Mössbauer spectroscopy and magnetometry of FeCo-Ag and FeCo-Au nanocomposites synthesized by a redox-transmetalation method

Composite nanoparticles (NPs) of FeCo-Ag and FeCo-Au fabricated by the redox-transmetalation technique are characterized by transmission electron microscopy (TEM), X-ray diffractometry (XRD), Mössbauer spectroscopy and magnetometry. TEM images prove the formation of agglomerated quasi-spherical NPs with mean value of diameter about 28 nm. As indicated by XRD and Mössbauer spectroscopy composite NPs constitute cores containing Fe3+Co-based oxides with smaller contribution of bcc α-FeCo alloy and shells representing well crystallized Ag and Au. Mean value of diameters of magnetic cores (≈10 nm) and non-magnetic shells (≈18 nm) in composite NPs are estimated by complementary analysis of TEM images, broadening of XRD reflections and approximation of hysteresis curves M(H) with Langevin function.