Size distribution and interaction effects on dispersed Fe30Ni70 nanoalloy synthesized by thermal decomposition

•Nanoparticles.•TEM.•RAM.•Magnetism. Magnetic properties of Fe30Ni70 nanoalloys dispersed in a silica matrix are reported. X-ray diffraction patterns and TEM images are consistent with a fcc crystalline structure (space group Fm3m). Thermogravimetric data and its derivative reveal important features about the kinetics formation of the nanoalloy. Magnetization data as a function of an applied magnetic field and temperature indicate that nanoalloys are superparamagnetic with blocking effects appearing around T = 10 K. However, the unusual magnetic-field-dependence of the blocking temperature suggests that interaction effects must be taken into account. In this sense, as the power law usually employed to describe noninteracting particles system do not fit our experimental data, we have used a simple modification of the random anisotropy model (RAM). Finally, once the size distribution of nanoparticles should also play a crucial role in determining the magnetic behavior of the sample, we have analyzed the T-dependence of coercive field using a generalized model, which takes into account this parameter.