Direct current plating, pulse plating, two-pulse plating, and reverse pulse plating were used to produce electrodeposited Co-Cu alloys and Co-Cu/Cu multilayers under galvanostatic control from an electrolyte containing CoSO 4 and CuSO 4 . Atomic force microscopy, X-ray diffraction, and transmission electron microscopy were used to study the sample structure and morphology. Direct current plating resulted in a Co 95 Cu 5 alloy with nearly equal amounts of face-centered cubic ͑fcc͒ and hexagonal close packed phases, while all pulsed current methods yielded multilayers with fcc structure. Giant magnetoresistance ͑GMR͒ behavior was observed in the multilayers with a maximum magnetoresistance ͑MR͒ ratio of about 9% as measured at 8 kOe. The shape of the MR curves and the magnitude of the GMR were very similar, regardless of the sign of the current between the Co deposition pulses. The results of structural studies also confirmed the formation of a multilayer structure for each pulsed electrodeposition mode. The conclusion was that the spontaneous exchange reaction between Co and Cu 2ϩ is responsible for the formation of a pure Cu layer even under reverse pulse plating conditions. The GMR of the multilayer deposits decreased with increasing bilayer number, due to the deterioration of the microstructure as the deposit grew.
We have measured the plasmon dispersion of diamond along the high-symmetry directions using electron energy-loss spectroscopy in transmission. We found the plasmon dispersion to be considerably anisotropic. A comparison of the experimental results to ab initio calculations that take local-field effects into account demonstrates the importance of local-field effects for the dielectric response of systems with strongly inhomogeneous electron distributions.
It turned out from room temperature electrical resistivity and magnetoresistance studies of electrodeposited Co metal and Co(Ru) dilute alloys that the incorporation of a small amount of Ru into Co significantly reduces the anisotropic magnetoresistance (AMR). The influence of Ru on the AMR of Co is explained by a drastic change of the asymmetry of d-band spin-up and spin-down electronic states at the Fermi level as revealed also by recent electronic band-structure calculations on Co-rich Co-Ru alloys.Introduction. -Extensive magnetoresistance (MR) studies have already been performed for magnetic/non-magnetic Co/Ru multilayers [1-4] and sandwiches [3,[5][6][7]. Although a clear giant magnetoresistance (GMR) effect has been observed in each case, its magnitude remained rather small (typically 0.1% at room temperature). This is in contrast to theoretical predictions made on the basis of the resistivity change caused by Ru impurities in a Co matrix [8]. It has been indicated in a recent study [5] that for Co/Ru multilayers and sandwiches, either sputtered or evaporated, a strong chemical intermixing occurs at the Co/Ru interface. It was argued that this intermixing, promoted by the complete mutual solubility of Co and Ru in the hexagonal close-packed (hcp) structure [9], leads to a strong reduction of both the GMR and the interlayer exchange coupling. In fact, the latter was found to be more than an order of magnitude smaller [5] than the theoretical prediction [10]. In view of the fact that a fairly large GMR is expected for the Co-Ru system, on the basis of the large spin asymmetry at the Fermi level [8], the observed GMR is, indeed, also very small.However, whereas the interlayer exchange coupling can certainly be very effectively reduced by interfacial intermixing [11][12][13], a weak antiferromagnetic coupling or the lack of coupling does not necessarily results in very small GMR [14]. For example, it has been demonstrated
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