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27 May 2002

Volume 80, Issue 21, pp. 3883-4065

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Observation of coherent oxide precipitates in polycrystalline MgB2

R. F. Klie, J. C. Idrobo, N. D. Browning, A. Serquis, Y. T. Zhu, X. Z. Liao, and F. M. Mueller

Appl. Phys. Lett. 80, 3970 (2002); http://dx.doi.org/10.1063/1.1481239 (3 pages) | Cited 34 times

Online Publication Date: 20 May 2002

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Here we describe the results of an atomic resolution study of oxygen incorporation into bulk MgB2. We find that ∼ 20–100 nm sized precipitates are formed by ordered substitution of oxygen atoms onto boron lattice sites, while the basic bulk MgB2 crystal structure and orientation is preserved. The periodicity of the oxygen ordering is dictated by the oxygen concentration in the precipitates and primarily occurs in the (010) plane. The presence of these precipitates correlates well with an improved critical current density and superconducting transition behavior, implying that they act as pinning centers. © 2002 American Institute of Physics.
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64.75.-g Phase equilibria
74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.62.Dh Effects of crystal defects, doping and substitution
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

High efficiency nonvolatile ferromagnet/superconductor switch

B. Nadgorny and I. I. Mazin

Appl. Phys. Lett. 80, 3973 (2002); http://dx.doi.org/10.1063/1.1481987 (3 pages) | Cited 3 times

Online Publication Date: 20 May 2002

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A composite magnetosuperconducting switch is proposed. The device, which is based on Andreev reflection at the superconductor/ferromagnet contact, combines high efficiency with nonvolatility. The low-impedance state of the device corresponds to the normal state of the superconductor, whereas the high-impedance state corresponds to the superconducting state. The proposed device does not require high-quality Andreev contacts; on the contrary, interface scattering significantly increases the efficiency of the device. Up to 1000%–2500% efficiency can be achieved with the existing ferromagnetic materials. The device can be used as a basic element for nonvolatile logic and memory. © 2002 American Institute of Physics.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.25.Am Superconducting device characterization, design, and modeling
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
84.30.Sk Pulse and digital circuits

Diffusion study of the exchange-biased NiFe/MnIr/CoFe electrode in magnetic tunnel junctions

C. S. Yoon, J. H. Lee, H. D. Jeong, C. K. Kim, J. H. Yuh, and Rick Haasch

Appl. Phys. Lett. 80, 3976 (2002); http://dx.doi.org/10.1063/1.1481185 (3 pages) | Cited 16 times

Online Publication Date: 20 May 2002

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The exchange-biased electrode of magnetic tunneling junctions with under- and overoxidized AlOx insulator layers were annealed at 300 °C to study the extent of the Mn diffusion. A significant amount of Mn diffusion into the AlOx layer was observed in the overoxidized junction sample from Auger electron spectroscopy and the extent of Mn diffusion increased with increasing oxidation time. X-ray photoelectron spectroscopy (XPS) proved that Mn found at the CoFe/AlOx interface in the overoxidized junction sample was in the form of Mn oxide. The XPS data suggest that the Mn diffusion was accelerated by the preferential oxidation of Mn at the CoFe/AlOx interface. © 2002 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.65.Ac Multilayers
81.40.Gh Other heat and thermomechanical treatments
85.75.Mm Spin polarized resonant tunnel junctions
81.65.Mq Oxidation
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Scanning tunneling potentiometry search for mesoscopic phase separation in La0.7Sr0.3MnO3

B. Grévin, I. Maggio-Aprile, A. Bentzen, O. Kuffer, I. Joumard, and Ø. Fischer

Appl. Phys. Lett. 80, 3979 (2002); http://dx.doi.org/10.1063/1.1481787 (3 pages) | Cited 7 times

Online Publication Date: 20 May 2002

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Optimally doped epitaxial La0.7Sr0.3MnO3/SrTiO3 thin films have been probed by scanning tunneling potentiometry in a search for possible mesoscopic phase separation. The experiments were performed in ultrahigh vacuum after an in situ deposition, which prevents local inhomogeneities from forming due to surface contamination. Resulting reproducible two-dimensional images reveal clear topographic features and continuous potentiometric variations. These results support the idea that mesoscopic phase separation is not a generic feature shared by all optimally doped manganites. © 2002 American Institute of Physics.
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68.55.Nq Composition and phase identification
64.75.-g Phase equilibria
68.35.Dv Composition, segregation; defects and impurities
73.61.-r Electrical properties of specific thin films

Efficient characterization of ultrathin AlOx insulating barriers in magnetic tunnel junctions fabricated by masked rf plasma oxidation technique

J. H. Park, G. S. Lee, J. Y. Yang, K. S. Yoon, C. O. Kim, J. P. Hong, and H. J. Kim

Appl. Phys. Lett. 80, 3982 (2002); http://dx.doi.org/10.1063/1.1481538 (3 pages) | Cited 6 times

Online Publication Date: 20 May 2002

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AlOx insulating barriers in magnetic tunnel junctions were prepared by a masked rf plasma oxidation process to reduce direct ion-bombardment effect on the barrier. In our method, the root-mean-square value of 2.1 Å in the barrier and the magnetic resistance ratio up to 32% were observed. In addition, the surface plasmon resonance spectroscopy (SPRS) measurement was performed to efficiently determine optimum oxidation time, dielectric properties, and oxidation states inside thin barrier. The SPRS results revealed that the dielectric value and thickness of the optimum barrier were found to be 1.3576+i1.4488 and 16.3 Å, respectively, with a thickness confirmation by a high resolving transmission electron microscope measurement. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
81.65.Mq Oxidation
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
75.45.+j Macroscopic quantum phenomena in magnetic systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
52.77.-j Plasma applications

