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13 Aug 2012

Volume 101, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 071104 (2012); http://dx.doi.org/10.1063/1.4742749 (4 pages)

Judson D. Ryckman and S. M. Weiss
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Development of metamaterials with desired broadband optical properties

Anatoliy V. Goncharenko, Vladimir U. Nazarov, and Kuan-Ren Chen

Appl. Phys. Lett. 101, 071907 (2012); http://dx.doi.org/10.1063/1.4746400 (5 pages) | Cited 1 time

Online Publication Date: 16 August 2012

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The development of metamaterials that possess desired optical properties over a spectral band is a problem of fundamental importance; its solution could considerably improve the performance of many existing optical devices and allow new devices. Dealing with nanostructured metal/dielectric composites (subwavelength photonic crystals) with a specified spatial configuration, within the framework of the effective medium theory, we obtain an approximation for their effective permittivity. Then, making use of this approximation, we propose a scheme for designing above metamaterials. As practically important particular examples, we consider quasi-one-dimensional metamaterials with ultralow refractive index, a high absorption, and those possessing pass-band filtering properties.
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42.70.Qs Photonic bandgap materials
02.60.Gf Algorithms for functional approximation

Radiation tolerance of ultra-thin Formvar films

M. Stadermann, S. O. Kucheyev, J. Lewicki, and S. A. Letts

Appl. Phys. Lett. 101, 071908 (2012); http://dx.doi.org/10.1063/1.4746403 (3 pages)

Online Publication Date: 16 August 2012

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Mechanical behavior of free-standing polymer films with submicron thicknesses exposed to a radiation environment is poorly understood. Here, we study 110-nm-thin free-standing polyvinyl formal (Formvar) films irradiated at room temperature with 1–5 keV electrons or 3 MeV alpha particles. We measure mechanical properties and the elemental composition by spherical indentation and high-energy ion scattering, respectively. Results show that, with increasing radiation dose, the effective failure strain and film thickness decrease monotonically, while the dose dependence of the Young’s modulus is non-monotonic. The failure strain and modulus scale with the average energy deposited in the film, while the film thickness exhibits a more complex behavior.
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61.80.Fe Electron and positron radiation effects
61.82.Pv Polymers, organic compounds
62.20.Qp Friction, tribology, and hardness
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.de Elastic moduli

Strain induced tetragonal SrTiO3 nanoparticles at room temperature

Cailei Yuan, Shuangli Ye, Bo Xu, and Wen Lei

Appl. Phys. Lett. 101, 071909 (2012); http://dx.doi.org/10.1063/1.4747204 (4 pages)

Online Publication Date: 17 August 2012

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SrTiO3 nanoparticles with tetragonal phase at room temperature were fabricated using pulsed laser deposition method and rapid thermal annealing technique. High-resolution transmission electron microscope images demonstrate that SrTiO3 nanoparticle experiences a structural phase transition from cubic with indirect band gap to tetragonal with direct band gap with growing size. It has been found that the net deviatoric strain from Lu2O3 matrix can cause the rotation of the TiO6 octahedra and the change of the bond length, which is suggested to explain the structural phase transition. Strain engineering is an effective tool for tailoring the properties of SrTiO3 nanoparticles.
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77.80.bn Strain and interface effects
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.72.Cc Kinetics of defect formation and annealing
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
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Impact of substrate-induced strain and surface effects on the optical properties of InP nanowires

Roman Anufriev, Nicolas Chauvin, Hammadi Khmissi, Khalid Naji, Michel Gendry, and Catherine Bru-Chevallier

Appl. Phys. Lett. 101, 072101 (2012); http://dx.doi.org/10.1063/1.4745608 (4 pages) | Cited 2 times

