Magnetic properties and superconductivity of mechanically alloyed (Mg1−xFex)B2 samples with x=0.0–0.4

Abstract

In the current work, we have prepared and studied (Mg1−xFex)B2 samples with x=0.0–0.4 prepared by mechanical alloying and subsequent vacuum annealing. All the as-milled powders were found to be amorphous in x-ray diffraction examination and no superconductivity was evident until 4.2 K. The MgB2 phase was formed after a vacuum annealing at 450 °C or higher. For the pure MgB2 sample without Fe substitution, critical temperatures of 38–39 K was measured for the samples after heat treatment at 450 °C or higher. For Fe-containing samples (Mg1−xFex)B2 with x=0.05–0.2, the solubility of Fe in the MgB2 phase decreased with increasing annealing temperature as confirmed by x-ray diffraction and Mössbauer studies. Besides MgB2, other phases (α-Fe, Fe2B, and MgB4) were observed. The critical temperature Tc increased with increasing annealing temperatures, indicating that Tc decreased with increasing Fe concentration in the MgB2 phase. For (Mg0.6Fe0.4)B2, the MgB2 phase could not be formed after heat treatment and MgB4 and Fe2B were the major phases after crystallization. Superconductivity was not observed in the as-milled and subsequently annealed (Mg0.6Fe0.4)B2 specimens.