Physics and Astronomy, Ames Laboratory
Journal or Book Title
Physical Review B
The anisotropic upper critical field, Hc2(T), curves for K0.8Fe1.76Se2 are determined over a wide range of temperatures down to 1.5 K and magnetic fields up to 60 T. Anisotropic initial slopes of Hc2 ~ −1.4 T/K and −4.6 T/K for magnetic field applied along c axis and ab plane, respectively, were observed. Whereas the c axis Hcc2 (T) increases quasilinearly with decreasing temperature, the ab plane Habc2(T) shows a flattening, starting near 25 K above 30 T. This leads to a nonmonotonic temperature dependence of the anisotropy parameter γH≡ Habc2/Hcc2. The anisotropy parameter is ~2 near Tc~32 K and rises to a maximum γH~ 3.6 around 27 K. For lower temperatures, γH decreases with T in a linear fashion, dropping to γH~2.5 by T~18 K. Despite the apparent differences between the K0.8Fe1.76Se2 and (Ba0.55K0.45)Fe2As2 or Ba(Fe0.926Co0.074)2As2, in terms of the magnetic state and proximity to an insulating state, the Hc2(T) curves are remarkably similar.
American Physical Society
Mun, Eundeok D.; Altarawneh, M. M.; Mielke, C. H.; Zapf, V. S.; Hu, Rongwei; Bud’ko, Sergey L.; and Canfield, Paul C., "Anisotropic Hc2 of K0.8Fe(1.76)Se(2) determined up to 60 T" (2011). Physics and Astronomy Publications. 679.