Giant magnetoresistance in melt-spun Co-Cu modified by rare earths

Samples of the composition RExCo20Cu80-x, RE = Sm, Gd or Dy (x = 0, 1, and 3) were produced by melt-spinning and subsequent annealing. The magnetoresi stance is negative as in granular Co-Cu, but its values depend on the kind of rare earth element added and on changes in the microstructure induced by thermal annealing. An addition of 1 at.% rare earth metal to Co20Cu80 yiel ds a considerable increase in the magnetoresistance ratio, whereas an addit ion of 3 at.% causes a decrease. E.g., by addition of 1 at.% Dy to Co20Cu80 and optimal thermal treatment, the value of magnetoresistance ratio measur ed at 10 K in a field of 5 T increases from -14% to -28%. The effect can be attributed to the presence of clusters of hexagonal Dy(Co,Cu)(5), which wa s ascertained from X-ray diffraction data, or other, metastable rare-earth compounds and paramagnetic rare-earth atoms in the Cu matrix.