Online Publication Date: 13 August 2012

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Wurtzite InP nanowires (NWs), transferred onto various substrates, were investigated by low temperature micro-photoluminescence. A clear PL emission shift, depending on the substrate, is observed and attributed to the substrate-induced strain, generated due to the difference in the thermal expansion coefficients of the InP NWs and the host-substrate during the sample cooling. Moreover, a blueshift of the PL emission peak is observed as the excitation power is increased. This effect, which is not observed on the as-grown sample, is thus a consequence of the host substrate and not an intrinsic property of the nanowires.
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78.55.Cr III-V semiconductors
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
78.67.Uh Nanowires
65.40.De Thermal expansion; thermomechanical effects
68.47.Fg Semiconductor surfaces

Magnetically active vacancy related defects in irradiated GaN layers

L. Kilanski, F. Tuomisto, R. Szymczak, and R. Kruszka

Appl. Phys. Lett. 101, 072102 (2012); http://dx.doi.org/10.1063/1.4745776 (3 pages) | Cited 1 time

Online Publication Date: 13 August 2012

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We present the studies of magnetic properties of 2 MeV 4He+-irradiated GaN grown by metal-organic chemical-vapor deposition. Particle irradiation allowed controllable introduction of Ga-vacancy in the samples. The magnetic moments with concentrations changing between 4.3 and 8.3×1017cm−3 showing superparamagnetic blocking at room temperature are observed. The appearance of clear hysteresis curve at T = 5K with coercive field of about HC ≈ 270 Oe suggests that the formation of more complex Ga vacancy related defects is promoted with increasing Ga vacancy content. The small concentration of the observed magnetically active defects with respect to the total Ga-vacancy concentration suggests that the presence of the oxygen/hydrogen-related vacancy complexes is the source of the observed magnetic moments.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.05.Ea III-V semiconductors
61.72.jd Vacancies
61.82.Fk Semiconductors

Measurement of the Schottky barrier height between Ni-InGaAs alloy and In0.53Ga0.47As

Shlomo Mehari, Arkady Gavrilov, Shimon Cohen, Pini Shekhter, Moshe Eizenberg, and Dan Ritter

Appl. Phys. Lett. 101, 072103 (2012); http://dx.doi.org/10.1063/1.4746254 (4 pages) | Cited 2 times

Online Publication Date: 14 August 2012

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The temperature dependence of the current-voltage characteristics of Ni-InGaAs alloy Schottky contacts to n-In0.53Ga0.47As was measured. Nearly ideal plots with an ideality factor close to unity were obtained. The Arrhenius curve across the wide temperature range of 80–300 K was perfectly linear, yielding a barrier height of 0.239 ± 0.01 eV. This value is substantially larger than previously reported. Conventional metal based Schottky diodes did not exhibit an ideal Schottky behavior. The ideal Schottky diode characteristics are attributed to the lack of oxidation and contamination of the interface between Ni-InGaAs and InGaAs.
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73.30.+y Surface double layers, Schottky barriers, and work functions

Fluorine passivation of vacancy defects in bulk germanium for Ge metal-oxide-semiconductor field-effect transistor application

Woo-Shik Jung, Jin-Hong Park, Aneesh Nainani, Donguk Nam, and Krishna C. Saraswat

Appl. Phys. Lett. 101, 072104 (2012); http://dx.doi.org/10.1063/1.4746389 (3 pages) | Cited 4 times

Online Publication Date: 15 August 2012

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Vacancy defects in germanium (Ge) adversely impact the electrical performance of Ge based metal-oxide-semiconductor field-effect transistor (MOSFET) in several ways. They behave as an acceptor site, thereby deactivating n-type dopants in the source/drain region. They can also increase substrate leakage currents and impact carrier lifetime in the channel region. In this paper, we characterize and verify the electrical behavior of vacancy defects in Ge using spreading resistance profiling (SRP). Effect of thermal annealing on the vacancy concentration is studied. Finally, passivation of these defects using fluorine (F) ion-implant is shown to demonstrate the feasibility of performance enhancement in Ge-MOSFETs.
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81.65.Rv Passivation
85.30.Tv Field effect devices
61.72.jd Vacancies
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
81.05.Cy Elemental semiconductors

