Preparation and characterisation of Os doped MgB2

• Polycrystalline osmium doped MgB2 samples were prepared by solid state route.
• Up to 1 at.% Mg can be replaced by Os in the MgB2 lattice.
• Tc decreases at a rate of 2.1 K/at.% Os upon doping.

Polycrystalline samples with Mg1−xOsxB2.04 nominal stoichiometry were made by reacting elemental powders at 800 °C under argon atmosphere. Based on XRD diffraction patterns, EDS analysis and magnetisation measurements, it is found that Os can replace up to about 1 at.% Mg in the MgB2 lattice. Beyond this doping level, unreacted Os and Mg-rich Mg–Os impurity phases are formed. The a-axis parameter contracts upon doping while the superconducting transition temperature decreases at a rate of 2.1 K/at.% Os substitution. At 10 K, Os doping induces an improvement of the normalised critical current density under applied magnetic fields in excess of 0.5 T, indicating a modest enhancement of flux pinning in this range.