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19 Feb 2001

Volume 78, Issue 8, pp. 1023-1163

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Comparison of Josephson vortex flow transistors with different gate line configurations

J. Schuler, S. Weiss, T. Bauch, A. Marx, D. Koelle, and R. Gross

Appl. Phys. Lett. 78, 1095 (2001); http://dx.doi.org/10.1063/1.1346625 (3 pages) | Cited 1 time

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We performed numerical simulations and experiments on Josephson vortex flow transistors based on parallel arrays of YBa2Cu3O7–δ grain boundary junctions with a cross gate line allowing us to operate the same devices in two different modes named the Josephson fluxon transistor (JFT) and Josephson fluxon–antifluxon transistor (JFAT). The simulations yield a general expression for the current gain versus number of junctions and normalized loop inductance and predict higher current gain for the JFAT. The experiments are in good agreement with simulations and show improved coupling between gate line and junctions for the JFAT as compared to the JFT. © 2001 American Institute of Physics.
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85.25.Cp Josephson devices
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.72.-h Cuprate superconductors
02.60.-x Numerical approximation and analysis

Structural and magnetoresistance properties of La2/3Ca1/3MnO3 thin films on buffered silicon substrates

D. Kumar, S. Chattopadhyay, Walter M. Gilmore, C. B. Lee, J. Sankar, A. Kvit, A. K. Sharma, J. Narayan, S. V. Pietambaram, and Rajiv K. Singh

Appl. Phys. Lett. 78, 1098 (2001); http://dx.doi.org/10.1063/1.1350603 (3 pages) | Cited 6 times

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We report an epitaxial growth of LCMO (La2/3Ca1/3MnO3) film on Si by using a highly conducting diffusion barrier layer of TiN. In order to achieve epitaxial growth of LCMO films, MgO, and SrTiO3 films were used as intermediate layers between LCMO and TiN layers. The results have indicated that the properties of LCMO films on Si substrates, deposited under an optimized condition, are on par with the properties of LCMO films on conventional oxide substrates such as LaAlO3 and SrTiO3 in terms of paramagnetic to ferromagnetic transition temperature, insulator to metal transition temperature, and magnetoresistance ratio. © 2001 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
72.60.+g Mixed conductivity and conductivity transitions
81.15.Fg Pulsed laser ablation deposition

Electron spin manipulation using semimagnetic resonant tunneling diodes

Th. Gruber, M. Keim, R. Fiederling, G. Reuscher, W. Ossau, G. Schmidt, L. W. Molenkamp, and A. Waag

Appl. Phys. Lett. 78, 1101 (2001); http://dx.doi.org/10.1063/1.1350600 (3 pages) | Cited 50 times

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One major challenge for the development of spintronic devices is the control of the spin polarization of an electron current. We propose and demonstrate the use of a BeTe/Zn1−xSe/BeTe double barrier resonant tunneling diode for the injection of a spin-polarized electron current into GaAs and the manipulation of the spin orientation of the injected carriers via an external voltage. A spin polarization of up to 80% can be observed with a semimagnetic layer of only 3.5 nm thickness. By changing the resonance condition via the external voltage, the degree of spin polarization can be varied, though a complete spin switching has not yet been accomplished. © 2001 American Institute of Physics.
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85.75.Mm Spin polarized resonant tunnel junctions
75.50.Pp Magnetic semiconductors
85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Low-temperature ordering of L10–CoPt thin films promoted by Sn, Pb, Sb, and Bi additives

O. Kitakami, Y. Shimada, K. Oikawa, H. Daimon, and K. Fukamichi

Appl. Phys. Lett. 78, 1104 (2001); http://dx.doi.org/10.1063/1.1346628 (3 pages) | Cited 76 times

