Superconductivity in PbO-type tetragonal FeSe nanoparticles

The existence of a high-temperature superconducting phase with T c ∼40 K in PbO-type tetragonal β -FeSe has been demonstrated by application of high pressure. We have used a rapid, solvent-less reaction under autogenic pressure at elevated temperature (RAPET) process to synthesize superconducting Fe–Se nanoparticles. The nanoparticles obtained are mainly the superconducting β -FeSe phase. Detailed magnetization measurements on these nanoparticles show that in addition to the superconducting transition at ∼10 K, we observe an anomaly in magnetic susceptibility measurements suggesting the presence of a superconducting transition at ∼30 K in the synthesized nanoparticles. The superconducting volume fraction depends on the chemical composition of the starting materials and also on the processing time.