Charge ordering and magnetic frustration in CsFe2F6. (28th June 2017) - Liu, Shanshan
Abstract: The structural, electronic and magnetic properties of a charge-ordered iron fluoride material CsFe 2+ Fe 3+ F6 have been explored by density functional theory calculations based on the generalized gradient approximation + U approach, which was implemented in the VASP code. The material exhibits a 3D pyrochlore-related structure which consists of corner-shared Fe 2+ F6 and Fe 3+ F6 octahedra. Our results confirm that CsFe2 F6 is a Mott–Hubbard insulator, and bears a magnetically frustrated ground state in which the localized 3 d electrons are antiferromagnetically coupled between the homogeneous Fe ions (Fe 3+ –Fe 3+ along the b axis, and Fe 2+ –Fe 2+ along the a axis), while interactions between the heterogeneous Fe ions (Fe 3+ –Fe 2+ along the c axis) are frustrated, consistent with Goodenough–Kanamori superexchange interactions. Although the disproportionation of the total 3 d charge is extremely low, explicit evidence is provided on the charge ordering by an order parameter, which is defined as the difference in minority d yz orbital (in the local coordinates) occupations between the Fe 3+ and Fe 2+ cations. In addition, spin ordering and the spin–orbit coupling effect play an insignificant role in the charge ordering and the preferential occupation of the d yz orbital scenario in CsFe2 F6 .