The relation between giant magnetoresistance ͑GMR͒ and phase separated nanostructures in Cu 90 Co 10 is studied using magnetotransport measurements together with transmission electron microscopy and x-ray microanalysis. The samples were melt-spun ribbons isochronally annealed up to 873 K, and all show in their grains a homogeneous spinodal decomposition characterized by long parallel Co-excess stripes. These stripes have 40-nm modulation periods and develop along the crystalline directions of each grain. Different anneals do not change appreciably the observed microstructures, while the magnetoresistance is initially enhanced by a factor of 2, followed by a 35% drop above 823 K. The latter coincides with the observation of a secondary lamellar decomposition of 4 nm modulation length. We propose that the GMR effects in CuCo alloys originate from these nanoscopic modulations of the constituents induced by nonequilibrium processes.

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The classical model of independent random single deformation faults and twin faulting in face-centered-cubic and hexagonal close packing is revisited. The model is extended to account for the whole range of faulting probabilities. The faulting process resulting in the final stacking sequences is described by several equivalent computational models. The probability sequence tree is established. Random faulting is described as a finite-state automaton machine. An expression giving the percent of hexagonality from the faulting probabilities is derived. The average sizes of the cubic and hexagonal domains are given as a function of single deformation and twinning fault probabilities. An expression for the probability of finding a given sequence within the complete stacking arrangement is also derived. The probability P(0)(Delta) of finding two layers of the same type Delta layers apart is derived. It is shown that previous generalizations did not account for all terms in the final probability expressions. The different behaviors of the P(0)(Delta) functions are discussed.