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We have studied the effect of additional elements of Sn, Pb, Sb, and Bi on the ordering of L10–CoPt films. All of these additives are demonstrated to be very effective to promote the ordering and developing of a very large coercivity of the samples annealed at 400 °C. It is worth noting that this annealing temperature for ordering is 200 °C lower than that of pure CoPt. The crystallographic and chemical analyses have revealed that these additives easily diffuse and segregate onto the film surfaces by postannealing because of their very low surface free energy and extremely low solubility in Co. Therefore, it seems reasonable to conclude that the ordering in the CoPt film is significantly promoted at much lower temperature by the aid of a lot of defects produced by the additives excreted by postannealing. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
75.50.Ss Magnetic recording materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
64.75.-g Phase equilibria
68.35.Md Surface thermodynamics, surface energies

Band-gap states and ferroelectric restoration in strontium bismuth tantalate

Biao Li, F. Koch, and L. Chu

Appl. Phys. Lett. 78, 1107 (2001); http://dx.doi.org/10.1063/1.1347011 (3 pages) | Cited 4 times

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By means of photoluminescence (PL) and sub-band-gap (sub-Eg) optical illumination, the degradation and restoration of ferroelectric properties in strontium bismuth tantalate thin films have been investigated, and the existence of band-gap states is demonstrated. It is shown that the suppression and recovery of ferroelectricity are closely correlated with the change of PL intensity, since both switchable polarization and PL are related to Ta5+ ions in the TaO6 octahedron. Furthermore, the electric-field-induced restoration increases dramatically by the aid of sub-band-gap light (2.5 eV ⩽ hν ⩽ Eg) illumination absorbed in band-gap states. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
71.20.Ps Other inorganic compounds
77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization
78.66.Nk Insulators
78.55.Hx Other solid inorganic materials

Low-field magnetoresistance in nanosized La0.7Sr0.3MnO3/Pr0.5Sr0.5MnO3 composites

J.-M. Liu, G. L. Yuan, H. Sang, Z. C. Wu, X. Y. Chen, Z. G. Liu, Y. W. Du, Q. Huang, and C. K. Ong

Appl. Phys. Lett. 78, 1110 (2001); http://dx.doi.org/10.1063/1.1350602 (3 pages) | Cited 41 times

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Nanosized La0.7Sr0.3MnO3/Pr0.5Sr0.5MnO3 (LSMO1−xPSMOx) ceramic composites are prepared using solid-sate sintering. Their microstructural, electro- and magnetotransport properties are characterized by means of various techniques. It is found that the antiferromagnetic/ferromagnetic coupling between PSMO/LSMO at low temperature and the weak ferromagnetic order of PSMO at high temperature results in enhanced low-field magnetoresistance (LFMR) of the composites. With increasing temperature up to 250 K the observed LFMR decays more slowly than that for pure LSMO and this behavior may be explained by the spin coupling near boundaries between LSMO and PSMO grains. © 2001 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.Gk Colossal magnetoresistance
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys
75.30.Et Exchange and superexchange interactions

Evolution of barrier asymmetry in magnetic tunnel junctions

H. Brückl, J. Schmalhorst, G. Reiss, G. Gieres, and J. Wecker

Appl. Phys. Lett. 78, 1113 (2001); http://dx.doi.org/10.1063/1.1350601 (3 pages) | Cited 10 times

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Magnetic tunnel junctions usually consist of different layer stacks at the two sides of the tunneling barrier. The exposure of these junctions to high temperatures thus can induce large asymmetries in the electronic potential with respect to the barrier. Using the example of Co/Cu/Co/Al2O3/Co tunnel junctions, we show that the measured current/voltage characteristics develop a large asymmetry upon annealing at a temperature larger than 230 °C. This is accompanied by a Cu enrichment at one side of the barrier and cannot be explained by simply using the work function differences between the electrode materials. Thus, a Cu–Al2O3 intermixing zone at the barrier interface must be taken into account, which leads to an asymmetric step-like barrier shape. The interpretation is supported by numerical evaluation of model barriers which reproduce the experimental asymmetries if an intermixing zone of only 0.2 nm thickness is assumed. © 2001 American Institute of Physics.
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75.45.+j Macroscopic quantum phenomena in magnetic systems
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.30.+y Surface double layers, Schottky barriers, and work functions
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.50.Ee Antiferromagnetics
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