GMR effect in Co-Cu microwires

We studied magnetic properties and GMR effect of Co-x - Cu100-x (10 a parts per thousand currency sign x30 at%) microwires. We observed considerable magnetoresistance (MR), Delta R/R, in Co-Cu glass coated microwires with x = 10-30%. For low x content (x = 10), Delta R/R we observed negative MR, tending to saturate in high magnetic fields, H. On the other hand, for the samples x = 30 Delta R/R(H) dependences showed non-monotonic behavior, exhibiting Delta R/R increase with H at low H-values (up to 5 kOe) and also considerable GMR effect. Temperature dependence of magnetization measured in samples cooled without magnetic field (zero field cooling, ZFC) and cooled under magnetic field (field cooled, FC) exhibit significant difference for Co (x) Cu100-x (x = 30). For Co (x) Cu100-x (x = 10) microwires we observed a maximum at quite low temperature, indicating possibility of existence of some amount of small Co-grains. X-ray diffraction (XRD) results reveal that the structure of the metallic core is granular with two phases: the main one, fcc Cu (lattice parameter 3.61 ), found in all samples and fcc alpha-Co (lattice parameter 3.54 ) which is present in microwires with higher Co content. In the case of low Co content, XRD indicates that Co atoms are distributed within the Cu crystals. The quantity and the crystallite size of the formed phases strongly depend on the geometry of the microwire.