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3 Sep 2012

Volume 101, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 103101 (2012); http://dx.doi.org/10.1063/1.4748099 (5 pages)

Massimo Cuscunà, Annalisa Convertino, Emiliano Zampetti, Antonella Macagnano, Alessandro Pecora, Guglielmo Fortunato, Laura Felisari, Giuseppe Nicotra, Corrado Spinella, and Faustino Martelli
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Evidence for ferromagnetic strain glass in Ni-Co-Mn-Ga Heusler alloy system

Yu Wang, Chonghui Huang, Jinghui Gao, Sen Yang, Xiangdong Ding, Xiaoping Song, and Xiaobing Ren

Appl. Phys. Lett. 101, 101913 (2012); http://dx.doi.org/10.1063/1.4751250 (4 pages) | Cited 1 time

Online Publication Date: 7 September 2012

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We report that both a strain glass transition and a ferromagnetic transition take place in a Ni43Co12Mn20Ga25 Heusler alloy. This results in a ferromagnetic strain glass with coexisting short range strain ordering and long range magnetic moment ordering. The phase diagram of the Ni-Co-Mn-Ga system shows that the substitutional point defect Co in the Ni-site plays the following roles: (i) suppressing the long range strain ordering of martensite, (ii) promoting local strain ordering of strain glass by producing random local stresses, and (iii) enhancing the ferromagnetic exchange interaction, which leads to the formation of ferromagnetic strain glass.
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64.70.pe Metallic glasses
75.50.Cc Other ferromagnetic metals and alloys
75.30.Cr Saturation moments and magnetic susceptibilities
81.30.Bx Phase diagrams of metals, alloys, and oxides
75.30.Et Exchange and superexchange interactions
61.72.J- Point defects and defect clusters
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Stable highly conductive ZnO via reduction of Zn vacancies

D. C. Look, T. C. Droubay, and S. A. Chambers

Appl. Phys. Lett. 101, 102101 (2012); http://dx.doi.org/10.1063/1.4748869 (3 pages) | Cited 3 times

Online Publication Date: 4 September 2012

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Growth of Ga-doped ZnO by pulsed laser deposition at 200 °C in an ambient of Ar and H2 produces a resistivity of 1.5 × 10−4 Ω-cm, stable to 500 °C. The resistivity can be further reduced to 1.2 × 10−4 Ω-cm by annealing on Zn foil, which reduces the compensating Zn-vacancy acceptor concentration NA to 5 × 1019 cm−3, only 3% of the Ga-donor concentration ND of 1.6 × 1021 cm−3, with ND and NA determined from a degenerate mobility theory. The plasmon-resonance wavelength is only 1060 nm, further bridging the gap between metals and semiconductors.
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81.15.Fg Pulsed laser ablation deposition
61.72.jd Vacancies
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
68.55.ag Semiconductors
61.72.Cc Kinetics of defect formation and annealing

The role of structural properties on deep defect states in Cu2ZnSnS4 studied by photoluminescence spectroscopy

M. Grossberg, J. Krustok, J. Raudoja, and T. Raadik

Appl. Phys. Lett. 101, 102102 (2012); http://dx.doi.org/10.1063/1.4750249 (4 pages) | Cited 3 times

Online Publication Date: 4 September 2012

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In this study, we investigated the photoluminescence (PL) properties of Cu2ZnSnS4 polycrystals. Two PL bands at 1.27 eV and 1.35 eV at T = 10 K were detected. Similar behaviour with temperature and excitation power was found for both PL bands and attributed to the band-to-impurity recombination. Interestingly, the thermal activation energies determined from the temperature dependence of the PL bands coincide. With the support of the Raman results, we propose that the observed PL bands arise from the band-to-impurity-recombination process involving the same deep acceptor defect with ionization energy of around 280 meV but different Cu2ZnSnS4 phase with different bandgap energy.
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61.66.Fn Inorganic compounds
71.20.Nr Semiconductor compounds
71.55.Ht Other nonmetals
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials

