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3 Dec 2012

Volume 101, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 233101 (2012); http://dx.doi.org/10.1063/1.4749281 (3 pages)

S. A. Studenikin, J. Thorgrimson, G. C. Aers, A. Kam, P. Zawadzki, Z. R. Wasilewski, A. Bogan, and A. S. Sachrajda
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Inverse melting in stressed fused silica

Philippe Bouchut

Appl. Phys. Lett. 101, 231905 (2012); http://dx.doi.org/10.1063/1.4769357 (4 pages)

Online Publication Date: 5 December 2012

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The emissive properties of proton implanted fused silica surfaces have been studied by laser beam annealing. When submitted to a high thermal step from a focused CO2 laser, an intense near infra-red thermoluminescence peak rises at a heating rate threshold. The in plane tensile stress relaxes and silica melts. We show that in the irreversible inverse melting of stressed fused silica, the protons exo-diffuse through internal modes coupling. The heat and mass transfer is one entropy flux whose dynamics are regulated by the mass transport. Inverse melting is the thermodynamic process that initiates the glass transition when heating.
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64.70.dj Melting of specific substances
61.72.Cc Kinetics of defect formation and annealing
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
65.40.De Thermal expansion; thermomechanical effects
78.60.Kn Thermoluminescence

Mitigating residual stress in Cu metallization

Conal E. Murray, Jean Jordan-Sweet, E. Todd Ryan, and Michael F. Toney

Appl. Phys. Lett. 101, 231906 (2012); http://dx.doi.org/10.1063/1.4769366 (4 pages)

Online Publication Date: 5 December 2012

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The application of a cryogenic thermal excursion to passivated copper films has been demonstrated to dramatically reduce the magnitude of residual stress and to induce compressive, in-plane stress at room temperature. In-situ x-ray diffraction measurements reveal the evolution of in-plane stress within SiCxNyHz and TaN capped Cu films, which undergo significant plastic behavior on cooling and as the film approaches room temperature during heating. The resulting compressive stress represents a more favorable condition to mitigate voiding within the metallization. In-situ and ex-situ measurements of SiCxNyHz capped Cu films reveal that the final stress state is independent of cooling rate.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Microstructure and martensitic transformation in the Fe-Mn-Al-Ni shape memory alloy with B2-type coherent fine particles

T. Omori, M. Nagasako, M. Okano, K. Endo, and R. Kainuma

Appl. Phys. Lett. 101, 231907 (2012); http://dx.doi.org/10.1063/1.4769375 (4 pages)

Online Publication Date: 5 December 2012

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Microstructure and martensitic transformation yielding a magnetic change were investigated for Fe43.5Mn34Al15Ni7.5 alloy with B2-type fine precipitates. Thermoelastic martensitic transformation from the ferromagnetic parent phase to the weak magnetic martensite with a nano-twinned fcc structure was confirmed. High-angle annular dark-field scanning transmission electron microscopic observation revealed that a β particle of about 10 nm maintains coherency with the matrix martensite phase, even though distorted due to the martensitic transformation. The martensitic transformation temperatures decreased about 75 K by application of a magnetic field of 70 kOe and magnetic field-induced reverse martensitic transformation was confirmed.
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81.30.Kf Martensitic transformations
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
61.72.Mm Grain and twin boundaries
75.50.Bb Fe and its alloys

Thermal conductivity of nano-grained SrTiO3 thin films

Brian M. Foley, Harlan J. Brown-Shaklee, John C. Duda, Ramez Cheaito, Brady J. Gibbons, Doug Medlin, Jon F. Ihlefeld, and Patrick E. Hopkins

Appl. Phys. Lett. 101, 231908 (2012); http://dx.doi.org/10.1063/1.4769448 (4 pages) | Cited 2 times

