Structure, superconductivity and magnetic properties of mechanically alloyed Mg1 − xFexB2 powders with x=0–0.4 Original Research Article

Mechanical milling of Mg1 − xFexB2 with x=0–0.4 led to the formation of amorphous phase. For x=0, the hexagonal MgB2 phase was formed after a heat treatment at 450 °C or above with critical temperature Tc=38–40 K. Fe-substituted MgB2 phase was formed after annealing at 450 °C or above when x=0.05, 0.1 and 0.2. Fe solubility in the MgB2 phase decreased with increasing annealing temperature, while lattice parameters (a and c) decreased. It has been found that critical temperature Tc increased with increasing annealing temperature. For Mg0.6Fe0.4B2 powder, MgB2 phase could not be formed after crystallization. Single solid-solution MgB2 phase could be formed in Mg0.95Fe0.05B2 after annealing at 450 °C. This sample exhibited paramagnetic between 30 and 290 K with a high magnetic moment of μFe=5.5–6.0μB. An anomaly (minimum in reciprocal magnetic susceptibility) was observed below 30 K, accompanied by magnetic splitting in Mössbauer spectroscopy.