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5 Sep 2005

Volume 87, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 87, 101107 (2005); http://dx.doi.org/10.1063/1.2039987 (3 pages)

A. David, C. Meier, R. Sharma, F. S. Diana, S. P. DenBaars, E. Hu, S. Nakamura, C. Weisbuch, and H. Benisty
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Tailoring Fe/Ag superparamagnetic composites by multilayer deposition

J. Balogh, D. Kaptás, L. F. Kiss, T. Pusztai, E. Szilágyi, Á. Tunyogi, J. Swerts, S. Vandezande, K. Temst, and C. Van Haesendonck

Appl. Phys. Lett. 87, 102501 (2005); http://dx.doi.org/10.1063/1.2035886 (3 pages) | Cited 7 times

Online Publication Date: 29 August 2005

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Fe/Ag granular multilayers were examined by magnetization and Mössbauer spectroscopy measurements. Very-thin (0.2 nm) discontinuous Fe layers show superparamagnetic properties that can be tailored by the thickness of both the magnetic and the spacer layers. Novel heterostructures, superparamagnetic and ferromagnetic layers stacked in different sequences, were prepared and the specific contribution of the ferromagnetic layers to the low-field magnetic susceptibility was identified.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.20.En Metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Bb Fe and its alloys
76.80.+y Mössbauer effect; other γ-ray spectroscopy

High-quality planar high-Tc Josephson junctions

N. Bergeal, X. Grison, J. Lesueur, G. Faini, M. Aprili, and J. P. Contour

Appl. Phys. Lett. 87, 102502 (2005); http://dx.doi.org/10.1063/1.2037206 (3 pages) | Cited 17 times

Online Publication Date: 29 August 2005

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Reproducible high-Tc Josephson junctions have been made in a rather simple two-step process using ion irradiation. A microbridge (1 to 5 μm wide) is firstly designed by ion irradiating a c-axis-oriented YBa2Cu3O7−δ film through a gold mask such as the nonprotected part becomes insulating. A lower Tc part is then defined within the bridge by irradiating with a much lower fluence through a narrow slit (20 nm) opened in a standard electronic photoresist. These planar junctions, whose settings can be finely tuned, exhibit reproducible and nearly ideal Josephson characteristics. This process can be used to produce complex Josephson circuits.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
61.80.Jh Ion radiation effects

Interaction between superconductor and ferromagnetic domains in iron sheath: Peak effect in MgB2/Fe wires

J. Horvat, W. K. Yeoh, and L. M. Miller

Appl. Phys. Lett. 87, 102503 (2005); http://dx.doi.org/10.1063/1.2039993 (3 pages) | Cited 5 times

Online Publication Date: 30 August 2005

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Interaction between the superconductor and ferromagnet in MgB2/Fe wires results in either a plateau or a peak effect in the field dependence of transport critical current, Ic(H). This is in addition to magnetic shielding of external field. Current theoretical models cannot account for the observed peak effect in Ic(H). This letter shows that the theoretical explanation of the peak effect should be sought in terms of interaction between superconductor and magnetic domain structure, obtained after the remagnetization of the iron sheath by the self-field of the current. There is a minimum value of critical current, below which the remagnetization of the iron sheath and peak effect in Ic(H) are not observed.
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74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
74.25.Sv Critical currents
74.25.F- Transport properties

Suppressing low-frequency noise in La0.8Ba0.2MnO3 films by a simple method of controlling film thickness

H. Touyama, H. Tanaka, T. Kawai, and M. Kanai

Appl. Phys. Lett. 87, 102504 (2005); http://dx.doi.org/10.1063/1.2039996 (3 pages) | Cited 6 times

Online Publication Date: 30 August 2005

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Thin films of La0.8Ba0.2MnO3, whose temperature coefficients of resistance become high at around room temperature, were grown on SrTiO3(100) substrates by conventional pulsed-laser deposition, and the excess low-frequency electrical noise was measured in an ambient magnetic field. The two-probe noise spectra observed at room temperature can be described by the Hooge’s empirical relation. The Hooge parameter normalized by carrier density (γ/n) was strongly dependent on the sample thickness, and films less than 50 nm thick exhibited much lower noise than thicker films. This demonstrated dependence on thickness provides a simple and easy means of suppressing the noise in manganite thin films using conventional techniques.
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72.70.+m Noise processes and phenomena
72.20.-i Conductivity phenomena in semiconductors and insulators
73.61.-r Electrical properties of specific thin films

Room temperature ferromagnetism in laser ablated Ni-doped In2O3 thin films

Nguyen Hoa Hong, Joe Sakai, Ngo Thu Huong, and Virginie Brizé

Appl. Phys. Lett. 87, 102505 (2005); http://dx.doi.org/10.1063/1.2041822 (3 pages) | Cited 53 times