Online Publication Date: 6 December 2012

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We measure the thermal conductivities of nano-grained strontium titanate (ng-SrTiO3) films deposited on sapphire substrates via time-domain thermoreflectance. The 170 nm thick oxide films of varying grain-size were prepared from a chemical solution deposition process. We find that the thermal conductivity of ng-SrTiO3 decreases with decreasing average grain size and attribute this to increased phonon scattering at grain boundaries. Our data are well described by a model that accounts for the spectral nature of anharmonic Umklapp scattering along with grain boundary scattering and scattering due to the film thickness.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
78.20.N- Thermo-optic effects
61.46.-w Structure of nanoscale materials
63.20.Ry Anharmonic lattice modes
63.20.kd Phonon-electron interactions
63.20.kg Phonon-phonon interactions

Evaluation on residual stress in Bi3.15(Eu0.7Nd0.15)Ti3O12 polycrystalline ferroelectric thin film by using the orientation average method

Y. Wei, H. B. Cheng, X. Y. Wang, and X. J. Zheng

Appl. Phys. Lett. 101, 231909 (2012); http://dx.doi.org/10.1063/1.4769811 (4 pages)

Online Publication Date: 6 December 2012

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We propose an orientation average method to evaluate residual stresses in polycrystalline thin films. Bi3.15(Eu0.7Nd0.15)Ti3O12 was used to verify our approach, with films prepared by metal organic decomposition at various annealing temperatures. The mechanical properties and microstructure were characterized by nanoindentation and X-ray diffraction. The thin film annealed at 600 °C has the largest residual compressive stress of 771 MPa among all thin films. The residual stresses are evaluated by the proposed method and traditional sin2ψ method, and the maximum distinction is less than 6.43%, demonstrating that the proposed method is reliable and convenient to evaluate residual stress in polycrystalline thin films.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.55.A- Nucleation and growth
77.55.fp Other ferroelectric films
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

Growth analysis of (Ag,Cu)InSe2 thin films via real time spectroscopic ellipsometry

S. A. Little, V. Ranjan, R. W. Collins, and S. Marsillac

Appl. Phys. Lett. 101, 231910 (2012); http://dx.doi.org/10.1063/1.4769902 (4 pages)

Online Publication Date: 7 December 2012

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In situ and ex situ characterization methods have been applied to investigate the properties of (Ag,Cu)InSe2 (ACIS) thin films. Data acquired from real time spectroscopic ellipsometry (RTSE) experiments were analyzed to extract the evolution of the nucleating, bulk, and surface roughness layer thicknesses. The evolution of these layer thicknesses suggests a transition from Volmer-Weber to Stranski-Krastanov type behavior when Cu is replaced by Ag. The complex dielectric functions of ACIS at both deposition and room temperature as a function of film composition were also extracted from the RTSE data, enabling parameterization of the alloy optical properties.
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68.55.ag Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Li Other semiconductors
81.05.Hd Other semiconductors
81.15.Cd Deposition by sputtering
68.35.bg Semiconductors

A visualization of threading dislocations formation and dynamics in mosaic growth of GaN-based light emitting diode epitaxial layers on (0001) sapphire

P. Ravadgar, R. H. Horng, and S. L. Ou

Appl. Phys. Lett. 101, 231911 (2012); http://dx.doi.org/10.1063/1.4769905 (5 pages)

Online Publication Date: 7 December 2012

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A clear visualization of the origin and characteristics of threading dislocations (TDs) of GaN-based light emitting diode epitaxial layers on (0001) sapphire substrates have been carried out. Special experimental set up and chemical etchant along with field emission scanning electron microscopy are employed to study the dynamics of GaN TDs at different growth stages. Cross-sectional transmission electron microscopy analysis visualized the formation of edge TDs is arising from extension of coalescences at boundaries of different tilting-twining nucleation grains “mosaic growth.” Etch pits as representatives of edge TDs are in agreement with previous theoretical models and analyses of TDs core position and characteristics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Mm Grain and twin boundaries
78.66.Fd III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
85.60.Jb Light-emitting devices
68.55.ag Semiconductors
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Polarization dependent optical control of atomic arrangement in multilayer Ge-Sb-Te phase change materials

