Magnetoresistance in cosputtered Cu–Ni–Fe films (abstract)

The magnetoresistance effect, especially the giant magnetoresistance (GMR) effect, has received much attention in recent years. In this study, we discuss the magnetoresistance behavior in Cu–Ni–Fe thin films with Cu content varied from 40 to 90 at.%, prepared by the cosputtering of both Cu and Fe50Ni50 targets. Films with low Cu content, for example, Cu50Ni25Fe25 and Cu40Ni30Fe30, exhibit a mixed behavior of GMR and anisotropic magnetoresistance (AMR). The electrical resistivity of these films substantially increases once the field is applied due to the anisotropic magnetoresistance contribution, and then decreases again at higher fields, which is believed to be related to the giant magnetoresistance effect. As a result of a compromise between both the GMR and the AMR effects, the MR ratios of these low Cu content films are only minus 1%–2% both at room temperature and at 4.2 K. However, it is found that the giant magnetoresistance contribution dominates magnetoresistance behavior in films with Cu content higher than 50 at.%. There exists a large drop in resistance at low fields followed by a long tail at high fields in the MR curves for these high Cu content films. The MR ratios of these films show an increasing tendency as temperature decreases, for example, from 3% at room temperature to 11% at 4.2 K for Cu90Ni5Fe5 film. The GMR effect in these high Cu content films is ascribed to the spin-dependent scattering at the two-phase interface and in the ferromagnetic phase(s), similar to that of the GMR in multilayers, although the contribution from the magnetic fluctuations cannot be excluded.