Karen Attenborough

Electrodeposited spin valves on n-type GaAs

Soft switching, spin-valve Co/Cu heterostructures have been electrodeposited onto n-type (100) GaAs. A symmetric spin-valve configuration is used which incorporates an artificially hard substructure. A magnetoresistance change of up to 5.4% is observed with sensitivities up to 0.55% per Oersted and a saturation field of 100 Oe, the highest sensitivity so far observed in electrodeposited structures. The magnetoresistance measurements show a double switching step which we conclude is due to the free layers having differing coercivities. The Co/GaAs interface induces an in-plane anisotropy in the films which is responsible for these remarkable spin-valve properties.

Magnetic properties of CoNiFe alloys electrodeposited under potential and current control conditions

Electrodeposited CoNiFe alloys have been produced under potential and current control conditions. It was found that composition, crystalline structure and magnetic properties are the same irrespective of which plating control is used. Magnetic anisotropy is present in the softest samples. A study of the dependence of magnetic properties and domain structure on the thickness of the films is also reported.

Ultra-sensitive spin-valve structures grown on n-GaAs by single bath electrodeposition

Soft switching spin-valve like Co/Cu structures have been electrodeposited onto n-type (100)-GaAs. A symmetric spin-valve configuration is used which incorporates an artificially hard substructure. A magnetoresistance change of up to 6% is observed with high sensitivities ranging up to 0.67% per Oe. The magnetoresistance measurements show characteristics potentially useful for sensing applications, such as a strong angular dependence, together with a double switching step at certain angles.

Correlative transmission electron microscopy and electrical properties study of switchable phase-change random access memory line cells

Phase-change memory line cells, where the active material has a thickness of 15 nm, were prepared for transmission electron microscopy (TEM) observation such that they still could be switched and characterized electrically after the preparation. The result of these observations in comparison with detailed electrical characterization showed (i) normal behavior for relatively long amorphous marks, resulting in a hyperbolic dependence between SET resistance and SET current, indicating a switching mechanism based on initially long and thin nanoscale crystalline filaments which thicken gradually, and (ii) anomalous behavior, which holds for relatively short amorphous marks, where initially directly a massive crystalline filament is formed that consumes most of the width of the amorphous mark only leaving minor residual amorphous regions at its edges. The present results demonstrate that even in (purposely) thick TEM samples, the TEM sample preparation hampers the probability to observe normal behavior and it can be debated whether it is possible to produce electrically switchable TEM specimen in which the memory cells behave the same as in their original bulk embedded state.

Comparison between patterned and unpatterned electrodeposited spin-valve sensors

Electrodeposited spin-valves on GaAs substrates were patterned down into 80 /spl mu/m, 4 /spl mu/m and 2 /spl mu/m strips. A symmetric spin-valve configuration is used which incorporates an artificially hard substructure. Sensitivities up to 1.5%/Oe were observed, these being the highest ever observed in electrodeposited structures. Upon patterning an increased antiferromagnetic contribution of the inner hard substructure was seen.

Enhanced Kerr rotation in electrodeposited nickel films

High quality nickel films were electrodeposited directly onto n-GaAs using galvanostatic control. It was seen that by varying the current density the crystallographic orientation of the films could be controlled. For a current density of 15 mA/cm/sup 2/, a highly dominant (220) crystallographic orientation was obtained. Magnetic measurements revealed a strong uniaxial anisotropy in these films. Moreover, Kerr spectroscopy measurements (1.4 to 4.5 eV) showed an enhanced Kerr rotation of -0.17/spl deg/ at 3.2 eV, which may be attributed to the strong magnetic anisotropy and the exceptional crystal quality of the films.