Kotaro Makino, Junji Tominaga, Alexander V. Kolobov, Paul Fons, and Muneaki Hase

Appl. Phys. Lett. 101, 232101 (2012); http://dx.doi.org/10.1063/1.4768785 (4 pages)

Online Publication Date: 3 December 2012

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We report the optical perturbation of atomic arrangement in the layered in GeTe/Sb2Te3 phase change memory material. To observe the structural change, the coherent A1 mode of GeTe4 local structure was investigated at various polarization angles of femtosecond pump pulses with the fluence at ≤ 78 μJ/cm2. p-polarization found to be more effective in inducing the A1 frequency shift that can be either reversible or irreversible depending on the pump fluence. The predominant origin of this shift is attributed to rearrangement of Ge atoms driven by anisotropic dissociation of the Ge-Te bonds along the [111] axis after the p-polarized pulse irradiation.
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63.22.Np Layered systems
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.47.J- Ultrafast spectroscopy (<1 psec)

P-type behavior of Sb doped ZnO from p-n-p memory structure

Jian Huang, Zonglin Li, Sheng Chu, and Jianlin Liu

Appl. Phys. Lett. 101, 232102 (2012); http://dx.doi.org/10.1063/1.4769097 (4 pages)

Online Publication Date: 3 December 2012

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Antimony (Sb) doped p-type ZnO was studied by using Sb-ZnO/ZnO/Sb-ZnO p-n-p structure. Secondary ion mass spectrometry result confirmed the formation of the structure. Rectifying current-voltage characteristics between Sb-ZnO and undoped ZnO layers were achieved, proving the p-n junction was formed. The p-type behavior from the p-n-p structure was studied by using the capacitance-voltage measurement and small signal model. The voltage operation led to the charging/discharging of the structure, showing nonvolatile memory effect. Very long retention time was achieved. This research suggests that p-type ZnO can be evaluated by a p-n-p structure, which could be promising for future nonvolatile memory applications.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
84.30.Sk Pulse and digital circuits
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Electrically active Er doping in InAs, In0.53Ga0.47As, and GaAs

Peter G. Burke, Lars Ismer, Hong Lu, Elan Frantz, Anderson Janotti, Chris G. Van de Walle, John E. Bowers, and Arthur C. Gossard

Appl. Phys. Lett. 101, 232103 (2012); http://dx.doi.org/10.1063/1.4769248 (4 pages)

Online Publication Date: 4 December 2012

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The electron concentration in dilute alloys of Er in GaAs, In0.53Ga0.47As, and InAs grown by molecular beam epitaxy is studied as a function of Er concentration and In content. Using first-principles calculations based on hybrid density functional theory, we attribute an observed increase in conduction electron concentration to Er incorporation on interstitial sites. Er also incorporates on substitutional sites where it is isovalent and electrically inactive. The formation energy of interstitial Er in InAs is significantly smaller than in GaAs, allowing for more electrically active Er in InAs. The results provide insight into characteristics of rare-earth elements as dopants in semiconductors.
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61.72.uj III-V and II-VI semiconductors
68.55.ag Semiconductors
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.jj Interstitials

Correlated evolution of barrier capacitance charging, generation, and drift currents and of carrier lifetime in Si structures during 25 MeV neutrons irradiation

E. Gaubas, T. Ceponis, A. Jasiunas, A. Uleckas, J. Vaitkus, E. Cortina, and O. Militaru

Appl. Phys. Lett. 101, 232104 (2012); http://dx.doi.org/10.1063/1.4769370 (3 pages)

Online Publication Date: 4 December 2012

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The in situ examination of barrier capacitance charging, of generation and drift currents, and of carrier lifetime in Si structures during 25 MeV neutrons irradiation has been implemented to correlate radiation induced changes in carrier recombination, thermal release, and drift characteristics and to clarify their impact on detector performance. It has been shown that microwave probed photo-conductivity technique implemented in contact-less and distant manner can be a powerful tool for examination in wide dynamic range of carrier lifetime modified by radiation defects and for rather precise prediction of detector performance.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
85.60.Gz Photodetectors (including infrared and CCD detectors)
61.80.Hg Neutron radiation effects
61.82.Fk Semiconductors

