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24 Jan 2000

Volume 76, Issue 4, pp. 397-519

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Direct observation of subpicosecond single-flux-quantum generation in pulse-driven Y–Ba–Cu–O Josephson junctions

Roman Adam, Marc Currie, Carlo Williams, Roman Sobolewski, Oliver Harnack, and Marian Darula

Appl. Phys. Lett. 76, 469 (2000); http://dx.doi.org/10.1063/1.125790 (3 pages) | Cited 6 times

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We report our time-resolved measurements of switching dynamics of grain-boundary, 5-μm-wide Y–Ba–Cu–O (YBCO) Josephson junctions, excited by 2-ps-wide electrical pulses optically generated by a voltage-biased, 5-μm-wide, 10-μm-long YBCO microbridge. The time-resolved transients were recorded at 20 K using a subpicosecond cryogenic electro-optic sampling system. The intrinsic junction response was separated from the circuit-related feedthrough, and we observed both experimentally and in numerical simulations a 0.8-ps-wide, single-flux-quantum (SFQ) pulse, generated by the switching of the junction with the IcRn product equal to ∼2 mV. At the same time, the measured turn-on delay time was almost three times shorter than that obtained from simulations, questioning applicability of the resistively shunted tunnel junction model to nonhysteretic, high-temperature superconducting weak links. Our test structure's power consumption associated with the single SFQ pulse generation was ∼0.1 μW, leading to a (switching time)×(dissipated power) product equal to 0.08 aJ. © 2000 American Institute of Physics.
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85.25.Cp Josephson devices
85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
84.30.Sk Pulse and digital circuits

Explicit and closed-form expressions for describing magnetic behaviors of uniaxial anisotropy materials

Jeen Hur, Mun Cheol Paek, Kyoung-Ik Cho, and Sung-Chul Shin

Appl. Phys. Lett. 76, 472 (2000); http://dx.doi.org/10.1063/1.125791 (3 pages) | Cited 2 times

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We present explicit, analytic, and closed-form expressions for describing magnetic behaviors of materials having the magnetic anisotropy energy of K sin2 θ. The functional forms of the expressions depend on the ratio of an applied field to an anisotropy field and the ratio of the lowest critical field, for a domain wall to nucleate or move, to the anisotropy field. The present expressions for functions of experimentally measurable quantities gave an elegant method of fitting the quantities to the torque measurement. Furthermore, they may be useful to analyze the ferromagnetic resonance experiment and to measure the distribution of magnetic properties of magnetic aggregates. © 2000 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
02.60.Ed Interpolation; curve fitting
02.30.Ks Delay and functional equations

Appearance of superparamagnetism on heating nanosize Mn0.65Zn0.35Fe2O4

Chandana Rath, N. C. Mishra, S. Anand, R. P. Das, K. K. Sahu, Chandan Upadhyay, and H. C. Verma

Appl. Phys. Lett. 76, 475 (2000); http://dx.doi.org/10.1063/1.125792 (3 pages) | Cited 31 times

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Nanosize particles (average size ∼12 nm) of mixed ferrite Mn0.65Zn0.35Fe2O4 were prepared by the hydrothermal precipitation route and studied using x-ray diffraction, transmission electron microscopy, differential scanning calorimetry, magnetization measurements, and Mössbauer spectroscopy. The as-prepared sample was largely ferrimagnetic and, as the sample was annealed at temperatures above 250 °C, it gradually became superparamagnetic. This unexpected behavior is explained by assuming that the cation distribution in the nanosize as-prepared sample is in a metastable state and, as the sample is heated, this distribution changes to a more stable state while the grain size remains nearly the same. © 2000 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Gg Ferrimagnetics
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.40.Gh Other heat and thermomechanical treatments
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Exchange-biased La2/3Ca1/3(Sr1/3)MnO3 ultrathin films

K. R. Nikolaev, I. N. Krivorotov, W. K. Cooley, A. Bhattacharya, E. Dan Dahlberg, and A. M. Goldman

Appl. Phys. Lett. 76, 478 (2000); http://dx.doi.org/10.1063/1.125793 (3 pages) | Cited 15 times

