analysis.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media

Diffusion behavior of dual capping layers in TiN/LaN/AlN/HfSiOx/Si stack

X. H. Zheng, A. P. Huang, Z. S. Xiao, M. Wang, X. Y. Liu, Z. W. Wu, and Paul K. Chu

Appl. Phys. Lett. 99, 131914 (2011); http://dx.doi.org/10.1063/1.3643517 (3 pages) | Cited 1 time

Online Publication Date: 30 September 2011

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The diffusion behavior and interlayer interactions in the LaN/AlN dual capping layers of TiN/LaN/AlN/HfSiOx/Si stacks are investigated. Depth profiling and chemical state analysis performed after partial removal of the TiN gate indicate that Al-O replaces Al-N forming an Al-O dipole layer between the TiN and high-k layer after annealing. Meanwhile, La diffuses into HfSiOx and the La-based dipole is controlled by suppression of O diffusion to the bottom layer. Our results reveal that the properties of the TiN/LaN/AlN/HfSiOx/Si stack can be improved significantly by the dual capping layers.
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66.30.Ny Chemical interdiffusion; diffusion barriers
81.40.Gh Other heat and thermomechanical treatments
77.55.df For silicon electronics
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

InAs quantum dots and quantum wells grown on stacking-fault controlled InP nanowires with wurtzite crystal structure

Kenichi Kawaguchi, Magnus Heurlin, David Lindgren, Magnus T. Borgström, Martin Ek, and Lars Samuelson

Appl. Phys. Lett. 99, 131915 (2011); http://dx.doi.org/10.1063/1.3646386 (3 pages) | Cited 2 times

Online Publication Date: 30 September 2011

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Heteroepitaxial growth of InAs was investigated on sidewalls of InP nanowires (NWs) using metal-organic vapor phase epitaxy. InAs quantum wells (QWs) with smooth surface were formed on the InP NWs having perfect wurtzite phase structure. On the other hand, InAs quantum dots (QDs) were formed on wurtzite InP NWs purposely introduced with stacking-fault segments. Photoluminescence from single NWs attributed to both QWs and QDs was observed.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.Ta Quantum dots
81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
81.15.Kk Vapor phase epitaxy; growth from vapor phase
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Inelastic electron tunneling spectroscopy of HfO2 gate stacks: A study based on first-principles modeling

E. Scalise, M. Houssa, G. Pourtois, V. V. Afanas’ev, and A. Stesmans

Appl. Phys. Lett. 99, 132101 (2011); http://dx.doi.org/10.1063/1.3644158 (3 pages)

Online Publication Date: 26 September 2011

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A first-principles modeling approach is used to investigate the vibrational properties of HfO2. The calculated phonon density of states is compared to experimental results obtained from inelastic electron tunneling spectroscopy (IETS) of various metal-oxide-semiconductor devices with HfO2 gate stacks. This comparison provides deep insights into the nature of the signatures of the complicated IETS spectra and provides valuable structural information about the gate stack, such as the possible presence of oxygen vacancies in jet-vapour deposited HfO2. Important structural differences between the interface of atomic-layer or molecular-beam deposited HfO2 and the Si substrate are also revealed.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
73.20.At Surface states, band structure, electron density of states

Surface barrier height lowering at above 540 K in AlInN/AlN/GaN heterostructures

Md. Tanvir Hasan, Hirokuni Tokuda, and Masaaki Kuzuhara

Appl. Phys. Lett. 99, 132102 (2011); http://dx.doi.org/10.1063/1.3644161 (3 pages)

Online Publication Date: 28 September 2011

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Hall mobility (μH) and two dimensional electron gas density (ns) have been measured from 77 up to 973 K in AlInN/AlN/GaN heterostructures, where the atmospheric condition is changed as measured in vacuum and air. The μH decreases monotonically with increasing the temperature. The characteristic feature is observed in ns that it is almost constant up to around 540 K and shows sudden increase at higher temperatures when measured in the vacuum, while it is almost constant measured in the air. The surface barrier lowering originated from the decomposition of the surface oxide layer on AlInN is proposed as the most probable mechanism for the increase in ns.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects

Enhancement of magnetoresistance by ultra-thin Zn wüstite layer

Yoshihiko Fuji, Michiko Hara, Hiromi Yuasa, Shuichi Murakami, and Hideaki Fukuzawa

Appl. Phys. Lett. 99, 132103 (2011); http://dx.doi.org/10.1063/1.3644470 (3 pages)

