Study of dynamic behaviors for nano Fe-doped MgB2 superconductor via ac-susceptibility measurements

Nano-sized superconducting polycrystalline particles of Mg1-xFexB2 (0.00 <= x <= 0.04; space group P6/mmm) were synthesized through the solid state reaction route. The effect of nano-Fe substitution on ac-susceptibility at varying frequency range from 1 to 3 kHz in addition with ac-amplitude (H-ac) and dc-applied field (H-dc) were explored. The dynamical behavior of nano-particles shows the strong magnetic interaction between the nano clusters with the increase of doping content. This is due to the successful inclusion of Fe3+ ions in the matrix of MgB2, X-ray powder diffraction (XRD) reveals the reduction of average grain size with increasing the doping level. Neel-Arrhenius (N-A) and Vogel-Fulcher (V-F) models were discussed to distinguish the dynamical behaviors of the nano-particles. Remarkably, the V-F model elucidates the experimental results much better than N-A model with the support of some parameters like jump attempt frequency, activation energy, magnetic anisotropy constant and V-F temperature.