In this paper, we report on synthesis and magnetic properties of dispersed Fe \(_x\) Ni \(_{1-x}\) (x = 10, 20, 30, 40, and 50) nanoalloys grown by thermal decomposition. X-ray diffraction patterns show that the majority crystalline phase is consistent with a fcc crystal structure (space group Fm3m) for all samples. Magnetization as a function of magnetic field and temperature shows that Fe \(_x\) Ni \(_{1-x}\) are superparamagnetic with blocking temperatures around 10 K. However, for all samples, it is possible to observe a second very broad maximum, which can be ascribed to a bimodal nanoparticle size distribution and/or Ni nanoparticles for the case of samples grown with x = 10, 20, and 30. Finally, we argue that the nanoalloy size distribution and/or interaction effects should play a crucial role in determining the magnetic behavior of samples once we are not able to fit our \(H_C\) (T) data using the Néel relaxation and the Bean-Livingston approaches in a wide temperature range.
