Magnetoresistance in granular films formed by CoFe and phase change material

Magnetoresistance having a field and current dependence like that of GMR (but a rather small magnitude) has been observed in Co₇₀Fe₃₀/GeTe and Co₇₀Fe₃₀/Ge₂Sb₂Te₅ granular films. Film stacks were fabricated using tandem (multilayer) deposition and annealing was required for the films to develop the GMR-type response. This GMR-type behavior is distinct from AMR, which is observed before annealing. With films having the structure [CoFe 4 nm/GeTe 6 nm]₁₀, a magnetoresistance (MR) of 0.19 %, which has the GMR-type character can be observed after an optimal annealing temperature of 450 °C. TEM and X-ray reflectometry suggest that columnar granules with layered Fe form during deposition and with annealing. Magnetoresistive transport is believed to be between the discontinuous layers in each columnar grain. These discontinuous layers are observed to be superparamagnetic in SQUID ZFC-FC measurements measured from 5–300 K. Magnetoresistance can be fitted by the quadratic relation appropriate for GMR in granular films, especially at higher GeTe compositions. When Ge₂Sb₂Te₅ is used instead of GeTe, higher anneal temperatures are required before the MR with GMR character appears. This GMR type response does not appear when pure Fe is used instead of the CoFe alloy, with the samples showing only AMR in this case. This is due to the absence of Co which seems to cause a more granular growth.     

Pyroelectric effect induced by the built-in field of the p-n junction in the quantum paraelectric PbTe: experimental study

We report here the first observation of a pyroelectric effect in a nonpolar semiconductor. This effect originates in the temperature-dependent electric dipole of the PbTe p-n junction. The junction was illuminated by a chopped CO(2) laser beam, and periodic and single-pulse pyroelectric signals were observed and measured as a function of temperature, reverse bias voltage, and chopper frequency. The measured pyroelectric coefficient is approximately 10(-3) microC/cm(2) K in the region of 40-80 K. The theoretical model describes quantitatively all experimental features. The time evolution of the temperature inside the junction region was reconstructed.     

The power of thought experiments

According to popular opinion, thought experiments are limited in scope, since no novel empirical results could be expected to be produced by thought alone. Yet consider the spectacular 16th century experiment by Stevin. leading to the discovery of the principles of the resolution and combination of forces. He conducted no experiments, for he derived his novel and highly important conclusions by several steps of ingenious reasoning alone. To understand why mental experiments may serve as very effective scientific tools. we need to explicate carefully their underlying mechanism. Thought experiments invariably involve the widely debated notion of counterfactual conditionals. A variety of historical examples are offered designed to illustrate the nature of thought experiments, their associated counterfactual conditionals. as well a the nature of the vital link between the two.     

ISFETs with sputtered sodium alumino-silicate glass membranes

Sodium ion sensitive field-effect transistors (ISFETs) based on reactively sputtered sodium aluminosilicate (NAS) glass membranes are investigated. Using an inverted cylindrical magnetron, NAS films with defined and reproducible composition are obtained. Radiation damage in the gate dielectric is largely eliminated by annealing at 450°C. The Na⁺ sensitivity, the selectivity with respect to H⁺ and K⁺ ions, the response time, the conditioning period, the long-term drift, and the lifetime are evaluated. The ISFETs exhibit a near-Nernstian Na⁺ response down to 10^-4 mol/l in solutions of pH7. The NAS films are physically very robust and have excellent chemical durability, e.g., a sensor with a 110 nm thick membrane lasts for about 8 months. The overall sensor properties compare well with those of a commercial Na⁺ selective glass electrode.     

Synthetic ion channel activity documented by electrophysiological methods in living cells

Hydraphiles are synthetic ion channels that use crown ethers as entry portals and that span phospholipid bilayer membranes. Proton and sodium cation transport by these compounds has been demonstrated in liposomes and planar bilayers. In the present work, whole cell patch clamp experiments show that hydraphiles integrate into the membranes of human embryonic kidney (HEK 293) cells and significantly increase membrane conductance. The altered membrane permeability is reversible, and the cells under study remain vital during the experiment. Control compounds that are too short (C(8)-benzyl channel) to span the bilayer or are inactive owing to a deficiency in the central relay do not induce similar conductance increases. Control experiments confirm that the inactive channel analogues do not show nonspecific effects such as activation of native channels. These studies show that the combination of structural features that have been designed into the hydraphiles afford true, albeit simple, channel function in live cells.     

ISFETs with sputtered sodium alumino-silicate glass membranes

Sodium ion sensitive field-effect transistors (ISFETs) based on reactively sputtered sodium aluminosilicate (NAS) glass membranes are investigated. Using an inverted cylindrical magnetron, NAS films with defined and reproducible composition are obtained. Radiation damage in the gate dielectric is largely eliminated by annealing at 450 degrees C. The Na(+) sensitivity, the selectivity with respect to H(+) and K(+) ions, the response time, the conditioning period, the long-term drift, and the lifetime are evaluated. The ISFETs exhibit a near-Nernstian Na(+) response down to 10(-4) mol/l in solutions of pH>/=7. The NAS films are physically very robust and have excellent chemical durability, e.g., a sensor with a 110 nm thick membrane lasts for about 8 months. The overall sensor properties compare well with those of a commercial Na(+) selective glass electrode.     

A Suggestion for an Integrability Notion for Two-Dimensional Spin Systems

We suggest that trialgebraic symmetries might be a sensible starting point for a notion of integrability for two dimensional spin systems. For a simple trialgebraic symmetry we give an explicit condition in terms of matrices which a Hamiltonian realizing such a symmetry has to satisfy and give an example of such a Hamiltonian which realizes a trialgebra recently given by the authors in another paper. Besides this, we also show that the same trialgebra can be realized on a kind of Fock space of q-oscillators, i.e. the suggested integrability concept gets via this symmetry a close connection to a kind of noncommutative quantum field theory, paralleling the relation between the integrability of spin chains and two dimensional conformal field theory.     

Parallelverschiebung und Krümmungstensor

Ohne ZusammenfassungGießen, Mathem. Seminar, den 17. April 1927.