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Describes ligand field splitting in terms of density functional theory. Association of split levels with the subterms of 4f[sup n-1]6s[sup 2] (n=3-14) configurations of lanthanide monofluorides; Relationship between multiplet splitting and single-determinant energies; Factors attributing the efficacy of ligand potential.

Investigates the formulated method to calculate split levels of spectroscopic subterms of lanthanide irons under the weak field coupling scheme. Application of the density functional theory and ligand field theory; Removal of the 4f-electron contribution from the potential; Introduction of pseudopotentials.

By extending our general spin-current model to noncentrosymmetric spin dimers and performing density functional calculations, we investigate the causes for the helical magnetic order and the origin of the giant ferroelectric polarization of CaMn7O12. The giant ferroelectric polarization is proposed to be caused by the symmetric exchange striction due to the canting of the Mn4+ spin arising from its strong Dzyaloshinskii-Moriya interaction. Our study suggests that CaMn7O12 may exhibit a novel magneto-electric coupling mechanism in which the magnitude of the polarization is governed by the exchange striction, but the direction of the polarization by the chirality of the helical magnetic order. [ABSTRACT FROM AUTHOR]

The olivine-type compounds LiMPO4 (M = Mn, Fe, Co, Ni) consist of MO4 layers made up of corner-sharing MO6 octahedra of high-spin M2+ ions. To gain insight into the magnetic properties of these phosphates, their spin exchange interactions were estimated by spin dimer analysis using tight binding calculations and by electronic band structure analysis using first principles density functional theory calculations. Three spin exchange interactions were found to be important for LIMPO4, namely, the intralayer superexchange J1, the intralayer super-superexchange Jb along the b-direction, and the interlayer super-superexchange J2 along the b-direction. The magnetic ground state of LIMPO4 was determined in terms of these spin exchange interactions by calculating the total spin exchange interaction energy under the classical spin approximation. In the spin lattice of LiMPO4, the two-dimensional antiferromagnetic planes defined by the spin exchange J1 are antiferromagnetically coupled by the spin exchange J2, in agreement with available experimental data. [ABSTRACT FROM AUTHOR]

On the basis of density functional calculations we explored the possibility that BN and ZnO single layers can become ferromagnetic at room temperature and half-metallic upon fluorine adsorption. Fluorine atoms form stable bonds only with the B and Zn atoms on the graphenelike BN and ZnO single layers, respectively, and the resulting fluorinated BN and ZnO single layers are expected to become ferromagnetic half metals with Curie temperatures around room temperature. The fluorination of semiconductor single layers can lead to interesting spintronics and functional applications. [ABSTRACT FROM AUTHOR]

Room-temperature ferromagnetism occurs in GaN nanoparticles even without any doped magnetic ions. The cause for this finding was examined by performing density functional calculations for the bulk GaN and the nonpolar surface of GaN with Ga- and N-vacancies. Our work indicates that the room-temperature ferromagnetism of undoped GaN nanoparticles originates from the nitrogen dangling bonds associated with the surface Ga-vacancies. The spins of the nitrogen dangling bonds couple ferromagnetically by through-bond spin polarization, and this ferromagnetic coupling is effective even when the vacancy separation is as long as ∼8 Å. [ABSTRACT FROM AUTHOR]

We report a detailed density functional analysis of the spin exchange interactions and the magnetic structure of the high-temperature multiferroic CuBr2 and compare the results with magnetic susceptibility measurements. CuBr2 shows one-dimensional antiferromagnetism and undergoes long-range antiferromagnetic ordering at ~74 K. Due to the competition between the nearest- and next-nearest-neighbor spin exchanges, each Cu2+ chain has a cycloidal spin-spiral structure, which is described approximately by a quadrupling of the nuclear cell with spin moment rotation of ~85° in the plane of the CuBr² ribbon plane. [ABSTRACT FROM AUTHOR]

The electronic and magnetic properties of spin-1/2 pyrochlores R2V2O7 were investigated on the basis of density-functional calculations. Contrary to common belief, the spin-1/2 V4+ ions are found to have a substantial easy-axis single-ion anisotropy. We show that the magnon quantum Hall effect of Lu2V2O7 is a combined consequence of the easy-axis single-ion anisotropy and the Dzyaloshinskii-Moriya interaction of the spin-1/2 V4+ ions. We also show that the negative magnetoresistance observed for R2V2O7 arises from a different mechanism, i.e., the band gap decreases as the spin alignment becomes more parallel to each other. [ABSTRACT FROM AUTHOR]

