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25 May 2009

Volume 94, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 213101 (2009); http://dx.doi.org/10.1063/1.3139865 (3 pages)

Chul-Ho Lee, Jinkyoung Yoo, Young Joon Hong, Jeonghui Cho, Yong-Jin Kim, Seong-Ran Jeon, Jong Hyeob Baek, and Gyu-Chul Yi
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The structural force arising from magnetic interactions in polydisperse ferrofluids

Anrong Wang, Jian Li, and Rongli Gao

Appl. Phys. Lett. 94, 212501 (2009); http://dx.doi.org/10.1063/1.3141487 (3 pages) | Cited 10 times

Online Publication Date: 26 May 2009

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Ionic ZnFe2O4 is a weak magnetic ferrofluid with different particle sizes (a polydisperse ferrofluid), in which the dipolar coupling constant λ is less than 2. By comparing the reduced magnetization curves and initial magnetic susceptibilities of ferrofluids with different particle volume fractions ϕ, it is found that there are field-induced attractive interactions between the colloidal particles, which make them aggregate; this interaction decreases with ϕ. The dipolar coupling constant is so small that particle aggregation cannot be induced by magnetic interaction alone. Thus, it can be concluded from the experimental results that a nonmagnetic attractive interaction is stimulated during the magnetization process for ferrofluids. Using a model based on “large” and “small” particles (the bidisperse model), this nonmagnetic interaction can be explained as a field-induced structural force. This force is enhanced following magnetic interactions between the large particles as the applied magnetic field increases. The field-induced structural force is similar to a depletion force and can also arise in strong magnetic ferrofluids (λ>2) with polydisperse particle sizes under an applied external magnetic field.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Mm Magnetic liquids
82.70.Dd Colloids
75.30.Cr Saturation moments and magnetic susceptibilities
82.70.Kj Emulsions and suspensions

Subnanosecond time response of large-area superconducting stripline detectors for keV molecular ions

A. Casaburi, N. Zen, K. Suzuki, M. Ejrnaes, S. Pagano, R. Cristiano, and M. Ohkubo

Appl. Phys. Lett. 94, 212502 (2009); http://dx.doi.org/10.1063/1.3142419 (3 pages) | Cited 11 times

Online Publication Date: 27 May 2009

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A large-area (200×200 μm2) superconducting stripline detector based on a parallel configuration of superconducting Nb nanowires is presented. We show that the parallel configuration provides a smart way to control the physical nonequilibrium state induced by the molecular impacts, which allows realizing large sensitive area and subnanosecond response at the same time. The experiments were carried out with molecular ions radiation in a keV energy range. The observed rise time was below 400 ps and the relaxation time was 500 ps, the best in this class of superconducting molecular detectors.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
84.40.Az Waveguides, transmission lines, striplines
85.25.-j Superconducting devices

Mechanisms for higher TC in copper oxide superconductors: Ideas from band calculations

T. Jarlborg

Appl. Phys. Lett. 94, 212503 (2009); http://dx.doi.org/10.1063/1.3142877 (3 pages) | Cited 3 times

Online Publication Date: 27 May 2009

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Band calculations for the hole-doped La2CuO4 system show that artificial periodicities of Ba dopants can give the material different properties than from a uniform distribution of dopants. A periodicity within the planes make static pseudogaps, which could be tuned to raise the density-of-states at EF and the superconducting TC. A periodic doping dependence perpendicular to the CuO planes can increase the matrix element for spin fluctuations.
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74.25.Jb Electronic structure (photoemission, etc.)
61.72.up Other materials
74.62.Dh Effects of crystal defects, doping and substitution
74.72.-h Cuprate superconductors
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.40.-n Fluctuation phenomena

Electric field manipulation of magnetization at room temperature in multiferroic CoFe2O4/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructures

J. J. Yang, Y. G. Zhao, H. F. Tian, L. B. Luo, H. Y. Zhang, Y. J. He, and H. S. Luo

Appl. Phys. Lett. 94, 212504 (2009); http://dx.doi.org/10.1063/1.3143622 (3 pages) | Cited 26 times

Online Publication Date: 27 May 2009

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Multiferroic heterostructures were fabricated by growing ferrimagnetic CoFe2O4 films on ferroelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates using pulsed laser deposition. Upon applying an electric field, the in-plane magnetization of the heterostructures increases and the out-of-plane magnetization decreases. Sharp and reversible changes in magnetization under electric field were also observed for the poled sample. The relative change in magnetization-electric field hysteresis loops were obtained for both the in-plane and out-of-plane magnetizations. Analysis of the results suggests that the electric field induced change in magnetic anisotropy via strain plays an important role in the magnetoelectric coupling in the heterostructures.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.50.Gg Ferrimagnetics
81.15.Fg Pulsed laser ablation deposition

Spin-transfer-torque-induced ferromagnetic resonance for Fe/Cr/Fe layers with an antiferromagnetic coupling field

Takeshi Seki, Hiroyuki Tomita, Ashwin A. Tulapurkar, Masashi Shiraishi, Teruya Shinjo, and Yoshishige Suzuki

Appl. Phys. Lett. 94, 212505 (2009); http://dx.doi.org/10.1063/1.3143625 (3 pages) | Cited 3 times

