SUPERPARAMAGNETIC BEHAVIOR AND GIANT MAGNETORESISTANCE IN AS-OBTAINED CO-AG METASTABLE ALLOYS

The correlation between the structure and the magnetic and magnetotransport properties of metastable alloys CoxAg100-x (14 less-than-or-equal-to x less-than-or-equal-to 62), obtained by magnetron sputtering, are investigated as function of the Co content, x. The as-obtained samples 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, where the increase with the Co content of the mean grain diameters of the Co-rich metastable clusters responsible for the observed superparamagnetism, 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, exchange anisotropy effects are detected for the higher values of x as a consequence 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 temperature, respectively.