Online Publication Date: 29 September 2011

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We have investigated a hybrid magnetic material composed of ultra-thin oxide spin-filtering layer/ferromagnetic layer (FML) for magnetoresistance (MR) enhancement. Using Zn-Fe oxide/Fe50Co50 as a free layer in current-perpendicular-to-plane giant magnetoresistive films, the MR ratio and ΔRA (the change of resistance area product) were enhanced to 26.0% and 52 mΩ μm2 at a small RA (resistance area product) of about 0.2 Ω μm2, respectively. Structural analysis revealed that the Zn wüstite structure is responsible for the enhancement of the MR ratio, and spin-polarization of wüstite/FML is higher than that of spinel ferrite/FML.
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75.47.De Giant magnetoresistance
75.50.Bb Fe and its alloys
75.50.Gg Ferrimagnetics
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
72.15.Gd Galvanomagnetic and other magnetotransport effects

Investigating the improvement of resistive switching trends after post-forming negative bias stress treatment

Hsueh-Chih Tseng, Ting-Chang Chang, Jheng-Jie Huang, Po-Chun Yang, Yu-Ting Chen, Fu-Yen Jian, S. M. Sze, and Ming-Jinn Tsai

Appl. Phys. Lett. 99, 132104 (2011); http://dx.doi.org/10.1063/1.3645004 (3 pages) | Cited 5 times

Online Publication Date: 29 September 2011

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This paper investigates the improvement of resistive switching trends after post-forming negative bias stress treatment of a Pt/Yb2O3/TiN device that has undergone positive bias forming process for activation. After the treatment, characteristics of the conductive filament, such as the temperature dependence of resistivity and transition mechanism, undergo changes. Furthermore, this treatment causes the conductive filament to transform from being primarily composed of vacancies to being metallic Yb dominant, which not only reduces operation voltages such as Vset and Vreset but also improves the on/off ratio. In reliability tests, the device has stable retention.
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84.30.Sk Pulse and digital circuits

Charge transport in hierarchical α-Fe2O3 nanostructures

K. R. G. Karthik, H. K. Mulmudi, K. B. Jinesh, N. Mathews, C. H. Sow, Y. Z. Huang, and S. G. Mhaisalkar

Appl. Phys. Lett. 99, 132105 (2011); http://dx.doi.org/10.1063/1.3641903 (3 pages) | Cited 2 times

Online Publication Date: 30 September 2011

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Electronic properties of individual polycrystalline α-Fe2O3 nanojunctions have been evaluated. By measuring the space charge limited current, the electron mobilities of the nanorods and nanojunctions were estimated. The mobility of the individual nanojunctions was found to be significantly lower than the individual nanorods. The trend clearly associates with the presence of junctions and grain boundaries in the nanorods. Impedance spectroscopy analysis of individual nanojunctions has been carried out to distinguish between the effects of the grain boundaries and the nanojunctions.
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73.63.Bd Nanocrystalline materials
77.22.Jp Dielectric breakdown and space-charge effects
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance
61.72.Mm Grain and twin boundaries
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
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Magnetic anisotropy of FePt: Effect of lattice distortion and chemical disorder

C. J. Aas, L. Szunyogh, J. S. Chen, and R. W. Chantrell

Appl. Phys. Lett. 99, 132501 (2011); http://dx.doi.org/10.1063/1.3644478 (3 pages) | Cited 2 times

Online Publication Date: 26 September 2011

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We perform first principles calculations of the magnetocrystalline anisotropy energy (MAE) in the five samples of L10 FePt that were studied experimentally by Ding and co-workers [J. Appl. Phys. 97, 10H303 (2005)]. The effect of temperature-induced spin fluctuations is estimated by scaling the MAE down according to previous Langevin dynamics simulations. Including chemical disorder as given in experiment, the experimental correlation between the MAE and the lattice mismatch is qualitatively well reproduced. Moreover, we determine the chemical order parameters that reproduce exactly the experimental MAE of each of the samples. Our observations lead to the conclusion that the MAE of the FePt samples is determined by the chemical disorder rather than by lattice distortion.
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75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.30.Ds Spin waves

Spin-transfer-torque reversal in perpendicular anisotropy spin valves with composite free layers

I. Yulaev, M. V. Lubarda, S. Mangin, V. Lomakin, and Eric E. Fullerton

Appl. Phys. Lett. 99, 132502 (2011); http://dx.doi.org/10.1063/1.3643046 (3 pages) | Cited 5 times

