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8 Mar 2004

Volume 84, Issue 10, pp. 1623-1807

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 1798 (2004); http://dx.doi.org/10.1063/1.1664019 (3 pages)

Bartosz A. Grzybowski, Michal Radkowski, Christopher J. Campbell, Jessamine Ng Lee, and George M. Whitesides
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Tuning negative and positive magnetoresistances by variation of spin-polarized electron transfer into π-conjugated polymers

Feng Luo, Wei Song, Zhe-Ming Wang, and Chun-Hua Yan

Appl. Phys. Lett. 84, 1719 (2004); http://dx.doi.org/10.1063/1.1667264 (3 pages) | Cited 8 times

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A series of polyparaphenyl derivatives with different conductivities have been synthesized to fabricate three kinds of polymer-embedded La0.7Ca0.3MnO3 (LCMO) composites by mixing different weight fractions of polymers and LCMO. X-ray diffraction and Fourier transform infrared spectra show the coexistence of the LCMO particles and polymers and no chemical reactions between each other. By adjusting the conductivity and π electron polarization of polymers, spin-polarized electron transfer from the surfaces of LCMO magnetic particles through the interfacial coupling into polymers can be tuned, leading to the tunable negative and positive magnetoresistances in these composites. This abnormal positive MR can be mainly attributed to the spin-polarized electron tunneling weakening and magnetic scattering enhancement on polarized π electrons through the LCMO/polymer interfaces. © 2004 American Institute of Physics.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
72.80.Tm Composite materials
81.05.Qk Reinforced polymers and polymer-based composites
72.25.Mk Spin transport through interfaces
75.47.Gk Colossal magnetoresistance
78.30.Jw Organic compounds, polymers

Electrostatic modulation of the electronic properties of Nb-doped SrTiO3 superconducting films

K. S. Takahashi, D. Matthey, D. Jaccard, J.-M. Triscone, K. Shibuya, T. Ohnishi, and M. Lippmaa

Appl. Phys. Lett. 84, 1722 (2004); http://dx.doi.org/10.1063/1.1667279 (3 pages) | Cited 16 times

Online Publication Date: 2 March 2004

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We have performed ferroelectric field effect experiments using an epitaxial heterostructure composed of ferroelectric Pb(Zr0.2Ti0.8)O3 and superconducting Nb-doped SrTiO3. The films were prepared on (001) SrTiO3 substrates by off-axis radio-frequency magnetron sputtering and pulsed-laser deposition. By switching the polarization field of the 500-Å-thick Pb(Zr0.2Ti0.8)O3 layer, a large change of about 30% in resistivity and a 20% shift of Tc (ΔTc ∼ 0.05 K) were induced in the 400-Å-thick epitaxial Nb-doped SrTiO3 layer. The relationship between Tc and the electrostatically modulated average carrier concentration can be mapped onto the phase diagram of chemically doped SrTiO3. © 2004 American Institute of Physics.
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74.25.F- Transport properties
74.72.-h Cuprate superconductors
77.80.Fm Switching phenomena
74.78.-w Superconducting films and low-dimensional structures
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
81.15.Fg Pulsed laser ablation deposition
74.25.Dw Superconductivity phase diagrams
61.72.S- Impurities in crystals

Epitaxial growth of the diluted magnetic semiconductors CryGe1−y and CryMnxGe1−x−y

G. Kioseoglou, A. T. Hanbicki, C. H. Li, S. C. Erwin, R. Goswami, and B. T. Jonker

Appl. Phys. Lett. 84, 1725 (2004); http://dx.doi.org/10.1063/1.1668322 (3 pages) | Cited 12 times

Online Publication Date: 2 March 2004

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We report the epitaxial growth of CryGe1−y and CryMnxGe1−x−y(001) thin films on GaAs(001), describe the structural and transport properties, and compare the measured magnetic properties with those predicted by theory. The samples are strongly p type, and hole densities increase with Cr concentration. The CryGe1−y system remains paramagnetic for the growth conditions and low Cr concentrations employed (y ⩽ 0.04), consistent with density functional theory predictions. Addition of Cr into the ferromagnetic semiconductor MnxGe1−x host systematically reduces the Curie temperature and total magnetization. © 2004 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.05.Hd Other semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Dd Nonmetallic ferromagnetic materials

Critical current densities of powder-in-tube MgB2 tapes fabricated with nanometer-size Mg powder

H. Yamada, M. Hirakawa, H. Kumakura, A. Matsumoto, and H. Kitaguchi

Appl. Phys. Lett. 84, 1728 (2004); http://dx.doi.org/10.1063/1.1667263 (3 pages) | Cited 54 times

Online Publication Date: 2 March 2004

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We fabricated powder-in-tube MgB2/Fe tapes using a powder mixture of nanometer-size Mg and commercial amorphous B and investigated the transport properties. High-purity nanometer-size Mg powder was fabricated by applying the thermal plasma method. 5–10 mol % SiC powder doping was tried to enhance the Jc properties. We found that the use of nanometer-size Mg powder was effective to increase the Jc values. The transport Jc values of the nondoped and 10 mol % SiC-doped tapes prepared with nanometer-size Mg powder reached 90 and 250 A/mm2 at 4.2 K and 10 T, respectively. These values were about five times higher than those of the tapes prepared with commercial Mg powder. © 2004 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
81.07.Wx Nanopowders
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
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