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

TL;DR

This study investigates how temperature affects electrical resistivity and anisotropic magnetoresistance in electrodeposited Ni Co alloys, revealing composition-dependent behaviors and effects of annealing on their microstructure and transport properties.

Contribution

It provides detailed experimental data on resistivity and AMR across compositions and temperatures, including effects of annealing, with good agreement to existing literature and some theoretical insights.

Findings

Resistivity decreases with annealing due to grain growth.

AMR remains stable below 50 at.% Co after annealing.

Both resistivity and AMR show maxima between 20-30 at.% Co.

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 um 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 fit 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=0K 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 results properly reproduced the composition dependence of both quantities.