Online Publication Date: 27 May 2009

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In order to understand the effect of spin-transfer-torque (STT) on artificial magnetic structures, STT-induced and magnetic field-induced ferromagnetic resonances (FMRs) were investigated for Fe/Cr/Fe layers with an antiferromagnetic coupling field. The magnetic field-induced FMR showed high resonant frequency at zero magnetic field owing to the antiferromagnetic coupling field. FMR modes characteristic of antiferromagnetic coupling were induced by STT. From the STT-FMR spectra, the critical current density for magnetization instability was estimated to be ∼ 7×107 A/cm2, suggesting the possibility that STT gives rise to the dynamic phase of magnetization in such artificial magnetic structures.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Room-temperature ferromagnetism in dielectric GaN(Gd)

V. I. Litvinov and V. K. Dugaev

Appl. Phys. Lett. 94, 212506 (2009); http://dx.doi.org/10.1063/1.3143670 (3 pages) | Cited 8 times

Online Publication Date: 27 May 2009

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We present an explanation of recently observed giant magnetic moment and room-temperature ferromagnetism in the dielectric GaN doped with Gd. Our approach uses the polarization mechanism of exchange interaction, which occurs if the d-level of Gd appears in the bandgap close to the valence band edge. Calculated ferromagnetic critical temperature and the value of the magnetic moment well correspond to experimental findings.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions
71.20.-b Electron density of states and band structure of crystalline solids
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Reproducible manipulation of spin ordering in ZnCoO nanocrystals by hydrogen mediation

Seunghun Lee, Yong Chan Cho, Sung-Jin Kim, Chae Ryong Cho, Se-Young Jeong, Su Jae Kim, Jong Pil Kim, Yong Nam Choi, and Jean Man Sur

Appl. Phys. Lett. 94, 212507 (2009); http://dx.doi.org/10.1063/1.3136845 (3 pages) | Cited 17 times

Online Publication Date: 28 May 2009

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Through a simple post hydrogen plasma treatment, we show the strong inducement of the room temperature ferromagnetism in Zn0.9Co0.1O:H nanocrystals fabricated by sol-gel process. X-ray diffraction, high resolution transmission electron microscopy, and neutron high resolution powder diffraction measurements of Zn0.9Co0.1O nanocrystals before and after hydrogenation process confirmed that there are no structural changes in nanocrystal and any creation of magnetic secondary phase. Nevertheless, the clear ferromagnetic hysteresis loop of the hydrogenated Zn0.9Co0.1O nanocrystal was observed in superconducting quantum interference device. These results indicate that the ferromagnetism can be derived from a short-range spin ordering by hydrogen mediation in Co doped ZnO.
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81.07.Bc Nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
52.77.-j Plasma applications
75.50.Pp Magnetic semiconductors

Direct measurement of thin-film thermoelectric figure of merit

Rajeev Singh, Zhixi Bian, Ali Shakouri, Gehong Zeng, Je-Hyeong Bahk, John E. Bowers, Joshua M. O. Zide, and Arthur C. Gossard

Appl. Phys. Lett. 94, 212508 (2009); http://dx.doi.org/10.1063/1.3094880 (3 pages) | Cited 8 times

Online Publication Date: 28 May 2009

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We utilize the transient Harman technique to measure the thermoelectric figure of merit of thin films. A device structure is designed and fabricated to extract the thermoelectric properties of 20 μm thick film composed of InGaAlAs semiconductor with embedded ErAs nanoparticles. High-speed voltage measurements with 63 dB of dynamic range and 200 ns resolution are achieved. Surface temperature measurements of the devices are used to extract the cross-plane Seebeck coefficient and thermal conductivity of the thermoelectric material. Self-consistent finite-element simulations of the three-dimensional temperature distributions in the active devices are in close agreement with the experimental thermal maps.
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85.80.Fi Thermoelectric devices
68.55.ag Semiconductors
73.61.Ey III-V semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
66.70.Df Metals, alloys, and semiconductors

Optical band gap and magnetic properties of unstrained EuTiO3 films

J. H. Lee, X. Ke, N. J. Podraza, L. Fitting Kourkoutis, T. Heeg, M. Roeckerath, J. W. Freeland, C. J. Fennie, J. Schubert, D. A. Muller, P. Schiffer, and D. G. Schlom

Appl. Phys. Lett. 94, 212509 (2009); http://dx.doi.org/10.1063/1.3133351 (3 pages) | Cited 10 times

Online Publication Date: 28 May 2009

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Phase-pure, stoichiometric, unstrained, epitaxial (001)-oriented EuTiO3 thin films have been grown on (001) SrTiO3 substrates by reactive molecular-beam epitaxy. Magnetization measurements show antiferromagnetic behavior with TN = 5.5 K, similar to bulk EuTiO3. Spectroscopic ellipsometry measurements reveal that EuTiO3 films have a direct optical band gap of 0.93±0.07 eV.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Magnetic and transport properties of n-type Fe-doped In2O3 ferromagnetic thin films

Xiao-Hong Xu, Feng-Xian Jiang, Jun Zhang, Xiao-Chen Fan, Hai-Shun Wu, and G. A. Gehring

Appl. Phys. Lett. 94, 212510 (2009); http://dx.doi.org/10.1063/1.3147190 (3 pages) | Cited 12 times

Online Publication Date: 29 May 2009

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Room temperature ferromagnetism was observed in n-type Fe-doped In2O3 thin films deposited on c-cut sapphire substrates by pulsed laser deposition. Structure, magnetism, composition, and transport studies indicated that Fe occupied the In sites of the In2O3 lattice rather than formed any metallic Fe or other magnetic impurity phases. Magnetic moments of films were proved to be intrinsic and showed to have a strong dependence on the carrier densities, which depended on the Fe concentration and its valence state as well as oxygen pressure.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
75.30.Hx Magnetic impurity interactions
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.up Other materials
75.50.Dd Nonmetallic ferromagnetic materials
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