2008/05/16 by Hisashi Uzu, A. Tanaka, Arata Tanaka
Materials Science · Physics and Astronomy · #Advanced Condensed Matter Physics #Magnetic Properties and Synthesis of Ferrites #Multiferroics and related materials #cond-mat.mtrl-sci #cond-mat.str-el
paper · pdf · doi:10.1143/jpsj.77.074711
16 pages, 13 figures, 6 tables, accepted for publication in J. Phys. Soc. Jpn
arxiv created 2008/05/16 · openalex publication_date 2008/06/26 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
Electronic state and the Verwey transition in magnetite (Fe3O4) are studied using a spinless three-band Hubbard model for 3d electrons on the B sites with the Hartree-Fock approximation and the exact diagonalisation method. Complex-orbital, e.g., 1/sqrt(2)[|zx> + i |yz>], ordered (COO) states having noncollinear orbital moments ~ 0.4 muB on the B sites are obtained with the cubic lattice structure of the high-temperature phase. The COO state is a novel form of magnetic ordering within the orbital degree of freedom. It arises from the formation of Hund's second rule states of spinless pseudo-d molecular orbitals in the Fe4 tetrahedral units of the B sites and ferromagnetic alignment of their fictitious orbital moments. A COO state with longer periodicity is obtained with pseudo-orthorhombic Pmca and Pmc21 structures for the low-temperature phase. The state spontaneously lowers the crystal symmetry to the monoclinic and explains experimentally observed rhombohedral cell deformation and Jahn-Teller like distortion. From these findings, we consider that at the Verwey transition temperature, the COO state remaining to be short-range order impeded by dynamical lattice distortion in high temperature is developed into that with long-range order coupled with the monoclinic lattice distortion.