Magnetism in MoS2 induced by proton irradiation

S. Mathew, K. Gopinadhan, T. K. Chan, X. J. Yu, D. Zhan, L. Cao, A. Rusydi, M. B. H. Breese, S. Dhar, Z. X. Shen, T. Venkatesan, and John T. L. Thong

Appl. Phys. Lett. 101, 102103 (2012); http://dx.doi.org/10.1063/1.4750237 (5 pages) | Cited 2 times

Online Publication Date: 5 September 2012

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Molybdenum disulphide, a diamagnetic layered dichalcogenide solid, is found to show magnetic ordering at room temperature when exposed to a 2 MeV proton beam. The temperature dependence of magnetization displays ferrimagnetic behavior with a Curie temperature of 895 K. A disorder mode corresponding to a zone-edge phonon and a Mo valence higher than +4 has been detected in the irradiated samples using Raman and x-ray photoelectron spectroscopy, respectively. The possible origins of long-range magnetic ordering in irradiated MoS2 samples are discussed.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.30.Hv Other nonmetallic inorganics
61.80.Jh Ion radiation effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics

Improvement of near-infrared absorption linewidth in AlGaN/GaN superlattices by optimization of delta-doping location

C. Edmunds, L. Tang, J. Shao, D. Li, M. Cervantes, G. Gardner, D. N. Zakharov, M. J. Manfra, and O. Malis

Appl. Phys. Lett. 101, 102104 (2012); http://dx.doi.org/10.1063/1.4751040 (4 pages)

Online Publication Date: 5 September 2012

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We report a systematic study of the near-infrared intersubband absorption in AlGaN/GaN superlattices grown by plasma-assisted molecular-beam epitaxy as a function of Si-doping profile with and without δ-doping. The transition energies are in agreement with theoretical calculations including many-body effects. A dramatic reduction of the intersubband absorption linewidth is observed when the δ-doping is placed at the end of the quantum well. This reduction is attributed to the improvement of interface roughness. The linewidth dependence on interface roughness is well reproduced by a model that considers the distribution of well widths measured with transmission electron microscopy.
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78.30.Fs III-V and II-VI semiconductors
68.65.Cd Superlattices
78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Electronic properties of crystalline Ge1-xSbxTey thin films

Roberto Fallica, Flavio Volpe, Massimo Longo, Claudia Wiemer, Olivier Salicio, and Adulfas Abrutis

Appl. Phys. Lett. 101, 102105 (2012); http://dx.doi.org/10.1063/1.4749839 (4 pages)

Online Publication Date: 6 September 2012

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Ge1-xSbxTey thin films, grown by metalorganic and hot-wire liquid injection chemical vapor deposition in different crystalline phases, are investigated to determine resistivity, carrier density, and carrier mobility in the 4.2–300 K temperature range. It is found that all these chalcogenides exhibit p-type conduction, high carrier density (>2 · 1020 cm−3), and no carrier freeze-out, regardless of composition. Low-temperature mobility data show that both chemical composition and growth technique affect the defect density and, in turn, the carrier scattering mechanisms. In this regard, charge carrier mobility is analyzed according to semi-empirical scattering models and an interpretation is provided.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
73.61.Jc Amorphous semiconductors; glasses
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.-d Chemical analysis and related physical methods of analysis
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Effects of growth temperature on Mg-doped GaN grown by ammonia molecular beam epitaxy

Christophe A. Hurni, Jordan R. Lang, Peter G. Burke, and James S. Speck

Appl. Phys. Lett. 101, 102106 (2012); http://dx.doi.org/10.1063/1.4751108 (4 pages) | Cited 1 time

Online Publication Date: 6 September 2012

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The hole concentration p in Mg-doped GaN films grown by ammonia molecular beam epitaxy depends strongly on the growth temperature TGR. At TGR = 760 °C, GaN:Mg films showed a hole concentration of p = 1.2 × 1018 cm−3 for [Mg] = 4.5×1019 cm−3, while at TGR = 840 °C, p = 4.4×1016 cm−3 for [Mg] = 7×1019 cm−3. Post-growth annealing did not increase p. The sample grown at 760 °C exhibited a low resistivity of 0.7 Ωcm. The mobility for all the samples was around 3−7 cm2/V s. Temperature-dependent Hall measurements and secondary ion mass spectroscopy suggest that the samples grown at TGR>760 °C are compensated by an intrinsic donor rather than hydrogen.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
61.72.Cc Kinetics of defect formation and annealing
73.61.Ey III-V semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
72.20.My Galvanomagnetic and other magnetotransport effects

