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$_2$ ($0.24 \leq x \leq 0.28$), 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.
Categories: cond-mat.supr-con