Collective magnetic behaviors of Fe-Ag nanostructured thin films above the percolation limit

The magnetic behavior of sputtered and pulsed laser deposited (PLD) FexAg100-x thin films with 27 <= x <= 55 has been studied by means of ac and dc magnetic measurements. Sputtered samples present a continuous decrease in the magnetization, down to 310 K for x=30, where a magnetic transition into a superparamagnetic state with the presence of dipolar interactions is observed. The ac susceptibility measurements indicate that this transition resembles that of three dimensional glassy systems. Sputtered samples with higher concentration of Fe present a similar but slower thermal evolution of magnetization. PLD samples with x >= 50 show a Curie-Weiss-type transition above similar to 200 K triggered by direct exchange interactions. As the temperature decreases, the system behaves like a ferromagnet and below similar to 75 K, a transition into a cluster-glass state appears. As the composition decreases, these phenomena vanish. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3067430]