Mg acceptor doping of In2O3 and overcompensation by oxygen vacancies

Oliver Bierwagen and James S. Speck

Appl. Phys. Lett. 101, 102107 (2012); http://dx.doi.org/10.1063/1.4751854 (4 pages) | Cited 2 times

Online Publication Date: 7 September 2012

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Mg-doped indium oxide (In2O3) thin films were grown by plasma-assisted molecular beam epitaxy with Mg-concentrations ranging from 1017 to 6×1020 cm−3. In this concentration range Mg was incorporated into In2O3 without discernable impediment nor formation of secondary phases. Despite the role of Mg as acceptor, the films were n-type conductive in the as-grown state or after annealing in vacuum. For Mg-concentrations well in excess of the unintentional donor concentration annealing in oxygen resulted in semi-insulating films without detectable p-type conductivity. These results strongly suggest oxygen vacancies to act as shallow donors in In2O3 that can overcompensate the Mg acceptors.
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61.72.up Other materials
68.55.aj Insulators
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.jd Vacancies
73.61.Ng Insulators
81.40.Gh Other heat and thermomechanical treatments
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Observation of a 0.5 conductance plateau in asymmetrically biased GaAs quantum point contact

N. Bhandari, P. P. Das, M. Cahay, R. S. Newrock, and S. T. Herbert

Appl. Phys. Lett. 101, 102401 (2012); http://dx.doi.org/10.1063/1.4749817 (4 pages) | Cited 4 times

Online Publication Date: 4 September 2012

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We report the observation of a robust anomalous conductance plateau near G = 0.5 G0 (G0 = 2e2/h) in asymmetrically biased AlGaAs/GaAs quantum point contacts (QPCs), with in-plane side gates in the presence of lateral spin-orbit coupling. This is interpreted as evidence of spin polarization in the narrow portion of the QPC. The appearance and evolution of the conductance anomaly has been studied at T = 4.2 K as a function of the potential asymmetry between the side gates. Because GaAs is a material with established processing techniques, high mobility, and a relatively high spin coherence length, the observation of spontaneous spin polarization in a side-gated GaAs QPC could eventually lead to the realization of an all-electric spin-valve at tens of degrees Kelvin.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.25.-b Spin polarized transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Unusual lattice constant changes and tunable magnetic moment compensation in Mn50−xCo25Ga25+x alloys

G. J. Li, E. K. Liu, H. G. Zhang, J. F. Qian, H. W. Zhang, J. L. Chen, W. H. Wang, and G. H. Wu

Appl. Phys. Lett. 101, 102402 (2012); http://dx.doi.org/10.1063/1.4749837 (4 pages) | Cited 2 times

Online Publication Date: 4 September 2012

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We report on unusual lattice parameter changes and tunable magnetic moment compensation in Mn50−xCo25Ga25+x (x = 0-25) Heusler alloys by substituting Ga for Mn. The observed lattice parameter first increases with increasing Ga content x, showing a maximum at x = 12.5, and then abnormally decreases due to the enhanced covalence effect between transition-metal and main-group atoms. Moreover, a tunable magnetic moment compensation was also observed due to the diversification in role of the main magnetic contributor when the structure varies from Hg2CuTi-type Mn2CoGa to Cu2MnAl-type CoMnGa2. These results provide an alternative way to simultaneously tune both the structural and magnetic properties of Heusler alloys, which is particularly important for developing flexible spintronics devices.
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61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

The magnetic Y-branch nanojunction: Domain-wall structure and magneto-resistance

Z. Chen, T.-Y. Lin, X. Wei, M. Matsunaga, T. Doi, Y. Ochiai, N. Aoki, and J. P. Bird

Appl. Phys. Lett. 101, 102403 (2012); http://dx.doi.org/10.1063/1.4750240 (5 pages)

