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14 May 2012

Volume 100, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 203104 (2012); http://dx.doi.org/10.1063/1.3701731 (4 pages)

Z. Y. Jiang, X. X. Jiang, S. Su, X. P. Wei, S. T. Lee, and Y. He
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Optical and acoustic phonon modes in strained InGaAs/GaAs rolled up tubes

T. Angelova, N. Shtinkov, Ts. Ivanov, V. Donchev, A. Cantarero, Ch. Deneke, O. G. Schmidt, and A. Cros

Appl. Phys. Lett. 100, 201904 (2012); http://dx.doi.org/10.1063/1.4714542 (4 pages) | Cited 1 time

Online Publication Date: 14 May 2012

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Rolled-up semiconductor tubes of various diameters made of alternating In0.215Ga0.785As/GaAs layers have been investigated by means of Raman scattering. The optical and acoustic phonon modes of individual tubes have been studied and compared with the characteristics of the surrounding material. After tube formation, the frequency of the phonon modes shifts with respect to the as-grown material and disorder activated modes are observed. The frequency shifts are related to the residual strain in the tubes through the deformation potential approximation. Good agreement with atomistic valence force field simulations and x-ray micro-diffraction measurements is found. By comparison with x-ray data, a Raman strain constant K = 0.65 is proposed for In0.215Ga0.785As. In the low frequency range, acoustic mode doublets are observed on the tubes that are absent in the surrounding material. They show clear evidence of the formation of periodic superlattices after the rolling-up process, and give insight into the quality of their interfaces.
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78.66.Fd III-V semiconductors
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.65.Cd Superlattices
78.30.-j Infrared and Raman spectra
78.30.Fs III-V and II-VI semiconductors

Magnitude-tunable sub-THz shear phonons in a non-polar GaN multiple-quantum-well p-i-n diode

Chien-Cheng Chen, Huei-Min Huang, Tien-Chang Lu, Hao-Chung Kuo, and Chi-Kuang Sun

Appl. Phys. Lett. 100, 201905 (2012); http://dx.doi.org/10.1063/1.4718524 (4 pages) | Cited 1 time

Online Publication Date: 15 May 2012

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Coherent transverse acoustic phonons are optically generated and detected through the piezoelectric coupling between the build-in electric fields and shear strains of a non-polar GaN multiple quantum wells embedded in a p-n junction. By optical transient transmission change measurement, the phonon frequency is observed to be 0.4 THz which corresponds to a wavelength of 12.5 nm, the periodicity of the multiple quantum wells, and the estimated phonon velocity corresponds to the transverse acoustic phonon velocity in GaN. Moreover, we can magnify the driving amplitude of the generated shear phonons by increasing the reverse bias of the p-i-n diode.
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85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Anomalous phase change characteristics in Fe-Te materials

X. T. Fu, W. D. Song, H. W. Ho, R. Ji, L. Wang, and M. H. Hong

Appl. Phys. Lett. 100, 201906 (2012); http://dx.doi.org/10.1063/1.4719074 (4 pages) | Cited 1 time

Online Publication Date: 16 May 2012

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Phase change materials have become significantly attractive due to its unique characteristics for its extensive applications. In this paper, a kind of phase change material, which consists of Fe and Te components, is developed. The crystallization temperature of the Fe-Te materials is 180 °C for Fe1.19Te and can be adjusted by the Fe/Te ratio. High-speed phase change in the Fe-Te materials has been demonstrated by nanosecond laser irradiation. Comparing to conventional phase change materials, the Fe-Te materials exhibit an anomalous optical property that has higher reflectivity at amorphous than crystalline state, which is useful for data storage design.
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61.43.-j Disordered solids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.40.Kc Metals, semimetals, and alloys

Nano-sized Ba2NaNb5O15–NaNbO3 co-crystallized glass-ceramics in phosphoniobate system

Yoshihiro Takahashi, Nobuhiro Fujie, and Takumi Fujiwara

Appl. Phys. Lett. 100, 201907 (2012); http://dx.doi.org/10.1063/1.4719034 (4 pages) | Cited 2 times