Next generation of Ge1−ySny (y = 0.01-0.09) alloys grown on Si(100) via Ge3H8 and SnD4: Reaction kinetics and tunable emission

G. Grzybowski, R. T. Beeler, L. Jiang, D. J. Smith, J. Kouvetakis, and J. Menéndez

Appl. Phys. Lett. 101, 072105 (2012); http://dx.doi.org/10.1063/1.4745770 (5 pages) | Cited 1 time

Online Publication Date: 16 August 2012

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Film growth and reaction kinetics studies have shown that trigermane (Ge3H8) is a superior Ge source for the epitaxial synthesis of Ge1−ySny/Si(100) alloys using ultra-high vacuum chemical vapor deposition. The Ge3H8/SnD4 combination yields 3-4 times higher growth rates than the traditional Ge2H6/SnD4 approach, with film Sn/Ge ratios reflecting the corresponding gas-phase stoichiometries much more closely. These advances have led to optical quality Ge1−ySny layers with Sn concentrations up to at least 9% and thicknesses approaching 1 μm. These thick films are found to be crucial for the observation of a strong, tunable photoluminescence signal near the threshold of the predicted direct-indirect bandgap crossover.
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68.55.ag Semiconductors
78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Highly (111)-oriented Ge thin films on insulators formed by Al-induced crystallization

K. Toko, M. Kurosawa, N. Saitoh, N. Yoshizawa, N. Usami, M. Miyao, and T. Suemasu

Appl. Phys. Lett. 101, 072106 (2012); http://dx.doi.org/10.1063/1.4744962 (3 pages) | Cited 1 time

Online Publication Date: 16 August 2012

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(111)-oriented Ge thin films on insulators are essential for advanced electronics and photovoltaic applications. We investigate Al-induced crystallization of amorphous-Ge films (50-nm thickness) on insulators focusing on the annealing temperature and the diffusion controlling process between Ge and Al. The (111)-orientation fraction of the grown Ge layer reaches as high as 99% by combining the low-temperature annealing (325 °C) and the native-oxidized Al (AlOx) diffusion-control layer. Moreover, the transmission electron microscopy reveals the absence of defects on the Ge surface. This (111)-oriented Ge on insulators promises to be the high-quality epitaxial template for various functional materials to achieve next-generation devices.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Pz Photoconduction and photovoltaic effects
61.72.Cc Kinetics of defect formation and annealing
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.Fx Diffusion; interface formation

Lateral transport properties of Nb-doped rutile- and anatase-TiO2 films epitaxially grown on c-plane GaN

K. Hazu, T. Ohtomo, T. Nakayama, A. Tanaka, and S. F. Chichibu

Appl. Phys. Lett. 101, 072107 (2012); http://dx.doi.org/10.1063/1.4746406 (4 pages)

Online Publication Date: 16 August 2012

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Valence-band offsets for Nb-doped (100) rutile (R-TiO2) epilayer on (0001) GaN and (001) anatase (A-TiO2) epilayer mixed with R-TiO2 on (0001) GaN were determined using x-ray photoelectron spectroscopy to be +0.2 eV and +0.6 eV, respectively. Accordingly, they form type-I and type-II heterojunctions, respectively. The electron mobility as high as 260 cm2 V−1 s−1 was measured for the A(+R)-TiO2:Nb epilayer on undoped GaN, which is quantitatively explained in terms of electron accumulation at the interfacial region of GaN. The intrinsic mobility of approximately 30 cm2 V−1 s−1 at 300 K was obtained for the A(+R)-TiO2:Nb epilayer grown on a p-type GaN.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures
68.55.A- Nucleation and growth
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Damping modulated terahertz emission of ferromagnetic films excited by ultrafast laser pulses

Jian Shen, Xin Fan, Zhiyuan Chen, Matthew F. DeCamp, Huaiwu Zhang, and John Q. Xiao

Appl. Phys. Lett. 101, 072401 (2012); http://dx.doi.org/10.1063/1.4737400 (4 pages) | Cited 1 time