Online Publication Date: 4 September 2012

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We analyze the domain structure of magnetic Y-branch nanojunctions that are formed by the intersection of a pair of orthogonal nanoscale notches. Dependent upon the magnetization history, we show the possibility of localizing various domain-wall (DW) structures at different parts of these junctions, leading to measurable magneto-resistance changes. These changes in turn allow the investigation of DW resistance, separate from the complicating effects of anisotropic magneto-resistance. The capacity to electrically detect the presence of DW structures in different regions of the junction may eventually make these structures of interest for future investigations of DW-enabled logic.
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75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms
75.75.Fk Domain structures in nanoparticles
75.47.-m Magnetotransport phenomena; materials for magnetotransport
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C60-based hot-electron magnetic tunnel transistor

M. Gobbi, A. Bedoya-Pinto, F. Golmar, R. Llopis, F. Casanova, and L. E. Hueso

Appl. Phys. Lett. 101, 102404 (2012); http://dx.doi.org/10.1063/1.4751030 (4 pages) | Cited 1 time

Online Publication Date: 4 September 2012

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A C60-based magnetic tunnel transistor is presented. The device is based on the collection of spin-filtered hot-electrons at a metal/C60 interface, and it allows an accurate measurement of the energy level alignment at such interface. A 89% change in the collected current under the application of a magnetic field demonstrates that these devices can be used as sensitive magnetic field sensors compatible with soft electronics.
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85.30.Tv Field effect devices

The spin-filter capability and spin-reversal effect of multidecker iron-borazine sandwich cluster

Zhi Yang, Shaoding Liu, Xuguang Liu, Yongzhen Yang, Xiuyan Li, Shijie Xiong, and Bingshe Xu

Appl. Phys. Lett. 101, 102405 (2012); http://dx.doi.org/10.1063/1.4751340 (4 pages)

Online Publication Date: 5 September 2012

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Using density functional theory and non-equilibrium Green's function technique, we performed theoretical investigations on the magnetic and transport properties of Fen(B3N3H6)n+1 (n = 1-4) sandwich clusters. The calculated results show that the clusters possess high magnetic moments owing to the unpaired dδ electrons. Furthermore, high spin-filter capability, negative differential resistance, and spin-reversal effect were found in the systems, and the possible physical origination of the phenomena was suggested. Our findings also indicate that the magnetic or electrical properties of the system could be controlled by cluster size, and these sandwich clusters are promising materials for application in molecular electronics or spintronics.
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73.40.Rw Metal-insulator-metal structures
75.30.Cr Saturation moments and magnetic susceptibilities

Pulse voltage-induced dynamic magnetization switching in magnetic tunneling junctions with high resistance-area product

Yoichi Shiota, Shinji Miwa, Takayuki Nozaki, Frédéric Bonell, Norikazu Mizuochi, Teruya Shinjo, Hitoshi Kubota, Shinji Yuasa, and Yoshishige Suzuki

Appl. Phys. Lett. 101, 102406 (2012); http://dx.doi.org/10.1063/1.4751035 (4 pages) | Cited 2 times

Online Publication Date: 5 September 2012

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We investigated pulse voltage-induced dynamic magnetization switchings in magnetic tunneling junctions with a high resistance-area product of 2 kΩ μm2. We found that bistable switching and the oscillatory behavior of switching probability as a function of voltage pulse duration are realized at a lower current density (−1.1 × 105 A/cm2) than in conventional spin-transfer-torque-induced magnetization switching. In addition, the switching probability at different voltage pulse strengths confirmed the existence of a voltage torque induced by a change in perpendicular magnetic anisotropy. This voltage-induced magnetization switching can be a useful technique in future spintronics devices with fast and highly reliable writing processes.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.78.Jp Ultrafast magnetization dynamics and switching

Excellent magnetocaloric properties of melt-extracted Gd-based amorphous microwires

