First-principles Study On Electronic And Magnetic Properties Of Iron Fluoride Materials

Computational Physics causes more and more physics researchers'interesting because of its incomparable advantages beyond experimental physics.The first-principles calculation has been used to predicate the physical properties of materials and design materials.In this paper,I studied the electronic properties of the strongly correlated systems by using the first-principles code VASP?Vienna Ab-inito Simulation Packagey?.Via first-principles calculations based on density functional theory,we have studied the structural evolution,electronic and magnetic properties of the high-pressure perovskite phase InFeO₃?orthorhombic,space group Pnma?,and focused on the multiferroic properties of the LiNbO₃-type InFeO₃?rhombohedral,space group R3c?.First-principles calculations have been used to investigate the structural,electronic as well as magnetic properties of a new charge-ordered iron fluoride material,K₄(Fe²⁺)(Fe³⁺)₂F₁₂,within a layered perovskite-related structure.Our results established that K₄Fe₃F₁₂2 is a Mott-Hubbard insulator,and adopts a magnetically ground state where the Fe²⁺and Fe³⁺spins are arranged in an approximately antiparallel manner to each other,in agreement with the experimental observations.Although the total 3d charge disproportion is rather small,an order parameter,defined as the difference between the dz²orbital occupations of the the Fe³⁺and Fe²⁺cations,provides explicit evidence on the charge ordering.Furthermore,the unique occupation of the dz²orbital is responsible for the stability of the antiferromagnetic spin ordering and the charge ordering pattern.The structural,electronic and magnetic properties of a charge-ordered iron fluoride material CsFe²⁺Fe³⁺F₆ have been explored by the density functional theory calculations based on the generalized gradient approximation?GGA?+U approach,which was implemented in the VASP code.The material exhibits a three-dimensional pyrochlore-related structure which consists of corner-shared Fe²⁺F₆ and Fe³⁺F₆ octahedra.Our results confirmed that CsFe₂F₆ is a Mott-Hubbard insulator,and bears a magnetically frustrated ground state in which the localized 3d electrons are antiferromagnetically coupled between the homogeneous Fe ions(Fe³⁺-Fe³⁺along the b axis,and Fe²⁺-Fe²⁺along the a axis),while the interactions between the heterogeneous Fe ions(Fe³⁺-Fe²⁺along the c axis)are frustrated,in consistent with the Goodenough-Kanamouri superexchange interactions.Although the disproportionation of total 3d charge is extremely small,the explicit evidence was provided on the charge ordering by an order parameter,which was defined as the difference of minority d_yzz orbital?in the local coordinates?occupations between the Fe³⁺and Fe²⁺cations.In addition,the spin ordering and spin-orbit coupling effect play an insignificant role in the charge ordering and the preferential occupation of the d_yzz orbital scenario in CsFe₂F₆.