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Exchange-induced unidirectional anisotropy in trilayers consisting of a thin conductive ferromagnetic layer of La2/3Ca1/3(Sr1/3)MnO3 sandwiched between two antiferromagnetic layers of La1/3Ca2/3MnO3 has been demonstrated through studies of magnetization, magnetoresistance, and in-plane anisotropy of magnetoresistance. The structures were grown by ozone-assisted molecular beam epitaxy and were characterized by a number of techniques. The possibility for the development of exchange-biased magnetic tunnel junctions using these nonclassic double-exchange ferromagnets is discussed. © 2000 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.47.Gk Colossal magnetoresistance
75.30.Gw Magnetic anisotropy
75.45.+j Macroscopic quantum phenomena in magnetic systems

Current perpendicular to plane giant magnetoresistance of multilayered nanowires electrodeposited in anodic aluminum oxide membranes

P. R. Evans, G. Yi, and W. Schwarzacher

Appl. Phys. Lett. 76, 481 (2000); http://dx.doi.org/10.1063/1.125794 (3 pages) | Cited 57 times

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Co–Ni–Cu/Cu multilayered nanowires were prepared by electrodeposition using nanoporous aluminum oxide membranes rather than the more usual track-etched polycarbonate membranes as templates. Very large values of the current perpendicular to plane giant magnetoresistance (CPP-GMR) were recorded: 55% at room temperature and 115% at 77 K. The use of aluminum oxide membranes also made possible a study of the effects of annealing on the CPP-GMR. © 2000 American Institute of Physics.
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73.61.At Metal and metallic alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Pq Electrodeposition, electroplating

Local modification of the thin YBa2Cu3O7−y microstrips by the voltage-biased atomic force microscope tip

B. M. Kim, I. S. Song, J. H. Sok, I. H. Song, Y. S. Min, M. K. Kim, and J. W. Lee

Appl. Phys. Lett. 76, 484 (2000); http://dx.doi.org/10.1063/1.125795 (3 pages) | Cited 4 times

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The atomic force microscope (AFM) tip biased at around −15 V is found to be capable of locally modifying the entire thickness of 40-nm-thick semiconducting or superconducting YBa2Cu3O7−y microstrips in air. We show, using combined electrical and AFM measurements, that the local regions underneath the surface of the semiconducting or superconducting YBa2Cu3O7−y microstrips are transformed into either nonconducting or nonsuperconducting regions, respectively, upon applying the negatively biased AFM tip. The conductance of the nonsuperconducting regions is also found to be comparable to that of the superconducting regions before modification at 298 K. © 2000 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
84.40.Az Waveguides, transmission lines, striplines
85.25.-j Superconducting devices

Coupling superconducting-ferromagnetic point contacts by Andreev reflections

Guy Deutscher and Denis Feinberg

Appl. Phys. Lett. 76, 487 (2000); http://dx.doi.org/10.1063/1.125796 (3 pages) | Cited 110 times

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The properties of a device made of two point contacts between normal (N) or ferromagnetic (F) tips, and a superconductor (S), are discussed as a function of the spin polarization and the distance L between the contacts. When L is smaller than the superconductor coherence length ξ, nonlocal Andreev reflections occur: for opposite spin polarizations of the contacts, “mixed” Cooper pairs made of electrons coming one from each tip can be injected into the superconductor. This leads to unusual properties, for instance, the parallel resistance of two S/F contacts goes from infinity for full and equal polarizations, to a finite Andreev value for opposite ones. © 2000 American Institute of Physics.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
74.20.Fg BCS theory and its development
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena

Properties of BaFe12O19 films prepared by laser deposition with in situ heating and post annealing

Y. F. Lu and W. D. Song

Appl. Phys. Lett. 76, 490 (2000); http://dx.doi.org/10.1063/1.125797 (3 pages) | Cited 16 times

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BaFe12O19 films on (001) sapphire substrates are prepared by laser deposition with in situ heating and postannealing. The properties of the films are analyzed by x-ray diffractometry, vibrating sample magnetometer, atomic force microscopy, and Raman spectroscopy. The relationship among the coercivity, crystalline orientation, and grain shape and size is discussed. The film with coercivity of 5.1 kOe has been obtained by laser deposition with postannealing. The film with a preferential c-axis orientation normal to the film plane and the grains having good crystallinity with hexagonal symmetry have been obtained by laser deposition with in situ heating. © 2000 American Institute of Physics.
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75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ss Magnetic recording materials
81.15.Fg Pulsed laser ablation deposition
81.40.Gh Other heat and thermomechanical treatments
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators
68.55.-a Thin film structure and morphology
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