Tetragonal magnetic phase in Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ from x-ray and neutron diffraction

Abstract

Combined neutron and x-ray diffraction experiments demonstrate the formation of a low-temperature minority tetragonal phase in Ba${}_{0.76}$K${}_{0.24}$Fe${}_2$As${}_2$ in addition to the majority magnetic, orthorhombic phase. A coincident enhancement in the magnetic ($\frac{1}{2}$ $\frac{1}{2}$ 1) peaks shows that this minority phase is of the same type that was observed in Ba${}_{1-x}$Na${}_x$Fe${}_2$As${}_2$ ($0.24\le x\le 0.28$), in which the magnetic moments reorient along the $c$-axis. This is evidence that the tetragonal magnetic phase is a universal feature of the hole-doped iron-based superconductors.

6 pages, 7 figures