In the present work, a detailed field dependence of the resistivity of Ni75Co25 and
Ni40Co60 bulk alloys was measured at T = 3 K and 300 K up to high magnetic fields.
The focus of the study was to determine the anisotropic magnetoresistance (AMR) and
to get a quantitative description of the field-induced resistivity change, the latter
not yet being available for Ni-Co alloys. The AMR parameters were derived from the
resistivity data in the magnetically saturated (monodomain) state by using the Kohler
analysis. The values of the AMR ratio were found to be close to the relevant previous
data both at low and high temperatures. Due to the measurement precision and careful
data evaluation, our AMR data obtained on well-characterized samples can be considered
as reference values for the bulk state of the investigated compositions. In addition,
also the resistivity anisotropy splitting was determined. The experimentally found
field dependence of the resistivity at both T = 3 K and 300 K was found to be at variance
with the current theoretical descriptions both for the resistivity increase due to
the ordinary magnetoresistance effect being significant at T = 3 K and for the resistivity
decrease due to the magnon suppression process at T = 300 K, invoking for a refinement
of theory in both cases.
