Effects of thermal annealing on the magnetic interactions in nanogranular Fe–Ag thin films

In this paper we have studied, by analysing the evolution of the magnetic behaviour during thermal treatment, the role of the interparticle magnetic interactions in FexAg100−x granular thin films prepared by sputtering deposition technique. Two compositions have been selected: x = 25 and 35, below and around the magnetic percolation of the system, respectively, according to our previous works. The structure of these thin films has been studied by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) measurements. To analyse the magnetic behaviour, DC magnetic measurements have been carried out after progressively annealing the samples at different temperatures (0 ≤ Tann ≤ 200 °C). These measurements have revealed that, upon thermal treatment, the frustrated state at low temperatures (T < 80 K) for the x = 25 sample tends to disappear, probably due to the weakening of RKKY interactions after the segregation of soluted Fe atoms in the Ag matrix. However, dipolar interactions are not affected by the annealing. On the contrary, at x = 35, around the magnetic percolation, the annealing gives rise to an increasingly ordered interface, thereby enhancing the transfer of the direct exchange interactions.

► FexAg100−x granular thin films with competing interactions (25 ≤ x≤ 35). ► Annealing up to 200 °C mainly modifies the interface of Fe nanoparticles. ► Annealing reduces RKKY interactions in Fe25Ag75. ► Annealing favors exchange interactions and ferromagnetic order in Fe35Ag65.