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Abstract:
Iron selenide, Fe1.01Se, the layered parent compound of the recently
discovered superconducting arsenide family, has previously been shown to
be non-magnetic and superconducting with a critical temperature of 8 K.
Here we show that copper can be substituted at the iron site in Fe1.01Se
up to a solubility limit of 20-30%, after which a first-order transition
to the three-dimensional CuFeSe2 structure type is observed. As little
as 1.5% copper is sufficient to suppress the superconductivity, and 4%
drives the system through a metal-insulator transition. A local magnetic
moment is introduced, which maximizes near 12% doping, where a
spin-glass transition near 15 K is observed.