Online Publication Date: 17 May 2012

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Glass-ceramics (GC) consisting of nano-sized Nb-dielectrics were fabricated in BaO–Na2O–P2O5–Nb2O5 system, and their crystallization and physical features were studied. Precursor of 0.67(2BaO–0.5Na2O)–1P2O5–2.5Nb2O5 glass co-crystallized Ba2NaNb5O15 (BNN) and NaNbO3 phases, which are about 10 nm in size, and resulting GC possessed an optical transparency comparable to the precursor glass, and optical band-gap of the GC was close to that of BNN. It is suggested that the fabricated GC is not merely a GC with transparency but Nb-dielectric GC, in which light scattering due to the crystallized phases evolution is minimized, i.e., practically transparent GC material.
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81.07.Bc Nanocrystalline materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Carbon nanotube fibers as torsion sensors

A. S. Wu, X. Nie, M. C. Hudspeth, W. W. Chen, T.-W. Chou, D. S. Lashmore, M. W. Schauer, E. Towle, and J. Rioux

Appl. Phys. Lett. 100, 201908 (2012); http://dx.doi.org/10.1063/1.4719058 (4 pages) | Cited 1 time

Online Publication Date: 17 May 2012

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Carbon nanotube fibers possess the ability to respond electrically to tensile loading. This research explores their electrical response to torsional loading; results demonstrate that applied twist compacts the fiber, resulting in increased electrical contact between carbon nanotubes. Shear strains in excess of 24% do not result in permanent changes in electrical resistance along uninfused fibers, while irreversible changes in electrical resistance arise from applied shear strains of 12.9% in epoxy infused fibers. Bulk shear modulus is approximated to be 0.40 ± 0.02 GPa for unreinforced and 2.79 ± 0.64 GPa for infused fibers.
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07.10.Cm Micromechanical devices and systems

Three-dimensional distribution of Al in high-k metal gate: Impact on transistor voltage threshold

F. Panciera, S. Baudot, K. Hoummada, M. Gregoire, M. Juhel, and D. Mangelinck

Appl. Phys. Lett. 100, 201909 (2012); http://dx.doi.org/10.1063/1.4717742 (4 pages) | Cited 1 time

Online Publication Date: 18 May 2012

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The three-dimensional spatial distribution of Al in the high-k metal gates of metal-oxide-semiconductor field-effect-transistors is measured by atom probe tomography. Chemical distribution is correlated with the transistor voltage threshold (VTH) shift generated by the introduction of a metallic Al layer in the metal gate. After a 1050 °C annealing, it is shown that a 2-Å thick Al layer completely diffuses into oxide layers, while a positive VTH shift is measured. On the contrary, for thicker Al layers, Al precipitation in the metal gate stack is observed and the VTH shift becomes negative.
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85.30.Tv Field effect devices
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Partially filled intermediate band of Cr-doped GaN films

S. Sonoda

Appl. Phys. Lett. 100, 202101 (2012); http://dx.doi.org/10.1063/1.4717716 (4 pages) | Cited 1 time

Online Publication Date: 14 May 2012

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We investigated the band structure of sputtered Cr-doped GaN (GaCrN) films using optical absorption, photoelectron yield spectroscopy, and charge transport measurements. It was found that an additional energy band is formed in the intrinsic band gap of GaN upon Cr doping, and that charge carriers in the material move in the inserted band. Prototype solar cells showed enhanced short circuit current and open circuit voltage in the n-GaN/GaCrN/p-GaN structure compared to the GaCrN/p-GaN structure, which validates the proposed concept of an intermediate-band solar cell.
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81.05.Ea III-V semiconductors
81.15.Cd Deposition by sputtering
88.40.jm Thin film III-V and II-VI based solar cells
71.20.Nr Semiconductor compounds
78.66.Fd III-V semiconductors
79.60.Dp Adsorbed layers and thin films

Electronic effects of Se and Pb dopants in TlBr

Holland M. Smith, III, David J. Phillips, Ian D. Sharp, Jeffrey W. Beeman, Daryl C. Chrzan, Nancy M. Haegel, Eugene E. Haller, Guido Ciampi, Hadong Kim, and Kanai S. Shah