Observation of momentum space semi-localization in Si-doped β-Ga2O3

P. Richard, T. Sato, S. Souma, K. Nakayama, H. W. Liu, K. Iwaya, T. Hitosugi, H. Aida, H. Ding, and T. Takahashi

Appl. Phys. Lett. 101, 232105 (2012); http://dx.doi.org/10.1063/1.4769109 (5 pages)

Online Publication Date: 4 December 2012

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We performed an angle-resolved photoemission spectroscopy study of Si-doped β-Ga2O3. We observed very small photoemission intensity near the Fermi level corresponding to non-dispersive states assigned to Si impurities. We show evidence for a quantization of these states that is accompanied by a confinement in the momentum space consistent with a real-space finite confinement observed in a previous scanning tunneling microscopy study. Our results suggest that this semi-localization in the conjugate spaces plays a crucial role in the electronic conduction of this material.
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71.20.Nr Semiconductor compounds
71.55.Ht Other nonmetals
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Fish scale terrace GaInN/GaN light-emitting diodes with enhanced light extraction

Christoph J. M. Stark, Theeradetch Detchprohm, Liang Zhao, Tanya Paskova, Edward A. Preble, and Christian Wetzel

Appl. Phys. Lett. 101, 232106 (2012); http://dx.doi.org/10.1063/1.4769442 (4 pages)

Online Publication Date: 5 December 2012

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Non-planar GaInN/GaN light-emitting diodes were epitaxially grown to exhibit steps for enhanced light emission. By means of a large off-cut of the epitaxial growth plane from the c-plane (0.06° to 2.24°), surface morphologies of steps and inclined terraces that resemble fish scale patterns could controllably be achieved. These patterns penetrate the active region without deteriorating the electrical device performance. We find conditions leading to a large increase in light-output power over the virtually on-axis device and over planar sapphire references. The process is found suitable to enhance light extraction even without post-growth processing.
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85.60.Jb Light-emitting devices

Formation of arsenolite crystals at room temperature after very high dose arsenic implantation in silicon

Florian Meirer, Damiano Giubertoni, Evgeny Demenev, Lia Vanzetti, Salvatore Gennaro, Michele Fedrizzi, Giancarlo Pepponi, Apurva Mehta, Piero Pianetta, Georg Steinhauser, Vinayak Vishwanath, Majeed Foad, and Massimo Bersani

Appl. Phys. Lett. 101, 232107 (2012); http://dx.doi.org/10.1063/1.4769446 (4 pages)

Online Publication Date: 5 December 2012

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Spontaneous growth of arsenolite micro-crystals at room temperature after high fluence, low energy arsenic trihydride implantation in silicon was observed on the wafer surface after exposure to air. The crystals have been identified unambiguously by x-ray absorption and fluorescence spectroscopy. Thermal treatment easily sublimates the crystals at temperatures as low as 200 °C without any relevant in-diffusion of As into the substrate. The deposition of a thin As-rich layer under high fluence implantation conditions is suggested as possible precursor for crystal formation. The same layer can explain the anomalous retained dose increase often observed after annealing.
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61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
78.55.Ap Elemental semiconductors
78.70.Dm X-ray absorption spectra
81.05.Cy Elemental semiconductors

Room-temperature method for minimizing light-induced degradation in crystalline silicon

J. Lindroos, M. Yli-Koski, A. Haarahiltunen, and H. Savin

Appl. Phys. Lett. 101, 232108 (2012); http://dx.doi.org/10.1063/1.4769809 (3 pages) | Cited 1 time