Online Publication Date: 13 August 2012

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Ultrafast demagnetization processes in ferromagnetic films have been shown to produce terahertz (THz) emission. We present an experimental demonstration that, following ultrafast optical excitation, the magnitude of terahertz electromagnetic pulses emitted from a ferromagnetic film is proportional to the Gilbert damping constant, which is conventionally used to describe the damping of magnetization precession. The damping of a ferromagnetic thin film is tuned by using an adjacent nonmagnetic layer, which does not change the magnetization and anisotropy of the ferromagnetic film, allowing an unambiguous determination of the relationship between the THz emission and the damping constant.
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78.70.Gq Microwave and radio-frequency interactions
78.47.J- Ultrafast spectroscopy (<1 psec)
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Non-volatile voltage control of magnetization and magnetic domain walls in magnetostrictive epitaxial thin films

D. E. Parkes, S. A. Cavill, A. T. Hindmarch, P. Wadley, F. McGee, C. R. Staddon, K. W. Edmonds, R. P. Campion, B. L. Gallagher, and A. W. Rushforth

Appl. Phys. Lett. 101, 072402 (2012); http://dx.doi.org/10.1063/1.4745789 (4 pages) | Cited 4 times

Online Publication Date: 13 August 2012

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We demonstrate reproducible voltage induced non-volatile switching of the magnetization in an epitaxial thin Fe81Ga19 film. Switching is induced at room temperature and without the aid of an external magnetic field. This is achieved by the modification of the magnetic anisotropy by mechanical strain induced by a piezoelectric transducer attached to the layer. Epitaxial Fe81Ga19 is shown to possess the favourable combination of cubic magnetic anisotropy and large magnetostriction necessary to achieve this functionality with experimentally accessible levels of strain. The switching of the magnetization proceeds by the motion of magnetic domain walls, also controlled by the voltage induced strain.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure

Ferromagnetic properties of GdN thin films studied by temperature dependent circular polarized spectroscopy

H. Yoshitomi, R. Vidyasagar, S. Kitayama, T. Kita, H. Ohta, S. Okubo, Y. Fukuoka, and T. Sakurai

Appl. Phys. Lett. 101, 072403 (2012); http://dx.doi.org/10.1063/1.4746265 (5 pages) | Cited 2 times

Online Publication Date: 13 August 2012

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Magneto-optical properties of GdN thin films have been investigated by employing temperature dependent optical circular dichroism spectroscopy and angular dependent resonance field measurement. Spin-splitting in the band structure of GdN thin films has been evaluated by optical circular dichroism absorbance spectra, and the manifested spin-splitting energy ascribed to the difference between majority and minority spin band states in GdN. The plot of left circular polarization and right circular polarization bandgap reflects the half-hysteresis loop (positive side) trend, which is evidenced by magnetization measurements. The angular dependent resonance field measurements showed strong magnetic anisotropy along in-plane of GdN, which is attributed to the disturbance in the spin alignment in GdN. We demonstrate that the ferromagnetic properties depend on the film thickness. These results provide a pathway to control the spin ordering using circularly polarized light and the magnetic anisotropy.
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75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
78.66.Li Other semiconductors
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors

Mechanism of magnetoresistance ratio enhancement in MgO/NiFe/MgO heterostructure by rapid thermal annealing

Chong-Jun Zhao, Yang Liu, Jing-Yan Zhang, Li Sun, Lei Ding, Peng Zhang, Bao-Yi Wang, Xing-Zhong Cao, and Guang-Hua Yu

Appl. Phys. Lett. 101, 072404 (2012); http://dx.doi.org/10.1063/1.4745916 (5 pages) | Cited 2 times

