Superconductivity in PbO-type tetragonal FeSe nanoparticles

The existence of a high-temperature superconducting phase with TcTc∼40 K in PbO-type tetragonal ββ-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 ββ-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.

► In this paper we describe the development of a simple, rapid process to synthesize superconducting ββ-FeSe nanoparticles.
► The crystal structure of the nanoparticles obtained has the same PbO-type tetragonal symmetry as the bulk sample.
► Magnetic susceptibility measurements show that all nanoparticles are superconducting, with the major phase having TcTc∼10 K.
► The most important result is the observation of a superconducting-like transition with onset at ∼40 K in the FeSe nanoparticles.