Online Publication Date: 6 December 2012

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Although light-induced degradation (LID) in crystalline silicon is attributed to the formation of boron-oxygen recombination centers, copper contamination of silicon has recently been observed to result in similar degradation. As positively charged interstitial copper stays mobile at room temperature in silicon, we show that the bulk copper concentration can be reduced by depositing a large negative charge onto the wafer surface. Consequently, light-induced degradation is reduced significantly in both low- and high-resistivity boron-doped Czochralski-grown silicon.
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81.10.Fq Growth from melts; zone melting and refining
61.72.jj Interstitials
61.72.uf Ge and Si

Atomic layer deposition of Sc2O3 for passivating AlGaN/GaN high electron mobility transistor devices

Xinwei Wang, Omair I. Saadat, Bin Xi, Xiabing Lou, Richard J. Molnar, Tomás Palacios, and Roy G. Gordon

Appl. Phys. Lett. 101, 232109 (2012); http://dx.doi.org/10.1063/1.4770071 (4 pages) | Cited 1 time

Online Publication Date: 7 December 2012

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Polycrystalline, partially epitaxial Sc2O3 films were grown on AlGaN/GaN substrates by atomic layer deposition (ALD). With this ALD Sc2O3 film as the insulator layer, the Sc2O3/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors showed excellent electrical performance with a high Ion/Ioff ratio of over 108 and a low subthreshold slope of 75 mV/dec. The UV/NH4OH surface treatment on AlGaN/GaN prior to ALD was found to be critical for achieving these excellent figures. In addition, the Sc2O3 dielectric is found to be negatively charged, which facilitates the enhancement-mode operation. While bare Sc2O3 suffers from moisture degradation, depositing a moisture blocking layer of ALD Al2O3 can effectively eliminate this effect.
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85.30.Tv Field effect devices
81.65.Rv Passivation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
73.61.Ng Insulators
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Magnetotransport properties of dual MgO barrier magnetic tunnel junctions consisting of CoFeB/FeNiSiB/CoFeB free layers

D. K. Kim, J. U. Cho, B. S. Chun, K. H. Shin, K. J. Lee, M. Tsunoda, M. Takahashi, and Y. K. Kim

Appl. Phys. Lett. 101, 232401 (2012); http://dx.doi.org/10.1063/1.4768931 (4 pages)

Online Publication Date: 3 December 2012

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We report the transport properties of a dual MgO barrier magnetic tunnel junction (DMTJ) where a FeNiSiB layer was inserted in a CoFeB free layer. Upon post-deposition annealing at 330 °C, the tunneling magnetoresistance (TMR) ratio of the DMTJ with a hybrid CoFeB/FeNiSiB/CoFeB free layer reached 195% which is higher than the TMR ratio of 121% from the DMTJ with the single CoFeB free layer. The bias voltage dependence profile was more symmetric for the hybrid case. Boron depth profiling result suggests that the FeNiSiB layer dragged boron atoms more to it rather than letting them diffuse toward CoFeB/MgO interfaces, resulting in improved MTJ performances.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments

Exchange-biased magnetic tunnel junctions with antiferromagnetic ε-Mn3Ga

H. Kurt, K. Rode, H. Tokuc, P. Stamenov, M. Venkatesan, and J. M. D. Coey

Appl. Phys. Lett. 101, 232402 (2012); http://dx.doi.org/10.1063/1.4768941 (4 pages)

Online Publication Date: 3 December 2012

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Oriented c-axis films of the hexagonal triangular antiferromagnetic ε-Mn3Ga have been used in bottom-pinned synthetic antiferromagnet magnetic tunnel junctions with MgO barriers, which show up to 150% tunneling magnetoresistance at room temperature. Exchange bias fields as high as 150 mT can be achieved for samples field-cooled from 100 °C. Thin films of the antiferromagnet have a Néel temperature in excess of 650 K and provide an interface exchange energy with CoFe of 0.09 mJ m−2. They show an isotropic uncompensated magnetization of Ms = 48 kA m−1, with a coercivity μ0Hc > 3 T.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Depth-selective electronic and magnetic properties of a Co2MnSi tunnel magneto-resistance electrode at a MgO tunnel barrier

