Y. Abulafia

Plastic Vortex Creep in YBa2Cu3O7-x Crystals.

Local magnetic relaxation measurements in YBa2Cu3O72x crystals show evidence for plastic vortex creep associated with the motion of dislocations in the vortex lattice. This creep mechanism governs the vortex dynamics in a wide range of temperatures and fields below the melting line and above the field corresponding to the peak in the “fishtail” magnetization. In this range the activation energy Upl, which decreases with field, drops below the elastic (collective) creep activation energy, Uel, which increases with field. A crossover in flux dynamics from elastic to plastic creep is shown to be the origin of the fishtail in YBa 2Cu3O72x. [S0031-9007(96)00878-2]

Plastic Vortex Creep in YBa{sub {bold 2}}Cu{sub {bold 3}}O{sub {bold 7{minus}}}{ital x} Crystals

Local magnetic relaxation measurements in YBa2Cu3O72x crystals show evidence for plastic vortex creep associated with the motion of dislocations in the vortex lattice. This creep mechanism governs the vortex dynamics in a wide range of temperatures and fields below the melting line and above the field corresponding to the peak in the “fishtail” magnetization. In this range the activation energy Upl, which decreases with field, drops below the elastic (collective) creep activation energy, Uel, which increases with field. A crossover in flux dynamics from elastic to plastic creep is shown to be the origin of the fishtail in YBa 2Cu3O72x. [S0031-9007(96)00878-2]

Diverging time scales for onset of irreversibility in high-temperature superconductors

Abstract The onset temperature, Tirr, for magnetic irreversibility in high-temperature superconductors has been investigated as a function of frequency (0.2 Hz⩽f⩽65 000 Hz) and DC magnetic field (0

Estimation of FMAX and ISB in microprocessors

Inherent process device variations and fluctuations during manufacturing have a large impact on the microprocessor maximum clock frequency and total leakage power. These fluctuations have a statistical distribution that calls for usage of statistical methods for frequency and leakage analysis. This paper presents a simple technique for accurate estimation of product high-level (Full Chip) parameters such as the maximum frequency (FMAX) distribution and the total leakage (ISB). Moreover, this technique can grade critical paths by their failure probability and perform what-if analysis to estimate FMAX after fixing specific speed paths. Using our FMAX/ISB prediction, we show good correlation with silicon measurements from a production microprocessor.

Measurement of the magnetic induction vector in superconductors using a double-layer Hall sensor array

We describe an experimental technique for simultaneous measurement of both the normal (Bz) and the in-plane (Bx) components of the magnetic induction field near the surface of a superconducting sample. This technique utilizes a novel design of a double-layered Hall sensor array fabricated from a GaAs/AlGaAs heterostructure containing two parallel layers of a two-dimensional electron gas. The effectiveness of this technique is demonstrated in measurements of Bx and Bz and the current distribution at the surface of a thin YBa2Cu3O7 crystal.

Investigation of flux creep in high-Tc superconductors using Hall-sensor array

The details of a new method for studying thermally activated flux creep in thin superconducting samples is described. The method employs a linear array of microscopic Hall sensors to measure the time and spatial dependence of the magnetic induction across the sample. These data are analyzed on the basis of the local rate equation for thermally activated flux motion, taking into account both the in-plane and out-of-plane components of the induction field. Following this analysis, flux creep parameters, such as the flux-line current density, flux-line average velocity, and the activation energy for flux creep, can be directly determined as a function of position and time. New experimental data in a superconducting Nd1.85Ce0.15CuO4−δ crystal demonstrate this method.

Hall-array gradiometer for measurement of the magnetic induction vector in superconductors

An experimental technique for measuring the distribution of the normal and planar components of the magnetic induction near the surface of a superconducting sample is described. This technique utilizes a design of a double-layered Hall sensor array fabricated from a GaAs/AlGaAs heterostructure containing two parallel layers of a two-dimensional electron gas. Applications of this technique are demonstrated in measuring the current density distribution and in characterizing the flux creep process in a thin YBa2Cu3O7 crystal.

Comparative study of global and local magnetization measurements on single crystalline high-Tc superconductors

The mixed state of several RE Ba Cu O single crystals REs Y,Yb was investigated by various measuring 23 7 yd

Hall-array measurements of flux creep parameters in Y-Ba-Cu-O crystals

We describe the details of a new method for studying thermally activated flux creep in superconductors. this method employs an array of microscopic Hall sensors to probe the time evolution of the field profile in the sample. We analyze these data on the basis of a continuity equation which takes into account contributions to the relaxation process from both the in-plane and out-of-plane components of the induction field. This analysis enables direct determination of flux creep parameters such as the flux-line current density, flux-line velocity and the activation energy for flux creep. We demonstrate this method by presenting experimental data for YBa2Cu3O7-x crystals in the remanent state and in the presence of a field.

SUSCEPTIBILITY OF ERBA2CU3O6 SINGLE CRYSTAL : A DIPOLAR ANTIFERROMAGNET

The susceptibility of an ErBa2Cu3O6 single crystal was measured at 2 K<T<100 K. The low‐temperature (T<10 K) data yield g∥=5.39 and g⊥=7.45. The shapes of the susceptibility curves are well explained by the dipolar fields, calculated for the Er3+ ions in the layered structure of the sample, and by a small contribution of exchange fields. Extending the calculations to the antiferromagnetic state of ErBa2Cu3O6 shows that this material is well described as a two‐dimensional dipolar antiferromagnet. The dipolar field calculations are also applied to DyBa2Cu3O6 and GdBa2Cu3O6 and are shown to be compatible with the magnetic structure of these materials.