Online Publication Date: 14 August 2012

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To reveal thermal effects on the film quality/microstructure evolution and the resulted magnetoresistance (MR) ratio in MgO/NiFe/MgO heterostructures, positron annihilation spectroscopy studies have been performed. It is found that the ionic interstitials in the MgO layers recombine with the nearby vacancies at lower annealing temperatures (200-300 °C) and lead to a slow increase in sample MR. Meanwhile, vacancy defects agglomeration/removal and ordering acceleration in MgO will occur at higher annealing temperatures (450-550 °C) and the improved MgO and MgO/NiFe interfaces microstructure are responsible for the observed significant MR enhancement.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.21.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.70.Bj Positron annihilation
61.72.jd Vacancies
61.72.jj Interstitials
61.72.Cc Kinetics of defect formation and annealing

High magnetostriction and coupling coefficient for sintered cobalt ferrite derived from superparamagnetic nanoparticles

K. Khaja Mohaideen and P. A. Joy

Appl. Phys. Lett. 101, 072405 (2012); http://dx.doi.org/10.1063/1.4745922 (4 pages) | Cited 1 time

Online Publication Date: 14 August 2012

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High magnetostriction (λ) and coupling coefficient (dλ/dH) of 315 ppm and 1.97×10−9 A−1m, respectively, are obtained at room temperature for sintered cobalt ferrite derived from nanocrystalline powders. Also, the powder was compacted at a low pressure of 8 MPa and sintered for a short duration of 10 min at 1450 °C. Magnetic annealing at 300 °C in a field of 0.5 T for 30 min further enhanced the magnetostriction coefficient to 345 ppm with a higher coupling coefficient 2.12×10−9 A−1m. The magnetic field above which maximum magnetostriction is observed is reduced by almost half after magnetic annealing.
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75.80.+q Magnetomechanical effects, magnetostriction
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
75.20.Ck Nonmetals
75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Nt Magnetic annealing and temperature-hysteresis effects

Carriers dependence of the magnetic properties in magnetic topological insulator Sb1.95−xBixCr0.05Te3

H. Li, Y. R. Song, Meng-Yu Yao, Fang Yang, Lin Miao, Fengfeng Zhu, Canhua Liu, C. L. Gao, Dong Qian, X. Yao, Jin-Feng Jia, Y. J. Shi, and D. Wu

Appl. Phys. Lett. 101, 072406 (2012); http://dx.doi.org/10.1063/1.4746404 (4 pages) | Cited 1 time

Online Publication Date: 14 August 2012

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Bulk carrier density and magnetic properties of Sb1.95−xBixCr0.05Te3 single crystals were studied. We found that the carrier density can be tuned by Bi substitution. Both the Curie temperature and magnetic moments are strongly related to the carrier density, which suggests the existence of intrinsic ferromagnetism in Cr-doped Sb2Te3 magnetic topological insulator that is very important for spin-related applications.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Probing a single nuclear spin in a silicon single electron transistor

F. Delgado, R. Aguado, and J. Fernández-Rossier

Appl. Phys. Lett. 101, 072407 (2012); http://dx.doi.org/10.1063/1.4746260 (4 pages)

Online Publication Date: 16 August 2012

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We study single electron transport across a single Bi dopant in a silicon nanotransistor to assess how the strong hyperfine coupling with the Bi nuclear spin I = 9/2 affects the transport characteristics of the device. In the sequential tunneling regime we find that at, temperatures in the range of 100 mK, dI/dV curves reflect the zero field hyperfine splitting as well as its evolution under an applied magnetic field. Our non-equilibrium quantum simulations show that nuclear spins can be partially polarized parallel or antiparallel to the electronic spin just tuning the applied bias.
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85.35.Gv Single electron devices
85.30.De Semiconductor-device characterization, design, and modeling

Fast domain wall dynamics in MnAs/GaAs films

M. Tortarolo, L. Thevenard, H. J. von Bardeleben, M. Cubukcu, V. Etgens, M. Eddrief, and C. Gourdon

Appl. Phys. Lett. 101, 072408 (2012); http://dx.doi.org/10.1063/1.4746381 (4 pages)

