S. Reich

Magnetism induced by the organization of self-assembled monolayers

Unique occurrence of magnetism is shown, in which magnetism appears ex nihilo, when organic molecules are self-assembled as monolayers on gold substrate. The molecules as well as the substrate, when they stand alone, are diamagnetic. Using a superconducting quantum interference device type magnetometer we obtained direct evidence that close-packed organized thio-organic films adsorbed on gold substrates possess magnetic properties at room temperature. The films studied show very high specific magnetization, up to many tens Bohr magnetons per adsorbed molecule, with a very small hysteresis. It is highly anisotropic and shows almost no temperature dependence. The magnetism observed is related to charge transfer between the organic layer and the metal substrate. Yet, the uniqueness here is that many spins are polarized per adsorbed molecules. The magnetic effect is related to the two dimensional organization of the organic molecules on the metal substrate which might explain the high anisotropy.

Magnetic properties of RSr2RuCu2O8+δ (R=Eu and Gd)

Abstract The non superconducting RSr 2 RuCu 2 O 8+ δ (R=Eu and Gd) compounds are magnetically ordered below T N =168 and 185 K, respectively. Magnetic susceptibility (ac and dc) studies indicate that the magnetic ordering is due to the Ru sublattice. The Gd sublattice in GdSr 2 RuCu 2 O 8 is antiferromagnetically ordered at 2.8 K. Irreversibility phenomena and magnetic anomalies, observed at low magnetic fields, originate from antisymmetric exchange coupling of the Dzyaloshinsky–Moria type, and from spin reorientation of the Ru moments. The magnetic behavior of this system and that of the well-known itinerant ferromagnet SrRuO 3 are compared.

Magnetization of small lead particles.

The magnetization of an ensemble of isolated lead grains of sizes ranging from 4 to 1000 nm is measured. A sharp disappearance of the Meissner effect with a lowering of the grain size is observed for the smaller grains. This is a direct observation by magnetization measurement of the occurrence of a critical particle size for superconductivity, which is consistent with Andersons criterion.

Superconducting Hg-1223 films obtained by a sol-gel process

Abstract The preparation of HgBa 2 Ca 2 Cu 3 O 8+δ (Hg-1223) superconducting films is presented. Both the sol-gel process and the superconducting films are novel. The process involves casting a precursor gel of the proper ionic salts in glycerin. The oxidized films obtained after calcination and solid vapor reaction (SVR) with mercury exhibit a superconducting transition at ≈ 135 K and a critical current density of the order of 10 5 A/cm 2 at 10 K. Doping the gel with minute quantites of In 2 O 3 promotes the formation of HgBa 2 Ca 2 Cu 3 phase and is essential for the production of the superconducting films.

Flicker noise of ion-selective membranes and turbulent convection in the depleted layer.

Flicker noise of electric currents through ion-selective membranes is explained. It is attributed to the depletion of salt on one side of the membrane, which creates a thin layer of high resistance. Joule heating in this depletion layer and the ensuing temperature gradient, as well as the concentration gradient, give rise to buoyant forces which may create a turbulent convection current. The turbulence mixes the depletion layer so that the electric resistance fluctuates, and consequently the current flickers.Experiments with ion-selective membranes support this conjecture. They show that 1) Noise is coincident with the increase of the electric resistance by the depletion process. 2) When the current density is reduced, it reaches a critical value, below which the convection current changes from turbulent to laminar, and the noise disappears. 3) Noise reduces with temperature, because the expansion coefficient of water decreases with temperature, and its viscosity increases. 4) A non-ionic water-soluble polymer added to the compartment on the side of the depletion layer reduces the noise, by increasing the bulk viscosity of the solution. 5) Noise depends on the membranes orientation in the gravitational field. 6) The convection-current in the depletion layer can be observed directly, using a laser-beam, by adding latex particles which create optical noise as they drift with the convection current across the beam. The optical noise is observed only coincidently with the current noise.

ANGULAR VARIATION OF COERCIVITY IN ORTHOFERRITE SINGLE CRYSTALS.

The coercive force Hc as a function of the angle between the easy axis of magnetization and the external field has been studied in orthoferrite single crystals using the vibrating sample technique. The experimental results are in good agreement with the Kondorsky 180° wall motion model which predicts the relation Hc(0)/Hc(θ)=cosθ.

Localized High-Tc Superconductivity on the Surface of Na-Doped WO3

WO3 crystals were doped with Na on the surface to ∼7% nominal atomic concentration. Scanning tunneling microscopy and spectroscopy were employed, together with magnetization measurements, in the study of these crystals. Tunneling experiments reveal superconducting islands, 20–150 nm in size, covering about 10% of the surface, the rest of which is insulating. Magnetization measurements show that the superconducting phase formed at the surface has a critical temperature of 91 K, while tunneling spectroscopy yields superconducting gaps having values up to 2Δ/kTc ∼ 4. Presumably most of the sodium is concentrated in these islands and therefore they are metallic in nature, above 30% in atomic concentration. This material is therefore a noncuprate superconductor with a high critical temperature.

Observation of magnetism in Au thin films

Direct magnetization measurements of thin gold films are presented. These measurements integrate the signal from the thin film under study and the magnetic contribution of the film’s interface with the substrate. The diamagnetic contribution to the signal from the bulk substrate is of the same order as the noise level. We find that thin gold films can exhibit positive magnetization. The character of their magnetic behavior is strongly substrate dependent.Direct magnetization measurements of thin gold films are presented. These measurements integrate the signal from the thin film under study and the magnetic contribution of the film’s interface with the substrate. The diamagnetic contribution to the signal from the bulk substrate is of the same order as the noise level. We find that thin gold films can exhibit positive magnetization. The character of their magnetic behavior is strongly substrate dependent.

Measurement of corrosion content of archaeological lead artifacts by their Meissner response in the superconducting state; a new dating method

Meissner fraction in the superconducting state of lead archaeological artifacts is used to evaluate the mass of the uncorroded metal in the sample. Knowing the total mass of the sample, the mass of all corrosion products is established. It is shown that this mass correlates with the archaeological age of the lead artifacts over a time span of ~2500 years. Well-dated untreated lead samples from Tel-Dor, the Persian period, Caesarea, the Byzantine and the Crusader periods as well as contemporary data were used to establish the dating correlation. This new chemical dating method is apparently applicable to lead artifacts buried in soils with 6.5}}

Nonrandom ceramic superconductor‐metal composites

>pH > 6.5. In such soils the corrosion process is very slow and the corrosion products, mainly PbO and PbCO3, accumulate over hundreds of years. The method presented is in principle non-destructive.