N. S. Bingham, H. Wang, F. Qin, H. X. Peng, J. F. Sun, V. Franco, H. Srikanth, and M. H. Phan

Appl. Phys. Lett. 101, 102407 (2012); http://dx.doi.org/10.1063/1.4751038 (5 pages)

Online Publication Date: 6 September 2012

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We report upon the excellent magnetocaloric properties of Gd53Al24Co20Zr3 amorphous microwires. In addition to obtaining the large magnetic entropy change (−ΔSM ∼ 10.3 J/kg K at TC ∼ 95 K), an extremely large value of refrigerant capacity (RC ∼ 733.4 J/kg) has been achieved for a field change of 5 T in an array of forty microwires arranged in parallel. This value of RC is about 79% and 103% larger than those of Gd (∼410 J/kg) and Gd5Si2Ge1.9Fe0.1 (∼360 J/kg) regardless of their magnetic ordering temperatures. The design and fabrication of a magnetic bed made of these parallel-arranged microwires would thus be a very promising approach for active magnetic refrigeration for nitrogen liquefaction. Since these microwires can easily be assembled as laminate structures, they have potential applications as a cooling device for micro electro mechanical systems and nano electro mechanical systems.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.05.Bx Metals, semimetals, and alloys
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Giant induced magnetic anisotropy In strain annealed Co-based nanocomposite alloys

Samuel J. Kernion, Paul. R. Ohodnicki, Jr., Jane Grossmann, Alex Leary, Shen Shen, Vladimir Keylin, Joseph F. Huth, John Horwath, Matthew S. Lucas, and Michael E. McHenry

Appl. Phys. Lett. 101, 102408 (2012); http://dx.doi.org/10.1063/1.4751253 (5 pages) | Cited 3 times

Online Publication Date: 6 September 2012

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Low loss switching of soft magnetic materials at high frequencies benefits from tuning the induced anisotropy. We show induced anisotropies, Ku, as large as 1.89×104 J/m3, developed by strain annealing of Co-rich nanocomposite alloys. Crystalline phases in this alloy system have large negative magnetostrictive coefficients, leading to anisotropy fields per unit stress over twice those developed in FINEMET. Tunable permeability and reduced thicknesses achieved in this process can mitigate eddy-current losses. Giant induced magnetic anisotropies are discussed in light of models for the micromechanisms of amorphous metal deformation, stress-assisted transformations in the crystallites, and directional pair ordering.
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75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
81.40.Gh Other heat and thermomechanical treatments
64.70.K- Solid-solid transitions
75.60.-d Domain effects, magnetization curves, and hysteresis
75.80.+q Magnetomechanical effects, magnetostriction

Magnetic and transport properties of layered LixCo0.5RhO3

Tsuyoshi Takami, Jinguang Cheng, and John B. Goodenough

Appl. Phys. Lett. 101, 102409 (2012); http://dx.doi.org/10.1063/1.4751337 (3 pages)

Online Publication Date: 7 September 2012

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Band insulator Li1.5Co0.5RhO3 has been synthesized, in which Co and Rh atoms are partially disordered in the two-dimensional Co1/3Rh2/3O2 layer. Measurements of magnetic susceptibility indicate that Co(III) and Co(III) are both diamagnetic with low-spin configurations. The electrical resistivity and thermopower reveal one-dimensional variable-range hopping below T1 = 320 K and above T2 = 630 K. Charges introduced by Li extraction down to x = 0.75 in LixCo0.5RhO3 yield the systematic decreases in resistivity and T1, but the magnetic ordering is observed at TN = 30 K, which can be accounted for by spin-orbital coupling with antiferromagnetic interaction.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.20.Ck Nonmetals
72.20.Pa Thermoelectric and thermomagnetic effects
72.20.Ee Mobility edges; hopping transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.50.Ee Antiferromagnetics

The effect of interfaces on magnetic activation volumes in single crystal Co2FeSi Heusler alloy thin films

J. Sagar, H. Sukegawa, L. Lari, V. K. Lazarov, S. Mitani, K. O'Grady, and A. Hirohata

Appl. Phys. Lett. 101, 102410 (2012); http://dx.doi.org/10.1063/1.4749822 (4 pages) | Cited 1 time