Appl. Phys. Lett. 100, 202102 (2012); http://dx.doi.org/10.1063/1.4712596 (4 pages) | Cited 2 times

Online Publication Date: 14 May 2012

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Deep levels in Se- and Pb-doped bulk TlBr detectors were characterized with photo-induced conductivity transient spectroscopy (PICTS) and cathodoluminescence (CL). Se-doped TlBr revealed two traps with energies of 0.35 and 0.45 eV in PICTS spectra. The Pb-doped material revealed three levels with energies of 0.11, 0.45, and 0.75 eV. CL measurements in both materials correlate with optical transitions involving some of the identified levels. The ambipolar carrier lifetimes of Se-doped and Pb-doped TlBr were measured with microwave reflectivity transients and found to be significantly lower than the lifetime of undoped TlBr.
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71.55.Ht Other nonmetals
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.60.Hk Cathodoluminescence, ionoluminescence
71.20.Nr Semiconductor compounds

Trace analysis of non-basal plane misfit stress relaxation in (20math1) and (30mathmath) semipolar InGaN/GaN heterostructures

Matthew T. Hardy, Po Shan Hsu, Feng Wu, Ingrid L. Koslow, Erin C. Young, Shuji Nakamura, Alexey E. Romanov, Steven P. DenBaars, and James S. Speck

Appl. Phys. Lett. 100, 202103 (2012); http://dx.doi.org/10.1063/1.4716465 (4 pages) | Cited 9 times

Online Publication Date: 14 May 2012

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We have studied primary and secondary slip systems in the relaxation of lattice mismatch stresses in (20math1) and (30mathmath) semipolar InxGa1−xN/GaN heterostructures by analyzing the geometry of traces associated with dislocations employing cathodoluminescence, x-ray diffraction, and transmission electron microscopy. For (20math1) InxGa1−xN/GaN heterostructures, the primary relaxation is by dislocation glide on the c-plane 11math0(0001) slip system and secondary relaxation is by dislocation glide on inclined planes including the m-plane 〈11math0〉{1math00} slip system. For (30mathmath) grown heterostructures non-basal slip, namely dislocation glide on the m-plane slip system, is the initial stress relaxation pathway.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.Ct Interface structure and roughness
78.60.Hk Cathodoluminescence, ionoluminescence

Charge instability of atomic-layer deposited TaSiOx insulators on Si, InP, and In0.53Ga0.47As

V. V. Afanas’ev, H.-Y. Chou, N. H. Thoan, C. Adelmann, H. C. Lin, M. Houssa, and A. Stesmans

Appl. Phys. Lett. 100, 202104 (2012); http://dx.doi.org/10.1063/1.4710553 (4 pages) | Cited 1 time

Online Publication Date: 15 May 2012

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Low barriers for electrons are found to be the reason for significant charge instability at interfaces of (100)InP and (100)In0.53Ga0.47As with atomic-layer deposited TaSiOx insulators. The formation of these reduced barriers is associated with the growth of a narrow-bandgap interlayer between the semiconductor and TaSiOx, which enables electron tunneling at low electric fields and subsequent trapping in the insulator. A wide-gap passivation layer may be required to improve the performance of TaSiOx as gate insulator.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Dynamics of localized excitons in Ga0.69In0.31N0.015As0.985/GaAs quantum well: Experimental studies and Monte-Carlo simulations

M. Baranowski, R. Kudrawiec, M. Latkowska, M. Syperek, J. Misiewicz, and J. A. Gupta

Appl. Phys. Lett. 100, 202105 (2012); http://dx.doi.org/10.1063/1.4714739 (5 pages) | Cited 1 time

Online Publication Date: 15 May 2012

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Time resolved photoluminescence (PL) spectroscopy has been applied to study dynamics of localized excitons in a single Ga0.7In0.3N0.015As0.985/GaAs quantum well (QW). The decay time constant, τPL, has been determined for different PL peak energies at various temperatures. An increase in temperature produced two effects: (i) a reduction of τPL and (ii) changes in the τPL dispersion. These two experimental observations as well as the shape of PL decay curves were very well reproduced by Monte-Carlo simulations of hopping excitons with parameters derived from PL and photoreflectance measurements for this QW.
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78.67.De Quantum wells
78.47.J- Ultrafast spectroscopy (<1 psec)
78.47.D- Time resolved spectroscopy (>1 psec)
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors

High performance solution-deposited amorphous indium gallium zinc oxide thin film transistors by oxygen plasma treatment

Pradipta K. Nayak, M. N. Hedhili, Dongkyu Cha, and H. N. Alshareef

Appl. Phys. Lett. 100, 202106 (2012); http://dx.doi.org/10.1063/1.4718022 (4 pages) | Cited 3 times

Online Publication Date: 16 May 2012

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Solution-deposited amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) with high performance were fabricated using O2-plasma treatment of the films prior to high temperature annealing. The O2-plasma treatment resulted in a decrease in oxygen vacancy and residual hydrocarbon concentration in the a-IGZO films, as well as an improvement in the dielectric/channel interfacial roughness. As a result, the TFTs with O2-plasma treated a-IGZO channel layers showed three times higher linear field-effect mobility compared to the untreated a-IGZO over a range of processing temperatures. The O2-plasma treatment effectively reduces the required processing temperature of solution-deposited a-IGZO films to achieve the required performance.
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85.30.Tv Field effect devices
81.05.Gc Amorphous semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.40.Gh Other heat and thermomechanical treatments

Surface passivation of c-Si by atmospheric pressure chemical vapor deposition of Al2O3

Lachlan E. Black and Keith R. McIntosh

Appl. Phys. Lett. 100, 202107 (2012); http://dx.doi.org/10.1063/1.4718596 (5 pages)

Online Publication Date: 16 May 2012

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Atmospheric pressure chemical vapor deposition of Al2O3 is shown to provide excellent passivation of crystalline silicon surfaces. Surface passivation, permittivity, and refractive index are investigated before and after annealing for deposition temperatures between 330 and 520 °C. Deposition temperatures >440 °C result in the best passivation, due to both a large negative fixed charge density (∼2 × 1012 cm−2) and a relatively low interface defect density (∼1 × 1011 eV−1 cm−2), with or without an anneal. The influence of deposition temperature on film properties is found to persist after subsequent heat treatment. Correlations between surface passivation properties and the permittivity are discussed.
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81.65.Rv Passivation
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Study of temperature sensitive optical parameters and junction temperature determination of light-emitting diodes

Yue Lin, Yu-Lin Gao, Yi-Jun Lu, Li-Hong Zhu, Yong Zhang, and Zhong Chen

Appl. Phys. Lett. 100, 202108 (2012); http://dx.doi.org/10.1063/1.4718612 (4 pages) | Cited 2 times

Online Publication Date: 17 May 2012

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We investigate the current and temperature dependence of GaN-based high power blue light-emitting diodes and identify a set of temperature sensitive optical parameters (TSOPs) that can provide a real-time solution for determining the junction temperature (Tj). The relationships among Tj, forward current and TSOPs, “center of mass” wavelength, and, in particular, full width at half maximum (FWHM) have been studied, and the relevant mathematic models have been developed. The analysis indicates that using FWHM may yield higher accuracy than using other parameters as TSOPs.
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85.60.Jb Light-emitting devices

Control of supercurrent in a self-assembled InAs quantum dot Josephson junction by electrical tuning of level overlaps

Y. Kanai, R. S. Deacon, A. Oiwa, K. Yoshida, K. Shibata, K. Hirakawa, and S. Tarucha

Appl. Phys. Lett. 100, 202109 (2012); http://dx.doi.org/10.1063/1.4719072 (3 pages)

Online Publication Date: 17 May 2012

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We study supercurrent in a single InAs self-assembled quantum dot contacted with superconducting leads and demonstrate that for regions where energy level spacing and charging energy are smaller than tunnel coupling, the supercurrent may be controlled by the degree of overlaps between energy levels, which is tunable using a side-gate electrode. In such regions, we find strong correlation between the supercurrent and the normal state conductance when the device parameters are tuned. In a Kondo regime with low Kondo temperature, we find that the scaling of the supercurrent and normal state conductance varies when the side-gate voltage is changed.
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74.50.+r Tunneling phenomena; Josephson effects
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.fc Electric and thermal conductivity
73.63.Kv Quantum dots
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Effect of oxygen deficiency on room temperature ferromagnetism in Co doped ZnO