Online Publication Date: 16 August 2012

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Field-induced domain wall (DW) dynamics was investigated in MnAs/GaAs(100) films by means of longitudinal Kerr microscopy and a field pulse technique. Saw-tooth type domains were observed in the studied temperature range. DW velocities up to 950 m s−1 were measured at 200 K and up to 540 m s−1 at 290 K, at the beginning of the nucleation of the non-ferromagnetic β phase within the ferromagnetic α phase. Different propagation regimes were observed depending on the magnitude of the Walker field compared to the depinning field, which depends on the progressive nucleation of an unordered β phase. The results are interpreted in the framework of the one-dimensional model (1D) for DW propagation.
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75.60.Ch Domain walls and domain structure
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
64.60.Q- Nucleation
75.78.Fg Dynamics of domain structures
75.50.Dd Nonmetallic ferromagnetic materials

Spin-torque effect on spin wave modes in magnetic nanowires

Voicu O. Dolocan

Appl. Phys. Lett. 101, 072409 (2012); http://dx.doi.org/10.1063/1.4747152 (4 pages)

Online Publication Date: 17 August 2012

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The interaction between a spin polarized dc electrical current and spin wave modes of a cylindrical nanowire is investigated in this report. We found that close to the critical current, the uniform mode is suppressed, while the edge mode starts to propagate into the sample. When the current exceeds the critical value, this phenomenon is even more accentuated. The edge mode becomes the uniform mode of the nanowire. The higher spin wave modes are slowly pushed away by the current until the propagating mode remains.
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75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures
72.25.-b Spin polarized transport

Enhancement of perpendicular magnetic anisotropy thanks to Pt insertions in synthetic antiferromagnets

S. Bandiera, R. C. Sousa, S. Auffret, B. Rodmacq, and B. Dieny

Appl. Phys. Lett. 101, 072410 (2012); http://dx.doi.org/10.1063/1.4745924 (4 pages)

Online Publication Date: 17 August 2012

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Synthetic antiferromagnets are of great interest as reference layers in magnetic tunnel junctions since they allow decreasing the dipolar coupling between the two magnetic electrodes and exhibit larger pinning fields than single reference layers. In this letter, we investigate the effect of the insertion of an ultrathin Pt layer in contact with the Ru spacer in synthetic antiferromagnets with perpendicular magnetic anisotropy. Surprisingly, for Ru thickness below 0.75 nm, the antiferromagnetic coupling amplitude through Ru first increases upon Pt insertion up to a critical Pt thickness (∼0.25 nm) above which coupling decreases. In addition, the corresponding increase of perpendicular magnetic anisotropy enhances the thermal stability of the structure.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics

Optimization of Ta thickness for perpendicular magnetic tunnel junction applications in the MgO-FeCoB-Ta system

Vincent Sokalski, Matthew T. Moneck, En Yang, and Jian-Gang Zhu

Appl. Phys. Lett. 101, 072411 (2012); http://dx.doi.org/10.1063/1.4746426 (4 pages) | Cited 2 times

Online Publication Date: 17 August 2012

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The impact of Ta thickness on magnetic anisotropy and interlayer magnetic coupling is evaluated for the Ta-FeCoB-MgO thin film system commonly used in magnetic tunnel junctions. It is shown that there exists a window of Ta thickness where strong magnetic coupling of FeCoB with another magnetic layer is achievable through Ta while still maintaining properties required for use in a perpendicular magnetic tunnel junction. We also expand on existing knowledge about the role of annealing temperature, film composition, and seedlayer sequence on magnetic anisotropy in Ta/FeCoB/MgO tri-layers of varying FeCoB thickness.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
75.30.Gw Magnetic anisotropy

Magnetic reversal in a YFe2 dominated DyFe2/YFe2 multilayer film

G. B. G. Stenning, G. J. Bowden, S. A. Gregory, J.-M. L. Beaujour, P. A. J. de Groot, G. van der Laan, L. R. Shelford, P. Bencok, P. Steadman, A. N. Dobrynin, and T. Hesjedal

Appl. Phys. Lett. 101, 072412 (2012); http://dx.doi.org/10.1063/1.4746749 (4 pages) | Cited 2 times

