SUPERPARAMAGNETIC BEHAVIOR AND GIANT MAGNETORESISTANCE IN AS-OBTAINEDCO-AG METASTABLE ALLOYS

The correlation between the structure and the magnetic and magnetotran sport properties of metastable alloys CoxAg100-x (14 less-than-or-equa l-to x less-than-or-equal-to 62), obtained by magnetron sputtering, ar e investigated as function of the Co content, x. The as-obtained sampl es show superparamagnetic behavior at room temperature for almost all the concentration range, with blocking temperatures increasing with x. Such behavior is a consequence of the granular nature of the films, w here the increase with the Co content of the mean grain diameters of t he Co-rich metastable clusters responsible for the observed superparam agnetism, is the origin of the dependence of the blocking temperature with x. The fitting of the experimental data to the Langevin function has allowed an estimation of the magnetic grain size. Moreover, exchan ge anisotropy effects are detected for the higher values of x as a con sequence of partial oxidation of the Co-rich particles. Finally, this granular structure generates the occurrence of giant magnetoresistance (GMR) with maximum values around 40% and 20% at low and room temperat ure, respectively.