Hao Gu, Wen Zhang, Yongbing Xu, and Mi Yan

Appl. Phys. Lett. 100, 202401 (2012); http://dx.doi.org/10.1063/1.4717741 (4 pages) | Cited 6 times

Online Publication Date: 15 May 2012

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We investigated the correlation between magnetization and oxygen vacancies in Zn0.95Co0.05O nanoparticles. Enhanced magnetizations were found in SiO2 nanopowders and carbon nanotubes (CNTS) treated Zn0.95Co0.05O, which are attributed to minimizing nanoparticle size and increasing oxygen vacancy concentration. After oxygen annealing, the magnetization of both non-treated Zn0.95Co0.05O and CNTS treated Zn0.95Co0.05O decreased sharply with the filling of the oxygen vacancies, while the SiO2 treated Zn0.95Co0.05O was influenced little as the amorphous SiO2 shell prevents the diffusion of oxygen into magnetic particles. It demonstrated that the ferromagnetism comes from the interfacial oxygen deficiency and is tunable by changing the oxygen vacancies.
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81.05.Dz II-VI semiconductors
61.72.jd Vacancies
61.72.Cc Kinetics of defect formation and annealing
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effect of cold working in a magnetic field on the shape of a ferromagnetic nanocontact

Marc Müller, Richard Montbrun, Christoph Sürgers, and Hilbert v. Löhneysen

Appl. Phys. Lett. 100, 202402 (2012); http://dx.doi.org/10.1063/1.4718307 (5 pages)

Online Publication Date: 15 May 2012

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The role of a magnetic field present during formation of a ferromagnetic nanocontact—established by mechanically pulling a thin dysprosium wire—is investigated. We demonstrate that the shape of the nanocontact depends on the strength and direction of the magnetic field applied during plastic deformation of the contact. The different contact shapes obtained after cycles of tensile or compressive stress are attributed to the rearrangement of magnetic domains during formation of the nanocontact by magnetoelastic coupling.
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81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
75.50.Cc Other ferromagnetic metals and alloys
75.80.+q Magnetomechanical effects, magnetostriction
81.07.Lk Nanocontacts

Anomalies of magnetic properties and magnetovolume effect in Cd1−xMnxGeAs2 at hydrostatic pressure

A. Yu. Mollaev, I. K. Kamilov, R. K. Arslanov, T. R. Arslanov, U. Z. Zalibekov, V. M. Novotortsev, S. F. Marenkin, and V. M. Trukhan

Appl. Phys. Lett. 100, 202403 (2012); http://dx.doi.org/10.1063/1.4718419 (4 pages) | Cited 1 time

Online Publication Date: 15 May 2012

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We present the experimental results of the effect hydrostatic pressure up to P ≤ 7 GPa applied at the room temperatures in diluted magnetic semiconductor Cd1−xMnxGeAs2 (x = 0.06 − 0.3). We have found the pressure areas at which anomalies in magnetic properties were observed. Induced by hydrostatic pressure at P > 1.5 GPa magnetic phase transitions, interpreted as metamagnetic transition, were observed. The transitions from magnetic-ordered into magnetic disordered phases in region P > 4.1 GPa on the pressure dependences of relative volume compressibility were detected. We estimated the values of bulk modulus and volume magnetostriction. It is shown that high pressures significantly decrease the Curie temperature with values dTC/dP ≈ (−14.0 ÷ −6.8) K/GPa.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Pp Magnetic semiconductors
81.40.Lm Deformation, plasticity, and creep
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.80.+q Magnetomechanical effects, magnetostriction
81.40.Jj Elasticity and anelasticity, stress-strain relations

Reversibility in the inverse magnetocaloric effect in Mn3GaC studied by direct adiabatic temperature-change measurements

Ö. Çakιr and M. Acet

Appl. Phys. Lett. 100, 202404 (2012); http://dx.doi.org/10.1063/1.4717181 (3 pages) | Cited 3 times

