Room temperature electronic transport properties of Co metal and Co(Ru) dilute alloys

Abstract

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

Anomalous codeposition of cobalt and ruthenium from chloride–sulfate baths

“…There was a small decrease in AMR with the increase in Ru content of the deposits. The AMR achieved in the present work (0.3 %) was of the same order of magnitude than that obtained in an earlier work for Co-Ru alloys with similar compositions [15,16].…”

“…The electrolyte compositions [13][14][15][16] suggested in earlier studies for the electrodeposition of Co-Ru alloys and multilayers were all based on the principle that the salt of the more noble metal has to be used in a low concentration, while that of the less noble metal can be applied in a high concentration, even close to the solubility. A similar electrolyte formulation was described for a FeCoRu bath [7].…”

“…A similar electrolyte formulation was described for a FeCoRu bath [7]. The Ru compound used was either RuCl 3 [7,15,16] or Ru(OH)Cl 3 [13,14] and the electrolyte was very acidic in each case. The polarization behaviour of the Co-Ru system was published only for the bath containing Ru 4+ , Co 2+ , sulfuric acid and sulfamic acid at 60 ºC, and the c(Co 2+ )/c(Ru 4+ ) concentration ratio in the electrolyte was a fixed value of 18.75 [13].…”

Electrochemical deposition of alloys in Ru3+–Co2+–Cl−–H2O system

“…At room temperature a stable Ru phase is hcp. In the solution of Co and Ru the fraction of Co fcc phase decreases in comparison to pure Co [32].…”

Composition, morphology and electrical transport properties of Co–Pb electrodeposits

“…10.a reveals that the AMR value of pure Co ("d.c. plated Co") deposited from the acetate bath void of Pb 2+ is about 0.75 %. On the other hand, a roomtemperature AMR of about 2 % was reported for Co films electrodeposited from a sulfate bath [21] and for evaporated hcp Co films [22]. Since the "d.c. plated Co" sample in the present study was pure Co, the reduced AMR value in comparison with standard values of bulk Co should be ascribed to the fine-grained structure of this deposit.…”