G -type magnetic order in ferropnictide CuxFe1−y

Breakdown of Hund's rule for CuFeAs

“…Furthermore, as was observed in experiments [24,26], CuFeAs is nonstoichiometric with Cu sites being partially va- cant. Cu vacancy will cause heavy hole doping and may alter crystal field splitting due to the deficiency of cations in certain positions.…”

“…1 (a) where various As heights reported in different experiments are shown, at h As less than h c , our theoretical calculations point to a CAFM ground state, which is mainly consistent with the experimental results where either long-range [23] or short-range [25] AF order was observed, though the magnetic structure has not been determined ex-perimentally yet. But, in the cases of h As greater than h c , while the theoretical ground state is strongly FM, it was inferred from experiments [22,24,26] that CuFeAs should be an antiferromagnet probably with ferromagnetic components. The contradiction raises a great challenge to the existing theory [34,42], which seems valid for the whole family of ironbased superconductors including both iron pnictides and iron chalcogenides, where various magnetic ground states can be correctly accounted for after different anion height is considered.…”

“…However, when h As is greater than h c , the FM state becomes the ground state owing to J 1 < −2J 2 and J 1 < −J 2 − 2J 3 . Since antiferromagnetism was observed in experiments [22,24,26] when h c < h As < 1.84Å, it indicates that local moment picture fails to account for the magnetic ground state of CuFeAs in the intermediate region of anion height.…”

“…The antiferromagnetism was further demonstrated by neutron diffraction experiments [24,25], where either an unusual G-type antiferromagnetic order or proximity to an antiferromagnetic instability was proposed. Though ferromagnetism was also reported in the literature [26,27], it was pointed out that the weak ferromagnetism probably comes from a ferromagnetic component of a canted antiferromagnetic state [24,26]. Therefore, while the type of antiferromagnetic order is still unclear, it seems conclusive that the ground state of CuFeAs is antiferromagnetic experimentally.…”

“…The magnetic susceptibility measurements showed that it is antiferromagnetic with Néel temperature T N of around 9 K [22,23]. The antiferromagnetism was further demonstrated by neutron diffraction experiments [24,25], where either an unusual G-type antiferromagnetic order or proximity to an antiferromagnetic instability was proposed. Though ferromagnetism was also reported in the literature [26,27], it was pointed out that the weak ferromagnetism probably comes from a ferromagnetic component of a canted antiferromagnetic state [24,26].…”