Effect of addition of Ni on the structure and giant magnetoresistance in Fe-Cu films

Structural and magnetoresistive properties of Fe-Cu-Ni granular thin films exhibiting giant magnetoresistance were investigated. A number of samples were prepared by DC magnetron sputtering at a sputtering pressure of 0.001 mbar of Ar. The compositions of the samples were determined by energy-dispersive X-ray analysis. X-ray diffraction patterns showed only Cu(1 1 1) peaks in all the samples and no Fe or Ni peaks were observed. The behaviour of d1 1 1 of Cu indicates the presence of Ni atoms in the Cu grains. From Vegard's law for bulk Cu-Ni alloy, we have concluded that the value of d1 1 1 of Cu obtained in our samples is a measure of the amount of Ni dissolved in the Cu grains. The electron diffraction patterns obtained on selected samples showed many Cu reflections and they also did not show any reflection from Fe or Ni. Surface morphology of some samples studied by atomic force microscopy showed that the films are smooth and their typical surface roughness is 5 Å. Magnetoresistance measurements on the samples upto 20 kOe showed interesting results. The plots of magnetoresistance versus concentration showed maxima for certain concentration ranges and these values of maxima were found to be almost unaffected even when a large amount of Ni as high as 30% was present in the Cu grains.