Online Publication Date: 26 September 2011

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We describe modeling of spin-transfer-torque (STT) driven reversal in nanopillars with strong out-of-plane magnetic anisotropy where the free layer is a magnetically hard-soft composite structure. By adjusting the exchange coupling between the hard and soft layers, we observed reduced current amplitude and pulse durations required to reverse the magnetization compared to a homogeneous free layer of comparable thermal stability. The reduction in critical current comes from the increased STT efficiency acting on the soft layer. As such, the switching current is relatively insensitive to the damping parameter of the magnetic hard layer. These properties make composite free layers promising candidates for STT-based magnetic memories.
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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.Ss Magnetic recording materials
75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Dynamic and temperature effects in microwave assisted switching: Evidence of chaotic macrospin dynamics

Dorin Cimpoesu and Alexandru Stancu

Appl. Phys. Lett. 99, 132503 (2011); http://dx.doi.org/10.1063/1.3640230 (3 pages) | Cited 3 times

Online Publication Date: 26 September 2011

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Microwave assisted switching (MAS) is a method that can be used in magnetic recording in order to reduce the writing field. In order to have a robust method, the factors influencing MAS have to be systematically analyzed. In this paper we use the stochastic Landau-Lifsitz-Gilbert simulations to examine MAS in terms of microwave amplitude and frequency, damping, and the parameters describing the pulse field. Also, we discuss about the troubling aspect of numerical induced chaos.
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75.50.Ss Magnetic recording materials
02.50.Ey Stochastic processes

Magnetic properties and magnetocaloric effects in R3Ni2 (R = Ho and Er) compounds

Q. Y. Dong, J. Chen, J. Shen, J. R. Sun, and B. G. Shen

Appl. Phys. Lett. 99, 132504 (2011); http://dx.doi.org/10.1063/1.3643142 (3 pages) | Cited 6 times

Online Publication Date: 26 September 2011

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Magnetic and magnetocaloric properties of R3Ni2 (R = Ho and Er) compounds have been investigated. Both Ho3Ni2 and Er3Ni2 compounds undergo two successive phase transitions: spin reorientation transition and second-order ferromagnetic-paramagnetic transition. The maximal values of magnetic entropy change are achieved to be 21.7 J kg−1 K−1 for Ho3Ni2 and 19.5 J kg−1 K−1 for Er3Ni2 for a field change of 0-5 T. A large refrigerant capacity (RC) of 496 J kg−1 in the composite material is also obtained. Large reversible magnetocaloric effect and RC indicate the potentiality of R3Ni2 (R = Ho and Er) compounds as candidates for low-temperature magnetic refrigerant.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Cc Other ferromagnetic metals and alloys
75.20.En Metals and alloys
75.30.Ds Spin waves
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Spin waves interference from rising and falling edges of electrical pulses

Jae Hyun Kwon, Sankha Subhra Mukherjee, Mahdi Jamali, Masamitsu Hayashi, and Hyunsoo Yang

Appl. Phys. Lett. 99, 132505 (2011); http://dx.doi.org/10.1063/1.3643156 (3 pages) | Cited 3 times

Online Publication Date: 26 September 2011

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The authors have investigated the effect of the electrical pulse width of input excitations on the generated spin waves in a NiFe strip using pulse inductive time domain measurements. The authors have shown that the spin waves resulting from the rising- and the falling-edges of input excitation pulses interfere either constructively or destructively and have provided conditions for obtaining spin wave packets with maximum intensity at different bias conditions.
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75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Bb Fe and its alloys

Effective cancellation of residual magnetic interference induced from a shielded environment for precision magnetic measurements

Seong-Min Hwang, Kiwoong Kim, Chan Seok Kang, Seong-Joo Lee, and Yong-Ho Lee

Appl. Phys. Lett. 99, 132506 (2011); http://dx.doi.org/10.1063/1.3643427 (3 pages) | Cited 2 times

Online Publication Date: 26 September 2011

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Using the method of inverse problem, we designed a cancellation coil that prevents a strong pulsed magnetic field inside a magnetically shielded room (MSR) from magnetizing and inducing large-scale eddy currents around the shielding materials. We implemented this coil with discrete current loops and evaluated it numerically and experimentally. Without the cancellation coil, the transient residual magnetic field in the middle of the MSR was greater than 0.1 μT for 63.5 ms, while the cancellation coil reduced it to less than 0.1 μT after 10.8 ms, shortening the decay time by 83.0%.
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41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Inter/intra granular exchange and thermal activation in nanoscale granular magnetic materials

C. Morrison, L. Saharan, G. Hrkac, T. Schrefl, Y. Ikeda, K. Takano, J. J. Miles, and T. Thomson

Appl. Phys. Lett. 99, 132507 (2011); http://dx.doi.org/10.1063/1.3644469 (3 pages) | Cited 2 times

