Tetragonal magnetic phase in Ba1-x KxFe2As2 from x-ray and neutron diffraction

In this paper, combined neutron and x-ray diffraction experiments demonstrate the formation of a low-temperature minority magnetic tetragonal phase in Ba 0.76K 0.24Fe 2As 2 in addition to the majority magnetic, orthorhombic phase. The coincident enhancement in the magnetic (1/2 1/2 1) peaks shows that this minority phase is of the same type that was observed in Ba 1-xNa xFe 2As 2 (0.24 ≤ x ≤ 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. Finally, the observations suggest that in this regime the energy levels of the C 2 and C 4 symmetric magnetic phases are very close.