  We report successful fabrication of multi- and mono-core FeSe wires with high
transport critical current density Jc using a simple in-situ Fe-diffusion
process based on the powder-in-tube (Fe-diffusion PIT) method. The seven-core
wire showed transport Jc of as high as 1027 A/cm2 at 4.2 K. The superconducting
transition temperature Tczero was observed at 10.5 K in the wire-samples, which
is about 2 K higher than that of bulk FeSe. The Fe-diffusion PIT method is
suitable for fabricating multi-core wires of the binary FeSe superconductors
with superior properties.
