Orbital ordering and magnetic interactions in BiMnO₃

Abstract

Abstract. This work is devoted to the analysis of the orbital ordering patterns and associated interatomic magnetic interactions in the centrosymmetric monoclinic structures of BiMnO 3 , which have been recently determined experimentally. First, we set up an effective lattice fermion model for the manganese 3d bands and derive parameters of this model from first-principles electronic structure calculations. Then, we solve this model in terms of the mean-field Hartree-Fock method and obtain parameters of interatomic magnetic interactions between Mn ions. We argue that although the nearest-neighbor interactions favor the ferromagnetism, they compete with the longer range antiferromagnetic (AFM) interactions, the existence of which is directly related to the peculiar geometry of the orbital ordering pattern realized in BiMnO 3 below 474 K. These AFM interactions favor an AFM alignment, which breaks the inversion symmetry. The formation of the AFM phase is additionally assisted by the orbital degrees of freedom, which tend to adjust the nearest-neighbor magnetic interactions in the direction which further stabilizes this phase. We propose that the multiferroelectric behavior, which was observed in BiMnO 3 , may be related to the emergence of the AFM phase under certain conditions.

Long-Range Magnetic Interactions Induced by the Lattice Distortions and the Origin of the E-Type Antiferromagnetic Phase in the Undoped Orthorhombic Manganites

“…For example, in BiMnO 3 such a mechanism facilitates the formation of the "##" AFM structure, which breaks the inversion symmetry. 16) Nevertheless, in RMnO 3 the situation appears to be different. For all considered compounds, the NN interactions calculated in the E-phase satisfy the following condition: J k 1 ð""Þ < J k 1 ð"#Þ, where the notations "" and "# are referred to the FM and AFM bonds, respectively (Fig.…”

“…16,27,31) After the solution for each magnetic state, the total energy changes corresponding to infinitesimal rotations of the spin magnetic moments near this state were mapped onto the Heisenberg model: 34,35) E Heis ¼ À 1 2…”

Structural and Electronic Properties of Bixo&lt;sub&gt;3&lt;/sub&gt; (X = Mn, Fe, Cr)

“…Therefore the origin of ferroelectricity in these two compounds seems to be different. In BiMnO 3 the emergence of electric moment is connected with inversion symmetry breaking by the AFM order induced by particular orbital order below T = 474 K [42,43]. Another scenario for the onset of electric moment is possible in BiFeO 3 : an extensive investigation of ferroelectricity in BiFeO 3 in the framework of density functional theory was reported in reference [44].…”

Specific features of magnetic structure formation in orbitally degenerate BiMnO3 manganite

“…However, the results of recent experiments [7,8] have shown that this ferromagnetic crystal belongs to the C2/c symmetry group, which excludes the exist ence of spontaneous polarization [5][6][7][8][9]. External fac tors (temperature, pressure) can alter the magnetic structure of BiMnO 3 crystals so as to stabilize antifer romagnetism [8,9].…”

“…Bismuth manganite BiMnO 3 has been treated in many investigations as a multiferroelectric compound [1][2][3][4][5][6]. However, the results of recent experiments [7,8] have shown that this ferromagnetic crystal belongs to the C2/c symmetry group, which excludes the exist ence of spontaneous polarization [5][6][7][8][9].…”