Online Publication Date: 7 September 2012

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Structural and magnetization reversal studies have been carried out on single crystal Co2FeSi thin films grown on MgO (001) substrates. The films are highly L21 ordered after annealing above 500 °C. Magnetization reversal has been investigated by measurements of the activation volumes (Vact) within the films. This volume represents the unit of reversal in a magnetic material. Vact (∼4 × 103 nm3) has been found to be independent of the physical structure. Vact is found to correspond to an array of periodic misfit dislocations at the Co2FeSi/MgO interface. Such a small Vact potentially prevents coherent magnetization reversal as required for giant magnetoresistance or tunnel magnetoresistance devices.
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68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments

Positive and negative exchange bias effects in the simple perovskite manganite NdMnO3

Fang Hong, Zhenxiang Cheng, Jianli Wang, Xiaolin Wang, and Shixue Dou

Appl. Phys. Lett. 101, 102411 (2012); http://dx.doi.org/10.1063/1.4751990 (5 pages)

Online Publication Date: 7 September 2012

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Exchange bias effects were studied in the simple perovskite NdMnO3. Nd3+ ordering is induced by the Mn3+ ferromagnetic component, and they are antiferromagnetically coupled with each other. At 30 K, both negative and positive exchange bias effects are found, which are dependent on the cooling field. The exchange bias fields are around −2400 Oe and 1800 Oe, respectively. Positive and negative exchange bias effects were also observed at 8 K, but the exchange bias fields are only 130 Oe and −120 Oe. The coupling intensity between Nd3+ ordering and Mn3+ ordering, and their initial states determine the polarity of the exchange bias fields.
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75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics

Observation of spin-polarized electron transport in Alq3 by using a low work function metal

Hyuk-Jae Jang, Kurt P. Pernstich, David J. Gundlach, Oana D. Jurchescu, and Curt. A. Richter

Appl. Phys. Lett. 101, 102412 (2012); http://dx.doi.org/10.1063/1.4751257 (5 pages)

Online Publication Date: 7 September 2012

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We present the observation of magnetoresistance in Co/Ca/Alq3/Ca/NiFe spin-valve devices. Thin Ca layers contacting 150 nm thick Alq3 enable the injection of spin-polarized electrons into Alq3 due to the engineering of the band alignment. The devices exhibit symmetric current-voltage (I–V) characteristics indicating identical metal contacts on Alq3, and up to 4% of positive magnetoresistance was observed at 4.5 K. In contrast, simultaneously fabricated Co/Alq3/NiFe devices displayed asymmetric I–V curves due to the different metal electrodes, and spin-valve effects were not observed.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
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Phase-controlled superconducting heat-flux quantum modulator

F. Giazotto and M. J. Martínez-Pérez

Appl. Phys. Lett. 101, 102601 (2012); http://dx.doi.org/10.1063/1.4750068 (4 pages) | Cited 5 times

Online Publication Date: 4 September 2012

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We theoretically put forward the concept of a phase-controlled superconducting heat-flux quantum modulator. Its operation relies on phase-dependent heat current predicted to occur in temperature-biased Josephson tunnel junctions. The device behavior is investigated as a function of temperature bias across the junctions, bath temperature, and junctions asymmetry as well. In a realistic Al-based setup the structure could provide temperature modulation amplitudes up to ∼ 50 mK with flux-to-temperature transfer coefficients exceeding ∼ 125 mK/Φ0 below 1 K, and temperature modulation frequency of the order of a few MHz. The proposed structure appears as a promising building-block for the implementation of caloritronic devices operating at cryogenic temperatures.
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85.25.Cp Josephson devices
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors

Alternating current loss of second-generation high-temperature superconducting coils with magnetic and non-magnetic substrate

Min Zhang, J. Kvitkovic, Jae-Ho. Kim, C. H. Kim, S. V. Pamidi, and T. A. Coombs

Appl. Phys. Lett. 101, 102602 (2012); http://dx.doi.org/10.1063/1.4749275 (4 pages) | Cited 1 time