B. Krumme, D. Ebke, C. Weis, S. I. Makarov, A. Warland, A. Hütten, and H. Wende

Appl. Phys. Lett. 101, 232403 (2012); http://dx.doi.org/10.1063/1.4769180 (4 pages)

Online Publication Date: 3 December 2012

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We investigated the electronic structure as well as the magnetic properties of a Co2MnSi film on MgO(100) element-specifically at the interface to a MgO tunnel barrier by means of X-ray absorption spectroscopy and X-ray magnetic circular dichroism. The electronic structure of the Co atoms as a function of the capping layer thickness remained unchanged, whereas the XA spectra of Mn indicate an increase of the unoccupied d states. The experimental findings are consistent with the interfacial structure proposed in the work by B. Hülsen et al. [Phys. Rev. Lett. 103, 046802 (2009)], where a MnSi layer is present at the interface to the MgO with oxygen atoms at top positions in the first MgO layer.
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75.47.Pq Other materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
72.20.My Galvanomagnetic and other magnetotransport effects

Effect of the magnetic domain structure in the ferromagnetic contact on spin accumulation in silicon

Y. Ando, S. Yamada, K. Kasahara, K. Sawano, M. Miyao, and K. Hamaya

Appl. Phys. Lett. 101, 232404 (2012); http://dx.doi.org/10.1063/1.4769221 (4 pages) | Cited 1 time

Online Publication Date: 4 December 2012

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We show a marked effect of magnetic domain structure in an epitaxial CoFe contact on spin accumulation signals in Si devices detected by three-terminal Hanle effect measurements. Experimental results indicate that magnetic domain structures cause large discrepancies in the estimation of spin lifetime and bias-current dependence of the spin accumulation signal. By introducing the domain walls in CoFe contact, spin accumulation signals are reduced, which is caused by the lateral spin transport in the Si channel. Thus, to understand precisely the physical properties of Si spintronic devices, it is important to take into account the control of magnetic domain structure in the contacts.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.76.+j Spin transport effects
72.25.Mk Spin transport through interfaces
75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Asymmetric hysteresis loops and its dependence on magnetic anisotropy in exchange biased Co/CoO core-shell nanoparticles

Sayan Chandra, Hafsa Khurshid, Manh-Huong Phan, and Hariharan Srikanth

Appl. Phys. Lett. 101, 232405 (2012); http://dx.doi.org/10.1063/1.4769350 (5 pages)

Online Publication Date: 4 December 2012

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The origin of asymmetry in field cooled (FC) hysteresis loops exhibiting exchange bias (EB) is investigated by studying the static and dynamic magnetic properties of core-shell Co/CoO nanoparticles. Two distinct freezing temperatures coresponding to the core (Tf-cr ∼ 190 K) and the shell moments (Tf-sh ∼ 95 K) are obtained from the energy barrier distribution. The FC loops are symmetric in the temperature range Tf-sh ≤ T ≤ Tf-cr, however, asymmetry in hysteresis is observed immediately below Tf-sh. These intriguing features are also probed by radio frequency transverse susceptibility (TS) experiments. We show that the first anisotropy fields obtained from the demagnetization and return curves of field cooled TS measurement, shift along the negative field axis and strikingly resemble the temperature dependence of EB. Field cooled TS measurements reveal the effect of competing Zeeman and anisotropy energy above and below Tf-sh to account for the development of asymmetry. Our study indicates that asymmetry in FC hysteresis loops is intrinsic to core-shell nanoparticles and develops only below the freezing temperature of the shell due to enhanced magnetic anisotropy.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.Jn Dynamics of magnetic nanoparticles
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.30.Sg Magnetocaloric effect, magnetic cooling

Microwave reflection imaging using a magnetic tunnel junction based spintronic microwave sensor

L. Fu, Z. X. Cao, S. Hemour, K. Wu, D. Houssameddine, W. Lu, S. Pistorius, Y. S. Gui, and C.-M. Hu

Appl. Phys. Lett. 101, 232406 (2012); http://dx.doi.org/10.1063/1.4769837 (4 pages) | Cited 1 time

