Influence of magnetic interactions on magnetic and magnetoresistive properties of Cu80Fe10Ni10 ribbons

Magnetic and magnetotransport properties measurements of Cu80Fe10Ni10 (at. %) melt spun and annealed ribbons were combined to study the magnetic interactions present in this system. Those ribbons are composed of magnetic FeNi rich precipitates embedded in a nonmagnetic Cu rich matrix. When the precipitates are small enough, they have a superparamagnetic behavior. Upon annealing the precipitates get larger and progressively turn ferromagnetic. The relatively high magnetoresistive properties are attributed to the presence of those superparamagnetic precipitates. Using Mossbauer spectrometry, Zero Field Cooled/Field Cooled and magnetization curves, the presence of interactions among the precipitates was evidenced, which degrades the magnetoresistance properties. Using Allia model, the magnetic coherence length R-m between the precipitates was calculated and compared with the mean free path of the electrons lambda, with the precipitates size and the mean distance between them. Three different regimes were observed. At high fields, where R-m < lambda, meaning that the precipitates are not interacting, at smaller fields, where R-m > lambda and the precipitates are in the so called "interacting superparamagnetic regime," and at low fields, and at 5 K, R-m > 10 lambda, the magnetic interactions among the precipitates are strong and give rise to a hysteresis on the magnetization curves. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3117217]