The discovery of superconductivity in the 122 iron selenide materials above 30 K necessitates an understanding of the underlying magnetic interactions. We present a combined experimental and theoretical investigation of magnetic and semiconducting Ce2O2FeSe2 composed of chains of edge-linked iron selenide tetrahedra. The combined neutron diffraction and inelastic scattering study and density functional calculations confirm the ferromagnetic nature of nearest-neighbor Fe-Se-Fe interactions in the ZrCuSiAs-related iron oxyselenide Ce2O2FeSe2. Inelastic measurements provide an estimate of the strength of nearest-neighbor Fe-Fe and Fe-Ce interactions. These are consistent with density functional theory calculations, which reveal that correlations in the Fe-Se sheets of Ce2O2FeSe2 are weak. The Fe on-site repulsion UFe is comparable to that reported for oxyarsenides and K1-xFe2-ySe2, which are parents to iron-based superconductors. [ABSTRACT FROM AUTHOR]

On the basis of single-crystal x-ray diffraction we show that TiPO4 undergoes a spin-Peierls distortion below 74.5(5) K, with a dimerization of the Ti chains along the c axis. Between 74.5(5) and 111.6(3) K, TiPO4 develops an incommensurate (IC) phase with temperature-dependent q vector (σ1 ,0,0). Density functional calculations strongly suggest that the IC phase results from a frustration of the lock-in spin-Peierls transition due to the competition of three energetically almost degenerate crystal structures and elastic coupling of the Ti chains via the bridging PO4 units. The phase transition into the IC phase is of second order, but the lock-in transition into the spin-Peierls distortion below 74.5 K is of weak first order in nature. [ABSTRACT FROM AUTHOR]

By performing density functional calculations, we investigate the origin of the Skyrmion state and ferroelectricity in Cu2OSeO3. We find that the Dzyaloshinskii-Moriya interactions between the two different kinds of Cu ions are extremely strong and induce the helical ground state and the Skyrmion state in the absence and presence of a magnetic field, respectively. On the basis of the general model for the spin-order induced polarization, we propose that the ferroelectric polarization of Cu2OSeO3 in the collinear ferrimagnetic state arises from an unusual mechanism, i.e., the single-spin-site contribution due to the spin-orbit coupling. [ABSTRACT FROM AUTHOR]

The nature of the magnetism brought about by Fe adatoms on the surface of the topological insulator Bi2Se3 was examined in terms of density functional calculations. The Fe adatoms exhibit strong easy-axis magnetic anisotropy in the dilute adsorption limit due to the topological surface states (TSS). The spin-exchange J between the Fe adatoms follows a Ruderman-Kittel-Kasuya-Yosida behavior with substantial anisotropy, and the Dzyaloshinskii-Moriya interaction between them is quite strong with ∣D/J∣ ≈ 0.3 under the mediation by the TSS and can be further raised to ∼0.6 by an external electric field. The apparent single-ion anisotropy of a Fe adatom is indispensable in determining the spin orientation [ABSTRACT FROM AUTHOR]

A novel general method of describing the spin-lattice interactions in magnetic solids is proposed in terms of first-principles calculations. The spin exchange and Dzyaloshinskii-Moriya interactions, as well as their derivatives with respect to atomic displacements, can be evaluated efficiently on the basis of density-functional calculations for four ordered spin states. By taking into consideration the spin-spin interactions, the phonons, and the coupling between them, we show that the ground-state structure of a representative spin-frustrated spinel, MgCr2O4, is tetragonally distorted, in agreement with experiments. However, our calculations find the lowest energy for the collinear spin ground state, in contrast to previously suggested noncollinear models. [ABSTRACT FROM AUTHOR]

We investigated the magnetic and structural properties of the quasi-one-dimensional 3d1 quantum chain system TiPO4 (J ∼ 965 K) by magnetic susceptibility, heat capacity, electron spin resonance, x-ray diffraction, and nuclear magnetic resonance (NMR) measurements, and by density functional theory (DFT) calculations. TiPO4 undergoes two magnetostructural phase transitions, one at 111 K and the other at 74 K. Below 74 K, NMR detects two different 31P signals and the magnetic susceptibility vanishes, while DFT calculations evidence a bond alternation of the Ti-Ti distances within each chain. Thus, the 74 K phase transition is a spin-Peierls transition which evolves from an incommensurate phase existing between 111 and 74 K. [ABSTRACT FROM AUTHOR]

Abstract: Using first principles density functional theory (DFT) calculations based on the full-potential linearized augmented plane wave method (LAPW), we investigated the electronic and magnetic structures for the ferromagnetic and antiferromagnetic states of La2MnNiO6 and analyzed the site-projected density of states and electronic dispersion curves. Our calculations show that the ground state of La2MnNiO6 is ferromagnetic insulating with the magnetization in agreement with Hund''s first rule and experimental findings. [Copyright &y& Elsevier]