Online Publication Date: 5 December 2012

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A far-field microwave imaging technique has been developed using a spintronic sensor based on a magnetic tunnel junction (MTJ). Such a sensor can directly rectify a microwave field into a dc voltage signal using the Seebeck effect. Thanks to the high conversion efficiency of the microwave rectification in MTJs, the microwave power sensitivity of the spintronic sensor is on the order of 1–10 mV/mW. This high sensitivity allows the sensor to directly measure the coherent spatial scattered microwave field distribution, which gives it the ability to non-destructively detect hidden objects down to a few wavelengths in size.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
07.55.-w Magnetic instruments and components

Room-temperature ferromagnetism induced and controlled by electric field in BaNbO3 films

Ensi Cao, Hongwei Qin, Yongjia Zhang, and Jifan Hu

Appl. Phys. Lett. 101, 232407 (2012); http://dx.doi.org/10.1063/1.4769901 (4 pages)

Online Publication Date: 6 December 2012

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The application of electric field can induce the room-temperature ferromagnetism (FM) in paramagnetic BaNbO3 films on the conductive Nb:SrTiO3 substrate. The electric field-induced ferromagnetism in BaNbO3 is connected with the hybridization between electrons of Nb-4d1 and the injected electrons from the conductive substrate, possibly leading to large density of states at the Fermi level and satisfying the Stoner criterion for ferromagnetism. By application of electric field in forward and reversed directions, the magnetization of electric field-induced FM can be adjusted in some extent. The application of electric field can also enhance the oxygen vacancies-induced room-temperature ferromagnetism in BaNbO3 films.
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75.70.Ak Magnetic properties of monolayers and thin films
61.72.jd Vacancies
71.20.Ps Other inorganic compounds
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Abnormal substrate temperature dependent out-of-plane anisotropy in FeCoNbB amorphous films

Youxing Yu, Youran Yang, Yijiao Shan, and Xiaofang Bi

Appl. Phys. Lett. 101, 232408 (2012); http://dx.doi.org/10.1063/1.4767952 (4 pages)

Online Publication Date: 7 December 2012

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Out-of-plane magnetic anisotropy (OMA) of FeCoNbB amorphous films has been studied. The OMA is abnormally enhanced by elevating the substrate temperature from room-temperature to 500 °C, being much different from most soft-magnetic amorphous films. Furthermore, the films show a slightly decay in the OMA when annealed at a temperature lower than the respective deposition temperature. But when annealed at a temperature 50 °C higher than the respective deposition temperature, the OMA suddenly disappears. Such results indicate a distinguishing mechanism of non-magnetoelastic-anisotropy dominated OMA. A model of co-effects of magnetoelastic anisotropy and microshape anisotropy is proposed.
Show PACS
75.30.Gw Magnetic anisotropy
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.15.Cd Deposition by sputtering
68.55.at Other materials
75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
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4-fold enhancement in the critical current density of YBa2Cu3O7 films by practical ion irradiation

H. Matsui, H. Ogiso, H. Yamasaki, T. Kumagai, M. Sohma, I. Yamaguchi, and T. Manabe

Appl. Phys. Lett. 101, 232601 (2012); http://dx.doi.org/10.1063/1.4769836 (4 pages)

Online Publication Date: 4 December 2012

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We report an up-to-4-fold enhancement in the in-magnetic-field critical current density at 77 K of epitaxial YBa2Cu3O7 films on CeO2-buffered SrTiO3 substrates by 3-MeV Au2+ irradiation. This indicates that irradiation using an industrially practical ion beam, which generally has kinetic energy less than 5 MeV, can provide a substantial increase in the in-field current performance of high-temperature superconductor films. Transmission electron microscopy results show that point-like defects smaller than 6 nm in diameter were created in the films by the irradiation.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
61.72.J- Point defects and defect clusters
61.80.Jh Ion radiation effects
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