Cálculos das propriedades eletrônicas e magnéticas da manganita multiferróica hexagonal HoMnO3

Abstract

In this work was performed a study based on density functional theory of the electronic and magnetic properties of the hexagonal multiferroic manganite HoMnO3. Were performed calculations with and without the inclusion of the spin-orbit interaction, using the full potential linearized augmented plane wave method. The exchange and correlation electronic effects were approximated via generalized gradient approximation (GGA) and the method "+ U" (or GGA + U). It is known that the magnetism in HoMnO3 is due to Mn 3d4- and Ho 4f10-states. In addition, exist a consensus that the magnetic order at Mn sub-lattice is non-collinear due to the triangular arranged of Mn magnetic moments () at a-b plane. In the case of Ho magnetic moments, the arrangement is collinear with parallel to c-axis. However, because of the complexity of crystalline symmetry and of the varieties of magnetic ions in the material, the literature has not yet reached a consensus on the magnetic ordering of them (antiferromagnetic-AFM, ferromagnetic-FM or a combination of the two), as well as the values. In this work, the main objectives were: (1) to determine the ground-state magnetic structure for Ho sub-lattice (2) to obtain the values of their respective , and (3) to describe the electronic structure of the compound. Considering the nine different magnetic structures simulated, four of them are shown with more details. These are the result of the combination of two possible configurations of spins collinear for the Mn (A type AFM, A-AFM, and G type, G-AFM) and two for the Ho (FM and AFM). It was observed that, among these, the lowest energy configuration is that for Mn is fixed according to the G – AFM type and the Ho in the A – AFM type. This result agrees with the prediction of experiments in respect of the order on the Ho sub-lattice, but the values of the magnetic moments did not agree. Was found that there is a close relationship between the simulated magnetic order and its electronic structure. In particular, the band gap for the magnetic orders less energetically favorable tends to leave the compound with metallic character which is not experimentally expected. The HoMnO3 is a semiconductor whose optical gap is about 1.7 eV. Using an U = 3.0 eV on 3d and 4f states of the Ho, we obtained an energy band gap of 1.29 eV. To analyze the electronic structure in more detail, was computed the total and partial states of compound, where it was possible to notice that the 4f states of Ho are localized predominantly at the top and bottom of conduction band which are hybridized with O’s 2p states.