Coexistence of short- and long-range ferromagnetic order in nanocrystalline Fe2Mn1−Cu Al (x=0.0, 0.1 and 0.3) synthesized by high-energy ball milling

Abstract In this work, we prepared nanocrystalline Fe 2 Mn 1− x Cu x Al ( x =0.0, 0.1 and 0.3) powders by the high energy ball milling technique, and then studied their critical properties. Our analysis reveals that the increase of Cu-doping concentration (up to x =0.3) in these powders leads to a gradual increase of the ferromagnetic–paramagnetic transition temperature from 406 to 452 K. The Banerjee criterion suggests that all the samples considered undergo a second-order phase transition. A modified Arrott plot and scaling analysis indicate that the critical exponents ( β =0.419 and 0.442, γ =1.082 and 1.116 for x =0.0 and 0.1, respectively) are located in between those expected for the 3D-Heisenberg and the mean-field models; the values of β =0.495 and γ =1.046 for x =0.3 sample are very close to those of the mean-field model. These features reveal the coexistence of the short- and long-range ferromagnetic order in the nanocrystalline Fe 2 Mn 1− x Cu x Al powders. Particularly, as the concentration of Cu increases, values of the critical exponent shift towards those of the mean-field model. Such results prove the Cu doping favors establishing a long-range ferromagnetic order.