Correlation effects among nanometre-sized clusters in Cu-Co melt-spun alloys with giant magnetoresistance

Magnetic correlation effects in nearly superparamagnetic granular Cu100-xCox systems exhibiting giant magnetoresistance (GMR) are studied by analysing the flat-top parabolae obtained when the GMR is plotted as a function of reduced magnetization. The nature of GMR in granular metallic systems is discussed in detail, taking into account the typical time constants involved in the short-time dynamics of magnetic moments in a local magnetic field. An outline of a theory providing the first quantitative explanation of the effect of magnetic correlation on GMR is given. The role of Co content in the sizes and distances of Co particles and in their degree of magnetic correlation are discussed, examining, for studied composition each, the samples characterized by the best GMR values.