Online Publication Date: 15 May 2012

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Thermal-hysteresis affects adversely the reversibility of the magnetocaloric effect around a first order magnetostructural transition. In Mn3GaC, a first order antiferromagnetic-ferromagnetic transition is accompanied by a volume-change and a 5 K thermal-hysteresis. We study the reversibility of the magnetocaloric effect in the transition region by direct adiabatic temperature-change measurements. The magnetic field is cycled between 0 and 3 T, and the temperature-change is observed. We find that the system exhibits a temperature-change of 3.1 K in the virgin state, and all subsequent cycling leads to a 2.8 K warming and cooling when the field is decreased and increased, respectively.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.78.-n Magnetization dynamics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Temperature and concentration-dependent relaxation of ferrofluids characterized with a high-Tc SQUID-based nuclear magnetic resonance spectrometer

Hong-Chang Yang, Chieh-Wen Liu, S. H. Liao, Hsin-Hsien Chen, M. J. Chen, K. L. Chen, Herng-Er Horng, S. Y. Yang, and L. M. Wang

Appl. Phys. Lett. 100, 202405 (2012); http://dx.doi.org/10.1063/1.4718032 (4 pages) | Cited 3 times

Online Publication Date: 16 May 2012

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We investigated the relaxation of protons in magnetic fluids using a high-Tc SQUID magnetometer. It was found that the longitudinal relaxation rate, 1/T1, is slower than the transverse relaxation rate, 1/T2, for ferrofluids in the same field. This is due to the fact that the 1/T1 process involves returning the magnetization to the z-direction, which automatically involves the loss of magnetization in the x-y plane governed by the 1/T2 process. Additionally, 1/T1 and 1/T2 at high temperatures are slower than the corresponding relaxation rates at low temperatures, which is due to the enhanced Brownian motion of nanoparticles at high temperatures.
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75.50.Mm Magnetic liquids
76.60.Es Relaxation effects
05.40.Jc Brownian motion

The study of perpendicular magnetic anisotropy in CoFeB sandwiched by MgO and tantalum layers using polarized neutron reflectometry

T. Zhu, Y. Yang, R. C. Yu, H. Ambaye, V. Lauter, and J. Q. Xiao

Appl. Phys. Lett. 100, 202406 (2012); http://dx.doi.org/10.1063/1.4718423 (4 pages) | Cited 3 times

Online Publication Date: 16 May 2012

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The perpendicular magnetic anisotropy (PMA) in CoFeB sandwiched by MgO and tantalum layers was investigated using anomalous Hall effect and polarized neutron reflectometry. It was found that a large PMA in the CoFeB above MgO layer was related to its low magnetization compared to the case of CoFeB under MgO layer. Using the sensitivity of neutrons to the absorption cross-section of boron, we unambiguously determined the depth profile of the boron distribution and showed that after annealing, most of the boron diffused to form a 2-nm-thick interface layer between the CoFeB and tantalum layers.
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75.30.Gw Magnetic anisotropy
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation
72.15.Gd Galvanomagnetic and other magnetotransport effects

Temperature dependence of carrier spin polarization determined from current-induced domain wall motion in a Co/Ni nanowire

K. Ueda, T. Koyama, R. Hiramatsu, D. Chiba, S. Fukami, H. Tanigawa, T. Suzuki, N. Ohshima, N. Ishiwata, Y. Nakatani, K. Kobayashi, and T. Ono

Appl. Phys. Lett. 100, 202407 (2012); http://dx.doi.org/10.1063/1.4718599 (3 pages) | Cited 2 times

Online Publication Date: 17 May 2012

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We have investigated the temperature dependence of the current-induced magnetic domain wall (DW) motion in a perpendicularly magnetized Co/Ni nanowire at various temperatures and with various applied currents. The carrier spin polarization was estimated from the measured domain wall velocity. We found that it decreased more with increasing temperature from 100 K to 530 K than the saturation magnetization did.
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81.05.Bx Metals, semimetals, and alloys
81.07.Gf Nanowires
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
75.50.Tt Fine-particle systems; nanocrystalline materials
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GaMnAs: Position of Mn-d levels and majority spin band gap predicted from GGA-1/2 calculations