All YBa2Cu3O7−δ trilayer junctions with YBa2Cu3O7−δ wiring layers

E. Fujimoto, H. Sato, T. Yamada, and H. Akoh

Appl. Phys. Lett. 80, 3985 (2002); http://dx.doi.org/10.1063/1.1481765 (3 pages) | Cited 6 times

Online Publication Date: 20 May 2002

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We have fabricated all YBa2Cu3O7−δ (YBaCuO) trilayer junctions with YBaCuO wiring layers using CeO2 insulating layers. The trilayer junctions consist of YBaCuO/PrBa2Cu3O7−δ (PrBaCuO)/YBaCuO structures on (100) MgO substrate. Both YBaCuO wiring layer and base-YBaCuO electrode have the critical temperature Tc of ⩾87 K. A 5×5-μm2 junction with a PrBaCuO barrier thickness of 25 nm shows a resistively-shunted-junction (RSJ)-like current–voltage (I–V) characteristic with a critical current density Jc of 1.7×102 A/cm2 and a critical current×normal resistance (IcRn) product of 0.40 mV, and no contact resistance at 4.2 K. The magnetic field dependence of Ic for the junction shows a Fraunhofer interference pattern with a modulation period of 3.5 mT, which is in good agreement with the value estimated from the junction size of 5 μm. In addition, the YBaCuO wiring layers have no structures in the I–V characteristics due to grain–boundary junctions. These facts confirm that the observed Josephson properties come from the YBaCuO/PrBaCuO/YBaCuO trilayer structure. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.25.Sv Critical currents
74.10.+v Occurrence, potential candidates
61.72.Mm Grain and twin boundaries
74.25.F- Transport properties

Extraordinary magnetoresistance effect in a microstructured metal–semiconductor hybrid structure

C. H. Möller, O. Kronenwerth, D. Grundler, W. Hansen, Ch. Heyn, and D. Heitmann

Appl. Phys. Lett. 80, 3988 (2002); http://dx.doi.org/10.1063/1.1481982 (3 pages) | Cited 21 times

Online Publication Date: 20 May 2002

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We have fabricated hybrid structures consisting of a metallic thin film and of a microstructured two-dimensional electron system in an InAs heterostructure. The devices are found to exhibit a huge magnetoresistance (MR) effect in magnetic fields ⩽ 1 T. At low temperature, a value of ΔR/R = [R(B = 1 T)−R(B = 0)]/R(B = 0) as high as 115 000% is measured. The value of ΔR/R has been studied as a function of the electron mobility, the electron density and the lateral width of the semiconductor. We find that the MR effect can be tailored by these different parameters and technological relevant devices can be realized. © 2002 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
81.05.Ea III-V semiconductors
72.20.Ee Mobility edges; hopping transport
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Dn Low-field transport and mobility; piezoresistance
73.20.At Surface states, band structure, electron density of states

Epitaxial PrBa2(Cu0.8Al0.2)3O7 thin films grown by rf sputtering

Mingji Jin, Q. Y. Chen, Udom Tipparach, T. P. Chen, C. Wang, H. W. Seo, Lixi Yuan, W. K. Chu, K. S. No, C. L. Chen, and Y. S. Song

Appl. Phys. Lett. 80, 3991 (2002); http://dx.doi.org/10.1063/1.1481543 (3 pages)

Online Publication Date: 20 May 2002

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Epitaxial thin films of PrBa2(Cu0.8Al0.2)3O7 have been vacuum deposited by rf sputtering on the LaAlO3 substrates. Though electrically much more resistive, these Al-substituted films are all of orthorhombic structure and epitaxial quality on various oxide substrates, much like YBa2Cu3O7 and PrBa2Cu3O7 grown under similar conditions. The samples appeared to be shiny and dark as observed with the naked eye, but their electrical resistivity, ρ(T), ranged from ∼1 Ω cm at room temperature to about six orders of magnitude higher at T ∼ 30 K. From the ρ(T) functional for both the target and the films, which, by and large, follows Mott’s T−1/4 law with their own relevant material constants, we believe that the mechanism of electrical conduction was mainly through variable range hopping. This suggests that the substitution of Al has caused extensive localization of charge carriers. The localization radius is ∼0.2 nm while the hopping distance is ∼3–9 nm. © 2002 American Institute of Physics.
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81.05.Hd Other semiconductors
81.15.Cd Deposition by sputtering
73.61.Le Other inorganic semiconductors
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.50.Dn Low-field transport and mobility; piezoresistance

Artificially induced reduction of the dissipation anisotropy in high-temperature superconductors

E. M. Gonzalez, J. E. Villegas, M. Varela, J. Santamaria, P. Prieto, Ivan K. Schuller, and J. L. Vicent

Appl. Phys. Lett. 80, 3994 (2002); http://dx.doi.org/10.1063/1.1482420 (3 pages) | Cited 2 times

Online Publication Date: 20 May 2002

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Bi2Sr2CaCu2O8, RBa2Cu3O7 (R = Y, Eu) thin films and RBa2Cu3O7/PrBa2Cu3O7 superlattices have been fabricated by sputtering technique. The anisotropic dissipation was measured close to the critical temperatures with high applied magnetic fields rotating from parallel to perpendicular to the substrate. In multilayers, in a large magnetic field interval, the dissipation anisotropy is reduced as much as 60% in comparison with the most anisotropic system (Bi2Sr2CaCu2O8) and at least 50% at 30 kOe in comparison with 123 films. This strong anisotropy reduction is discussed taking into account the role played by the superlattice modulation lengths on magnetic matching effects and coupling between the superconducting layers. © 2002 American Institute of Physics.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.78.Fk Multilayers, superlattices, heterostructures
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.72.-h Cuprate superconductors
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