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Abstract: In this work, the magnetic and microstructural properties of CoPt nanowires are presented as a function of the electrolyte pH and current density during electrodeposition into anodized alumina templates. CoPt nanowires of high aspect ratio have been prepared using electrolyte pH values in the range from 2 to 6. The as-made samples exhibit a face centered cubic (fcc) structure with soft magnetic properties which transform into the face centered tetragonal (fct) L10 phase after thermal treatment. Different pH values of the electrolyte during electrodeposition lead to significantly different microstructures and, therefore, different magnetic properties. The CoPt nanowires prepared at high pH value are composed of fcc nanorods of about 25nm in length. Thermal annealing of these samples leads to a preferred (001) orientation (along the direction perpendicular to the direction of nanowires) which increases with annealing time. On the other hand, the CoPt nanowires prepared at lower pH value are composed of uniform fcc nanograins with the size ∼2−3nm. Magnetization curves for the later sample are virtually identical in both directions indicating an isotropic behavior. [Copyright &y& Elsevier]

Abstract: FePt nanoparticles with perpendicular magnetic anisotropy embedded in non-magnetic matrices M (M=Ag, C) have been fabricated by sputtering FePt/M multilayer films onto single crystal MgO [001] at temperatures above 300°C. Particles with controlled particle size down to a few nanometers and tailored microstructure and magnetic properties can be obtained by varying the bilayer thicknesses, the substrate temperature, the type of substrate material and the post-annealing conditions. Ordered FePt nanoparticles have also been prepared directly by gas phase condensation techniques (cluster gun).The cluster gun allows a better control of particle size and distribution, and enables an in situ heat treatment of the particles to transform their structure into the desired phase before they are deposited onto the substrate, thus avoiding the undesirable effects of alloying and oxidation. [Copyright &y& Elsevier]

Ultrafine Gd particles in a Cu metallic matrix have been obtained by post-annealing of as-sputtered metastable Gd/sub x/Cu/sub 1-x/ alloys at temperatures higher than 250/spl deg/C. The results of resistivity measurements show that the resistivities of as-sputtered metastable Gd/sub 0.2/Cu/sub 0.8/ and Gd/sub 0.3/Cu/sub 0.7/ alloys exhibit a resistivity minimum at low temperatures, an indication of the Kondo effect. In addition the temperature of the resistivity minimum rises with the increasing Gd content. Conversely, the resistivity of films after formation of Gd granules levels off at low temperatures. The magnetic results indicate that the metastable GdCu alloys are essentially a spin-glass at low temperature with the transition temperatures at around 3.5/spl sim/5 K. However, magnetization data at 80 K shows that the as-sputtered samples contain some small Gd ferromagnetic clusters in the paramagnetic matrix. The magnetic particles of granular films begin to be thermally blocked at T/sub B/ and become magnetically ordered below T/sub B/. Due to larger grain sizes, T/sub B/ is much higher for x=0.3 than for 0.2. The variation of transport and magnetic properties for samples with different annealing processes are described in detail. [ABSTRACT FROM PUBLISHER]

Abstract: Prototype metallic magnetic calorimeters (MMC), in which the magnetization of Au:Er sensors has been measured using a DC SQUID, have shown excellent energy resolution for soft X-rays. However, the results to date have been obtained with devices assembled by hand, placing a small ( diameter), thin disk of the Au:Er alloy within the loop of the SQUID. This is an unacceptable method for fabricating large focal-plane arrays of detectors required for the next generation of X-ray telescopes. We are therefore investigating the properties of vapor-deposited films produced by DC magnetron sputtering using an Au:Er alloy target. The magnetic properties of thick Au:Er films have been investigated from room temperature down to 40mK. The measured magnetization matches theoretical values down to 200mK. The films have the same Er concentration as in the target material. At lower temperatures there is indication of enhanced magnetic interactions among the Er ions. We are studying the dependence of this interaction on the parameters used in the deposition process. [Copyright &y& Elsevier]