Exchange bias and superspin glass behavior in nanostructured CoFe2O4 - Ag composites

We have prepared the (CoFe2O4)(100-x)Ag-x with x = {35, 60 and 75} wt. % nanocomposites, and report the superspin glass behavior of sample with x = 75 wt.%. The samples were analyzed by X-ray diffraction, transmission electron microscopy, AC susceptibility, DC magnetometry and Mossbauer spectroscopy. The DC magnetic measurements were performed from 4 K to 900 K. The Mzfc curves show a peak at T-max increasing from 200 K to 470 K when Ag concentration decreases from 75 wt. % to 35 wt. %. For sample with x = 75 wt. %, the in phase AC susceptibility data shows a superspin glass transition at T-g = 165 K. The out of phase AC susceptibility shows a peak at 42 K regarded to the spinglass transition of the particle's disordered surface. At 4 K, all samples show hysteresis loops with exchange bias behavior. A study done on the exchange bias field versus cooling field data for sample with x = 75 wt. %, shows a magnetic disordered layer with thickness of twice the lattice parameter of CoFe2O4.