Magnetization studies of K <inf>0.8</inf>Fe <inf>1.7</inf>Se <inf>2</inf> single crystals

Magnetization measurements of the magnetosuperconducting K 0.8Fe 1.7Se 2 single crystals (TC = 29.6 K) at various applied fields and temperatures have been performed. In the superconducting range, two unusual phenomena are observed. (i) The presence of paramagnetic Meissner effect up to 20 Oe, which is revealed by the positive field-cooled magnetization curves. (ii) A double peak in the hysteresis loop at low temperatures. The isothermal magnetization measured at 35 K clearly indicates the presence of a tiny amount of a ferromagnetic substance (probably pure Fe). The two peculiar phenomena observed are attributed to this impurity. © 2011 Springer Science+Business Media, LLC