Gesa Beck

The magnetoresistance of homogeneous and heterogeneous silver-rich silver selenide

The magnetoresistance (MR) effect of the low-temperature phase of silver selenide (α-Ag2+δSe) is measured as a function of composition. Very small composition variations in the order of Δδ=10−6 are achieved by coulometric titration and can be performed simultaneously during the MR measurement. A homogeneous Ag2+δSe shows an ordinary magnetoresistance (OMR) effect, which can be well described by the two-band model. For silver selenide with a heterogenous silver excess, we found quite a different MR behavior. Up to a minor silver excess of 1×10−4 10−2) shows again an OMR effect.

Positive and negative magnetoresistance in the system silver-selenium

The (transversal) magnetoresistance (MR) effect of bulk Ag 2+δ Se (δ = 0; 5 x 10 -4 ; 0.33) in its low-temperature α-phase has been measured at temperatures -100°C < T < 50°C in magnetic fields up to B = 8 T. A stoichiometric sample with well-controlled metal excess was prepared by growth from the elements and subsequent electrochemical treatment. The MR effect of this sample is relatively small and positive. Silver-rich material exposes both relatively large positive and negative effects, depending on the metal content.

Effect of current density on composition and structure of electrodeposited Au–Ni alloy coatings

Abstract The effect of current density on composition and structure of galvanic Au–Ni alloy coatings electrodeposited from weakly acidic additive free electrolyte was investigated. At low current density (up to ∼10 mA cm−2), light yellow coloured alloys enriched with Au are deposited. At higher current density the Ni content is abruptly increased and the coatings become coarse and dark. Deposits with an average content of Ni up to ∼50 at-% were obtained. Only a small amount of Ni (up to 20 at-%) takes part in the formation of non-equilibrium super saturated Au–Ni solid solution. The remainder of the Ni is deposited in the interglobular space as an amorphous Ni oxide–hydroxide or as Ni bearing hydroxide salts. Besides Ni, the alloy coatings contain C, N, O, K and H.