R. R. Pelá, M. Marques, L. G. Ferreira, J. Furthmüller, and L. K. Teles

Appl. Phys. Lett. 100, 202408 (2012); http://dx.doi.org/10.1063/1.4718602 (4 pages) | Cited 2 times

Online Publication Date: 17 May 2012

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Among all magnetic semiconductors, GaMnAs seems to be the most important one. In this work, we present accurate first-principles calculations of GaMnAs within the GGA-1/2 approach: We concentrate our efforts in obtaining the position of the peak of Mn-d levels in the valence band and also the majority spin band gap. For the position of the Mn-d peak, we find a value of 3.3 eV below the Fermi level, in good agreement with the most recent experimental results of 3.5 and 3.7 eV. An analytical expression that fits the calculated Eg(x) for majority spin is derived in order to provide ready access to the band gap for the composition range from 0 to 0.25. We found a value of 3.9 eV for the gap bowing parameter. The results agree well with the most recent experimental data.
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71.20.Nr Semiconductor compounds
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
75.50.Pp Magnetic semiconductors

d carrier induced intrinsic room temperature ferromagnetism in Nb:TiO2 film

J. Y. Yang, Y. L. Han, L. He, R. F. Dou, C. M. Xiong, and J. C. Nie

Appl. Phys. Lett. 100, 202409 (2012); http://dx.doi.org/10.1063/1.4707378 (4 pages) | Cited 3 times

Online Publication Date: 17 May 2012

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High crystalline anatase TiO2 and Nb:TiO2 thin films were fabricated on LaAlO3 (100) substrates by pulsed laser deposition. Room temperature ferromagnetism was obtained in Nb:TiO2 but absent in pure TiO2. The Kondo effect and anomalous Hall effect observed in metallic Nb:TiO2 strongly confirmed the existence of exchange interaction between intrinsic local magnetic moments and carriers. High energy resolution x-ray photoelectron spectroscopy studies of the Nb:TiO2 thin film revealed clear signals of Ti3+ and Nb4+ ions, which had one unpaired d electron responsible for the local magnetic moments. This result consisted quite well with the spin polarized first principle calculation.
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72.25.-b Spin polarized transport
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Heating asymmetry induced by tunneling current flow in magnetic tunnel junctions

E. Gapihan, J. Hérault, R. C. Sousa, Y. Dahmane, B. Dieny, L. Vila, I. L. Prejbeanu, C. Ducruet, C. Portemont, K. Mackay, and J. P. Nozières

Appl. Phys. Lett. 100, 202410 (2012); http://dx.doi.org/10.1063/1.4719663 (4 pages) | Cited 2 times

Online Publication Date: 18 May 2012

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In this work, exchange bias was used as a probe to characterise the temperature profile induced by the inelastic relaxation of electrons tunnelling across a MgO barrier. Thermally assisted magnetic random access memory (TA-MRAM) cells comprising a magnetic tunnel junction (MTJ) with a reference pinned layer and a FeMn exchange biased storage layer were used. The pinning direction of the ferromagnetic storage layer is reversed when heated above the blocking temperature of the antiferromagnetic layer (FeMn). The power density required to reach this blocking temperature in the FeMn layer depends on the current polarity, indicating that the heat source term associated with the current flowing through the barrier depends itself on the current direction in contrast to simple Joule heating. This effect is due to the mechanism of energy dissipation in tunnelling. The tunnelling itself is ballistic i.e., without dissipation. However, after tunnelling, the hot electrons very quickly relax to the Fermi energy thereby loosing their excess energy in the receiving electrode. Therefore, the heat is essentially generated on one side of the barrier so that the whole profile of temperature throughout the pillar depends on the current direction. Full 3D thermal simulations also confirmed the temperature profile asymmetry. The proper choice of heating current direction (i.e., voltage polarity applied to the MTJ) can yield a reduction of about 10% in the heating power density required to enable writing in thermally assisted MRAM cells.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.23.Ad Ballistic transport
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
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