Anisotropic Hc2 for the K0.8Fe1.76Se2 single crystals. Solid circles are obtained from the pulsed field radio frequency shift measurements and closed (open) square and triangle symbols are taken from temperature (magnetic field)-dependent resistance measurements. Inset shows the temperature dependence of the magnetic hyperfine field (Bhf). The solid line is a fit to a J=1/2 Brillouin function between 200 K and 500 K that yields an expected transition of 600 +- 30 K, well above the observed value of 532 +-2 K. The rapid collapse above 500 K is accompanied by the growth of a paramagnetic component.
Fe57 Mössbauer study of magnetic ordering in superconducting K0.80Fe1.76Se2.00 single crystals