Online Publication Date: 30 August 2005

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Ni-doped In2O3 thin films were fabricated by laser ablation on sapphire and MgO substrates under various conditions. All Ni:In2O3 films are well-crystallized, single phase, and show clear evidences of room temperature ferromagnetism (FM). Ni atoms were well substituted for In atoms, and distributed very uniformly over the whole thickness of the films. However, the films grown at 550 °C have the Ni concentration exactly the same as in the synthesized target, and as the results, they have the best crystallinity and the largest magnetic moment (maximum about 0.7 μB/Ni). The observed FM in this type of wide-band gap semiconductors has proved that by applying appropriate growth conditions, doping few percent of Ni into In2O3 could indeed result in a potential magnetic material.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
81.05.Hd Other semiconductors
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition

Epitaxial Heusler alloy Co2FeSi/GaAs(001) hybrid structures

M. Hashimoto, J. Herfort, H.-P. Schönherr, and K. H. Ploog

Appl. Phys. Lett. 87, 102506 (2005); http://dx.doi.org/10.1063/1.2041836 (3 pages) | Cited 21 times

Online Publication Date: 1 September 2005

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We found that Co2FeSi layers on GaAs(001) grown by molecular-beam epitaxy with high crystal and interface perfection as well as smooth surfaces can be obtained in the low-growth-temperature regime. The layers are thermally robust up to 250 °C. They have long-range order and crystallize in the Heusler-type L21 structure. The easy axis of magnetization is along the [110] direction caused by a dominating uniaxial in-plane magnetic anisotropy component which has an easy axis different from that of the magnetocrystalline anisotropy component.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Is Curie–Weiss law valid in every ferro-to-para transition?

S. Kaur, A. K. Thakur, A. Choudhary, S. S. Bawa, A. M. Biradar, and S. Annapoorni

Appl. Phys. Lett. 87, 102507 (2005); http://dx.doi.org/10.1063/1.2042539 (3 pages) | Cited 10 times

Online Publication Date: 1 September 2005

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The Curie–Weiss law is obeyed where there is a change in the order parameter and the symmetry of molecules at the transition temperature (Tc) of ferro-to-para phase. The ferroelectric transition is not strictly governed by the Curie–Weiss law. In fact, a number of solid ferroelectrics show deviation from the Curie–Weiss law. It has been shown in the present letter that the de-Vries electroclinic liquid crystals, with a wide smectic A (Sm-A) phase and a high electroclinic effect, do not obey the Curie–Weiss law. The nonlayer shrinkage leads to symmetry conservation that makes the observance of soft mode impossible and hence the deviation.
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77.80.B- Phase transitions and Curie point
61.30.Cz Molecular and microscopic models and theories of liquid crystal structure
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals

Antiferromagnetic coupling and perpendicular anisotropy in TbFeCo/NiO multilayers

R. Shan, J. Du, X. X. Zhang, L. Sun, W. W. Lin, H. Sang, T. R. Gao, and S. M. Zhou

Appl. Phys. Lett. 87, 102508 (2005); http://dx.doi.org/10.1063/1.2042639 (3 pages) | Cited 5 times

Online Publication Date: 1 September 2005

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For Tbx(Fe90Co10)100−x(40 nm)/NiO(3.3 nm) multilayers with x = 17 and 19, antiferromagnetic coupling is revealed by both in-plane and out-of-plane hysteresis loops at low temperatures. Magnetic perpendicular anisotropy and out-of-plane coercivity of multilayers are enhanced, in comparison to those of TbFeCo single layer films. The strength of the antiferromagnetic coupling, the perpendicular anisotropy, and out-of-plane coercivity are all reduced at high temperatures. These results can be ascribed to the weakening of antiferromagnetic ordering of NiO spins.
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75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Direct observation of domain-wall pinning at nanoscale constrictions

M. Kläui, H. Ehrke, U. Rüdiger, T. Kasama, R. E. Dunin-Borkowski, D. Backes, L. J. Heyderman, C. A. F. Vaz, J. A. C. Bland, G. Faini, E. Cambril, and W. Wernsdorfer

Appl. Phys. Lett. 87, 102509 (2005); http://dx.doi.org/10.1063/1.2042542 (3 pages) | Cited 56 times

Online Publication Date: 2 September 2005

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In a combined experimental and numerical study, we determine the details of the pinning of domain walls at constrictions in permalloy nanostructures. Using high spatial-resolution (<10 nm) electron holography, we image the spin structure of geometrically confined head-to-head domain walls at constrictions. Low-temperature magnetoresistance measurements are used to systematically ascertain the domain-wall depinning fields in constrictions down to 35 nm width. The depinning fields increase from 60 to 335 Oe with decreasing constriction width and depend on the wall spin structure. The energy barrier to depin the wall from the constriction is quantitatively determined and comparison with the depinning field strength allows us to gauge the energy barrier height of the pinning potential.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
42.40.-i Holography
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.47.Np Metals and alloys
73.63.Bd Nanocrystalline materials
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