Magnetic and structural transitions in the iron-chalcogenide high-Tc superconductor: K0.8Fe1.76Se2.00

57Fe Mössbauer spectroscopy was used to study single-crystals of K0.8Fe1.76Se2.00 from 6K to 673 K. At 6 K, the hyperfine field (Bhf) is canted away from the c-axis by 18±3°. The temperature dependence of Bhf follows a spin wave model with a spin excitation gap of 9±1 meV. A sudden increase in the line width and a corresponding drop in (1/2)eQVzz at TN = 532 K are indications of strong coupling between the magnetic and structural transitions