Online Publication Date: 27 September 2011

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We explain the effect of inter/intra granular exchange coupling and thermal activation on the switching behavior of nano-scale granular magnetic materials. For an ideal, non-interacting granular system, the minimum switching field occurs at 45° from the easy axis of the grains. We show through simulation and measurements, using a CoCrPt oxide-segregated granular film as a model system, that there is a clear shift in the angle of applied field at which the minimum switching field occurs. This arises solely due to incoherent reversal induced by inter-granular exchange coupling or incoherency within larger grains, rather than thermal activation.
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75.30.Et Exchange and superexchange interactions
75.40.Mg Numerical simulation studies
75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.78.Jp Ultrafast magnetization dynamics and switching

Ferromagnetism in ZnO co-doped with Mn and N studied by soft x-ray magnetic circular dichroism

T. Kataoka, Y. Yamazaki, V. R. Singh, Y. Sakamoto, A. Fujimori, Y. Takeda, T. Ohkochi, S.-I. Fujimori, T. Okane, Y. Saitoh, H. Yamagami, A. Tanaka, M. Kapilashrami, L. Belova, and K. V. Rao

Appl. Phys. Lett. 99, 132508 (2011); http://dx.doi.org/10.1063/1.3643044 (3 pages) | Cited 3 times

Online Publication Date: 27 September 2011

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We have investigated the electronic structure of ZnO:Mn and ZnO:Mn,N thin films using x-ray magnetic circular dichroism (XMCD) and resonance-photoemission spectroscopy. From the Mn 2p → 3d XMCD results, it is shown that, while XMCD signals only due to paramagnetic Mn2+ ions were observed in ZnO:Mn, nonmagnetic, paramagnetic, and ferromagnetic Mn2+ ions coexist in ZnO:Mn,N. XMCD signals of ZnO:Mn,N revealed that the localized Mn2+ ground state and Mn2+ state hybridized with ligand hole coexisted, implying p-d exchange coupling. In the valence-band spectra, spectral weight near the Fermi level was suppressed, suggesting that interaction between magnetic moments in ZnO:Mn,N has localized nature.
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71.20.Nr Semiconductor compounds
71.70.Gm Exchange interactions
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
75.70.Ak Magnetic properties of monolayers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Exploring Co2MnAl Heusler compound for anomalous Hall effect sensors

E. Vilanova Vidal, G. Stryganyuk, H. Schneider, C. Felser, and G. Jakob

Appl. Phys. Lett. 99, 132509 (2011); http://dx.doi.org/10.1063/1.3644157 (3 pages) | Cited 3 times

Online Publication Date: 27 September 2011

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Sets of Heusler compound Co2MnAl thin films were grown on MgO (100) and Si (100) substrates by radio frequency magnetron sputtering. Composition, magnetic, and transport properties were studied systematically for samples deposited at different conditions. In particular, the anomalous Hall effect resistivity presents an extraordinarily temperature independent behavior in a moderate magnetic field range from 0 to 0.6 T. We analyzed the off-diagonal transport at temperatures up to 300 °C. Our data show the suitability of the material for Hall sensors working well above room temperature.
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85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
68.55.at Other materials
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.61.At Metal and metallic alloys
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Cd Deposition by sputtering

Unveiling the (De)coupling of magnetostructural transition nature in magnetocaloric R5Si2Ge2 (R = Tb, Gd) materials

A. M. Pereira, E. Kampert, J. M. Moreira, U. Zeitler, J. H. Belo, C. Magen, P. A. Algarabel, L. Morellon, M. R. Ibarra, J. N. Gonçalves, J. S. Amaral, V. S. Amaral, J. B. Sousa, and J. P. Araújo

Appl. Phys. Lett. 99, 132510 (2011); http://dx.doi.org/10.1063/1.3640213 (3 pages) | Cited 4 times

Online Publication Date: 28 September 2011

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We present a detailed study on the magnetization under high magnetic fields of Tb5Si2Ge2 and Gd5Si2Ge2 compounds. From the Arrott plot construction (A. Arrott, Phys. Rev. 108, 1394 (1957)), we were able to estimate the TC of each structure (M and O(I)) experimentally and found that the TC of the O(I) phase can be directly obtained by extrapolating the TC curve of this phase in the respective phase diagram. Using a physical model based on free energy considerations, one explains the (de)coupling of the magnetic and structural transitions in R5(SixGe1−x)4 (R = Tb, Gd) compounds.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
64.70.K- Solid-solid transitions
75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals
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