Online Publication Date: 17 August 2012

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Magnetic reversal in a (110)-oriented [DyFe2(60 Å)/YFe2(240 Å)]×15 multilayer film is investigated using magnetometry, micro-magnetic modeling, and element-specific soft x-ray magnetic circular dichroism. At temperatures between ∼60 and 120 K, the magnetic reversal involves a two-step process. It is shown that the reversal mechanism can be described as switching from an in-plane [001] reversed anti-ferromagnetic state, to an out-of-plane [100] transverse spring exchange state, and finally to an in-plane [00math] magnetic exchange spring state.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.60.Jk Magnetization reversal mechanisms
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Bias-current effect on inverse spin-switch effect in Permalloy/Nb/Permalloy pseudo spin-valves

Tae-Jong Hwang and D. H. Kim

Appl. Phys. Lett. 101, 072601 (2012); http://dx.doi.org/10.1063/1.4745610 (4 pages)

Online Publication Date: 14 August 2012

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The magnetoresistance of Permalloy/Nb/Permalloy pseudo spin-valves in the superconducting transition region have been measured in sweeping magnetic fields while varying bias current in order to investigate bias-current effect on the inverse spin-switch behavior. The magnetoresistance measured between two notches in a micron-size bar showed an ideal inverse spin-switch effect between two magnetic states of Permalloy layers, parallel and antiparallel domain state, at high enough bias-current densities exceeding 105 A/cm2, in which the antiparallel domain state returns to the normal whereas the parallel state remains superconducting.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
74.20.Mn Nonconventional mechanisms
75.47.De Giant magnetoresistance
75.60.Ch Domain walls and domain structure

Photon-number resolving detector based on a series array of superconducting nanowires

S. Jahanmirinejad, G. Frucci, F. Mattioli, D. Sahin, A. Gaggero, R. Leoni, and A. Fiore

Appl. Phys. Lett. 101, 072602 (2012); http://dx.doi.org/10.1063/1.4746248 (4 pages) | Cited 3 times

Online Publication Date: 14 August 2012

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We present the experimental demonstration of a superconducting photon number resolving detector. It is based on the series connection of N superconducting nanowires, each connected in parallel to an integrated resistor. The device provides a single voltage readout, proportional to the number of photons detected in distinct nanowires. Clearly separated output levels corresponding to the detection of n = 1−4 photons are observed in a 4-element detector fabricated from an NbN film on GaAs substrate, with a single-photon system quantum efficiency of 2.6% at λ = 1.3 μm. The series-nanowire structure is promising in view of its scalability to large photon numbers and high efficiencies.
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07.60.Dq Photometers, radiometers, and colorimeters
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
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Enhancement of magnetoresistance using CoFe/Ru/CoFe synthetic ferrimagnetic pinned layer in BiFeO3 based spin-valves

Hiroshi Naganuma, In-Tae Bae, Takamichi Miyazaki, Miho Kubota, Nobuhito Inami, Yuki Kawada, Mikihiko Oogane, Shigemi Mizukami, X. F. Han, and Yasuo Ando

Appl. Phys. Lett. 101, 072901 (2012); http://dx.doi.org/10.1063/1.4745504 (3 pages)

Online Publication Date: 13 August 2012

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SrTiO3 (100) sub/BiFeO3/CoFe/Ru/CoFe/Cu/CoFe/Ta structure was prepared by a combination of chemical solution deposition and sputtering method, and followed by a systematical investigation for the structural, magnetic and magnetoresistance properties at room temperature (RT) as a function of CoFe and Ru thicknesses. It was revealed that introduction of synthetic CoFe/Ru/CoFe as a pinning layer increased the giant magentoresistance (MR) ratio to 8.3% at RT. This enhancement of MR ratio might be attributed to (i) the increase of pinning field, and (ii) suppression of the influence of the surface roughness of BiFeO3 by inserting the synthetic CoFe/Ru/CoFe layer.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.47.De Giant magnetoresistance
75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
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