Online Publication Date: 5 September 2012

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It is widely believed that the second-generation high-temperature superconducting (2G HTS) tapes with magnetic substrates suffer higher transport loss compared to those with non-magnetic substrates. To test this, we prepared two identical coils with magnetic and non-magnetic substrates, respectively. The experimental result was rather surprising that they generated roughly the same amount of transport loss. We used finite element method to understand this result. It is found that, unlike in the single tape where the magnetic field-dependent critical current characteristic can be neglected and the effect of magnetic substrate dominates, the magnetic field-dependent critical current characteristic of 2G tape plays as an equally important role as magnetic substrate in terms of HTS coils.
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84.71.Ba Superconducting magnets; magnetic levitation devices
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Conduction mechanisms of epitaxial EuTiO3 thin films

R. Zhao, W. W. Li, L. Chen, Q. Q. Meng, J. Yang, H. Wang, Y. Q. Wang, R. J. Tang, and H. Yang

Appl. Phys. Lett. 101, 102901 (2012); http://dx.doi.org/10.1063/1.4750073 (4 pages) | Cited 1 time

Online Publication Date: 4 September 2012

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To investigate leakage current density versus electric field characteristics, epitaxial EuTiO3 thin films were deposited on (001) SrTiO3 substrates by pulsed laser deposition and were post-annealed in a reducing atmosphere. This investigation found that conduction mechanisms are strongly related to temperature and voltage polarity. It was determined that from 50 to 150 K, the dominant conduction mechanism was a space-charge-limited current under both negative and positive biases. From 200 to 300 K, the conduction mechanism shows Schottky emission and Fowler-Nordheim tunneling behaviors for the negative and positive biases, respectively. This work demonstrates that Eu3+ is one source of leakage current in EuTiO3 thin films.
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75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
68.55.at Other materials
81.15.Fg Pulsed laser ablation deposition
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.80.-e Ferroelectricity and antiferroelectricity

Piezoelectric force microscopy of crystalline oxide-semiconductor heterostructures

M. S. J. Marshall, D. P. Kumah, J. W. Reiner, A. P. Baddorf, C. H. Ahn, and F. J. Walker

Appl. Phys. Lett. 101, 102902 (2012); http://dx.doi.org/10.1063/1.4750243 (4 pages)

Online Publication Date: 5 September 2012

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Thin films of epitaxial SrTiO3 grown on silicon exhibit compressive in-plane strain that may stabilize ferroelectricity in this normally non-ferroelectric material. We investigate this possibility by using an ultra-high vacuum atomic force microscope to measure the local force response of coherently strained SrTiO3 films on silicon to an applied ac electric field. The observed cantilever response is different in regions that were previously written with positive and negative voltages, but the frequency dependence of this response indicates that the dominant forces are related to electrostatic charging rather than ferroelectricity.
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77.55.hn Other piezoelectric or electrostrictive films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.55.ag Semiconductors
77.84.Cg PZT ceramics and other titanates

Prediction of stable ferroelectricity in epitaxial BaTiO3 on Si

H. L. Yu, H. B. Zhang, X. F. Jiang, and G. W. Yang

Appl. Phys. Lett. 101, 102903 (2012); http://dx.doi.org/10.1063/1.4751848 (4 pages)

Online Publication Date: 6 September 2012

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We show theoretically that stable ferroelectricity can be realized in a BaTiO3/Si heterojunction using first-principles calculations. Interfacial ferroelectric behavior is sensitive to the interface structure. Strong ferroelectric-semiconductor interactions would produce a fixed interface polarization and dominate the oxide film polarization properties. Weak interface interaction would be beneficial for preservation of ferroelectricity in the oxide films. The charge transfer between the ferroelectric and the semiconductor, the potential barrier, and the depolarizing field of the ferroelectric also play important roles in heterojunction ferroelectric stability. These findings are useful for silicon-based functional oxide device design.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Cg PZT ceramics and other titanates
77.55.fe BaTiO3-based films
77.22.Ej Polarization and depolarization
68.35.Ct Interface structure and roughness
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
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