Eur. Phys. J. B 75, 167-177 (2010)
https://doi.org/10.1140/epjb/e2010-00132-4

Temperature dependence of the electrical resistivity and the anisotropic magnetoresistance (AMR) of electrodeposited Ni-Co alloys

¹ Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, P.O.B. 49, 1525 Budapest, Hungary
² Department of Materials Physics, Eötvös University, P.O.B. 32, 1518 Budapest, Hungary

Corresponding author: tothb@szfki.hu

Received: 1 January 2010
Revised: 17 March 2010
Published online: 6 May 2010

Abstract

The electrical resistivity and the anisotropic magnetoresistance (AMR) was investigated for Ni-Co alloys at and below room temperature. The Ni-Co alloy layers having a thickness of about 2 μm were prepared by electrodeposition on Si wafers with evaporated Cr and Cu underlayers. The alloy composition was varied in the whole concentration range by varying the ratio of Ni-sulfate and Co-sulfate in the electrolyte. The Ni-Co alloy deposits were investigated first in the as-deposited state on the substrates and then, by mechanically stripping them from the substrates, as self-supporting layers both without and after annealing. According to an X-ray diffraction study, a strongly textured face-centered cubic (fcc) structure was formed in the as-deposited state with an average grain size of about 10 nm. Upon annealing, the crystal structure was retained whereas the grain size increased by a factor of 3 to 5, depending on alloy composition. The zero-field resistivity decreased strongly by annealing due to the increased grain size. The annealing hardly changed the AMR below 50 at.% Co but strongly decreased it above this concentration. The composition dependence of the resistivity and the AMR of the annealed Ni-Co alloy deposits was in good quantitative agreement with the available literature data both at 13 K and at room temperature. Both transport parameters were found to exhibit a pronounced maximum in the composition range between 20 and 30 at.% Co and the data of the Ni-Co alloys fitted well to the limiting values of the pure component metals (fcc-Ni and fcc-Co). The only theoretical calculation reported formerly on fcc Ni-Co alloys yielded at T = 0 K a resistivity value smaller by a factor of 5 and an AMR value larger by a factor of about 2 than the corresponding low-temperature experimental data, although the theoretical study properly reproduced the composition dependence of both quantities.