Nanoscopic transformations and GMR in bulk non-equilibrium Cu–Co alloys

We have investigated ribbons of the alloy series Cu 1− x Co x ( x=0.05, 0.10, 0.15, and 0.20) using transmission electron microscopy and magnetotransport measurements to correlate nanostructural transformations to its giant magnetoresistance (GMR) behavior. Instead of dealing with a simple granular system, as it is commonly assumed, we show that spinodal decomposition in the form of lamellar phases is in fact the common feature observed in these materials, and that GMR is seen whenever this decomposition is observed. The formation of these nanoscopic lamellae as metastable segregated phases can be understood via a Cahn–Hilliard analysis.