First principles study of the magnetic properties of LaOMnAs

Abstract

Recent experiments reported giant magnetoresistance at room temperature in LaOMnAs. Here a density functional theory calculation is performed to investigate magnetic properties of LaOMnAs. The ground state is found to be the G-type antiferromagnetic order within the ab plane but coupled ferromagnetically between planes, in agreement with recent neutron investigations. The electronic band structures suggest an insulating state which is driven by the particular G-type magnetic order, while a metallic state accompanies the ferromagnetic order. This relation between magnetism and conductance may be helpful to qualitatively understand the giant magnetoresistance effects.Since the discovery of high-temperature superconductivity in fluorine-doped LaOFeAs, 1 several Fe-based pnictide and chalcogenide compounds have been systematically studied.2-5 Recently, the Mn-based oxypnictides ROMnAs (R is a rare earth, e.g. La, Nd, Sm) that present a similar crystal structure as the materials mentioned above have also been synthesized and studied experimentally.6-13 In contrast to their Fe-based cousins, at least until now these Mn-based oxypnictides have not shown any evidence of superconductivity even in doped cases. Instead, giant or even colossal magnetoresistance effects at room temperature have been observed in these compounds, 10-13 which reminds us of the well-known phenomenology of the colossal magnetoresistive manganites (Mn-based oxides) with the perovskite structures.14 Neutron studies have revealed that the magnetic ground state of ROMnAs is different from the isostructural ROFeAs.8,13 Different from the isostructural LaOFeAs which owns a stripe-like antiferromagnetic (AFM) state (as in the CA one shown in Fig. 1), ROMnAs shows a conventional in-plane G-type AFM order where all NN spins are antiparallel in-plane.13 This magnetic order is also different from magnetic orders in other Fe-based pnictides and chalcogenides, e.g. the bistripe AFM order found in FeTe 15 and the block-AFM order predicted in KFe 2 Se 2 . 16To understand the basic physical properties of ROMnAs, here we perform a density functional theory (DFT) calculation to investigate the electronic structures of LaOMnAs, especially its magnetic properties. Theoretically, LaOMnAs is simpler than NdOMnAs and SmOMnAs within the DFT framework since La 3+ is nonmagnetic (NM). Fortunately, the most attractive properties of ROMnAs, e.g. its magnetoresistive, does not rely on the magnetism of the rare-earth component. Thus, the undoped LaOMnAs provides a good starting point to study the exotic giant (or colossal) magnetoresistance of ROMnAs. Although Xu et al. have already conducted a pioneer DFT calculation on LaOM As (M =V-Cu), 17 the real LaOMnAs compound was experimentally studied in detail two years later.11 Thus, there are some nonnegligible differences between the early DFT predictions and the experimentally unveiled facts, such as the lattice constants.Later, a DFT calculation by Kayanuma et al. emphasized the band gap of LaOMnX (X=P, As, and Sb) but did not...

Topological magnetic phase inLaMnO3(111) bilayer

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Importance of effective dimensionality in manganese pnictides

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(LaTiO3)n/(LaVO3)n as a model system for unconventional charge transfer and polar metallicity

“…A 7 × 7 × 5, 5 × 7 × 7 and 7 × 7 × 5 Monkhorst-Pack k-point mesh centered at Γ point are adopted for ( The Hubbard repulsion U eff (= U − J) is imposed on Ti's/V's 3d and La's 4f orbitals using the Dudarev implementation [26]. According to previous literature [27][28][29], U eff (Ti)=2.3 eV, U eff (V)=3 eV, and U eff (La)=8 eV are proper to reproduce the experimental properties and thus are adopted as default parameters in the following calculations, if not noted explicitly.…”