L. M. Sandratskii

Band theory for electronic and magnetic properties of

We report results of calculations that explain in the itinerant-electron picture magnetic and electronic properties of haematite, . For this we use the local approximation to spin-density functional theory and the ASW method incorporating spin - orbit coupling and noncollinear moment arrangements. The insulating character of the compound is obtained correctly and features in the density of states connected with Fe - O hybridization correlate well with experimental features seen in direct and inverse photoemission intensities. The total energy correctly predicts the experimentally observed magnetic order of the ground state, and, using total energies of different magnetic configurations, we can give a rough estimate of the Neel temperature. We also obtain a state showing weak ferromagnetism. The rate of change is calculated for the decrease of the insulating gap when an external magnetic field is applied.

Electronic and magnetic states of γ-Fe

Abstract The electronic and magnetic structure of fcc (γ-)Fe is determined using the local spin-density functional approximation and the ASW method to solve the band-structure problem self-consistently. The calculations reveal that the detailed nature of the ground state of γ-Fe depends sensitively on the volume but quite unambigously consists of a spiral magnetic structure that is incommensurate with the lattice, in agreement with recent neutron-diffraction experiments. We give, in some detail, the theory necessary to implement the calculations. The noncollinear spin arrangement is described using for the spiral vector q a wide range of values that continuously cover ferromagnetic and antiferromagnetic configurations. The stability of the structure having minimum total energy is related to band-structure features and we emphasize the occurence of multiple magnetic states, which we study using a “constrained-moments” method.

The Fermi surface of

The de Haas - van Alphen spectrum of is calculated and compared with the experimental spectrum for continuously varying directions of the magnetic field. The local density approximation to spin-density functional theory is used for the self-consistent calculations treating the U 5f electrons as itinerant and including spin - orbit coupling. The amount of f angular momentum character is obtained and exhibited graphically for each sheet of the Fermi surface. The band-decomposed spin susceptibility, , is calculated for the states at the Fermi surface and the anisotropy of is discussed.

Local magnetic moments of conduction electrons in gadolinium

Using the local-density-functional approximation to calculate self-consistently the spin-resolved density of states (DOS), we obtain qualitative information on the stability of the induced magnetic moments of conduction electrons in h.c.p. Gd with respect to the disordering of the spatially localized 4f moments. We show that the resulting changes in the DOS cannot be interpreted in terms of an exchange splitting of the conduction bands, but must be seen as an effect of spin-hybridization. We argue that the induced moments of conduction electrons are rather stable and do not disappear even above the Curie temperature. We reinterpret important features of recent photoemission experiments on Gd.

Noncollinear magnetic order and electronic properties of U2Pd2Sn and U3P4

Abstract We report results of calculations that explain in the itinerant electron picture the noncollinear magnetic structure observed in the two very different compounds U 2 Pd 2 Sn and U 3 P 4 . We use the local approximation to spin-density functional theory and the ASW method incorporating spin-orbit coupling (SOC), noncollinear moment arrangements and an effective orbital field responsible for Hunds second rule. We show how the relativistic effect of SOC and the particular symmetry properties of the compounds cooperate and lead to noncollinear magnetic structures, in the case of U 2 Pd 2 Sn to an antiferromagnetic and in the case of U 3 P 4 to a ferromagnetic structure, the latter possessing a weak antiferromagnetic component.

Theory for itinerant electrons in noncollinear and incommensurate structured magnets (invited)

Itinerant‐electron systems are described that can form a variety of magnetic‐moment arrangements. These are dealt with quantitatively by using energy‐band theory and the local density‐functional approximation; the theoretical and computational basis is briefly reviewed and results are presented for quite general collinear and noncollinear moment arrangements and states having incommensurate helical order characterized by a wave vector q. Some examples presented here are Fe3Pt‐Invar, fcc‐iron precipitates, and tetragonal iron. Furthermore, finite‐temperature effects become tractable; the magnetovolume effect in Fe3Pt‐Invar serves as an example. Finally, the problem of biquadratic exchange in Fe‐Cr multilayers will be discussed briefly.

Noncollinear spiral magnetic order in itinerant-electron magnets

Abstract We use the local spin-density functional approximation together with the ASW-method to solve the band-structure problem self-consistently for noncollinear, incommensurate spiral magnetic structures. These occur e.g. in γ-Fe according to recent neutron-diffraction experiments by Tsunoda. Our calculated total energies identify possible spiral ground states for γ-Fe and reveal certain band-structure features responsible. Another case treated is YMn 2 which possesses an antiferromagnetic ground state modulated by a long-period spiral. Our calculations correctly identify the latter but predict an antiferromagnetic order that differs from that suggested by Ballou et al. to explain neutron-diffraction data.

Electronic and magnetic properties of UPdSn: the itinerant 5f electrons approach

Density functional theory, modified to include spin - orbit coupling and an effective orbital field to simulate Hunds second rule, is applied to investigate the magnetic structure and electronic properties of the compound UPdSn. Our theoretical results are in overall good agreement with experiment. Thus both theory and experiment find the magnetic structure of UPdSn to be noncollinear, the calculated magnetic U-moments being in very good agreement with the measurements. Also, the calculated density of states is found to simulate closely the photoemission spectrum and the very low experimental value of for the specific heat is reproduced reasonably well by the calculated value of . Furthermore, the interconnection of the magnetic structure with the crystal structure is investigated. Here theory and experiment agree concerning the planar noncollinear antiferromagnetic configuration in the orthorhombic crystal structure and for the monoclinically distorted lattice we obtain deviations of the magnetic moments from the plane which, although qualitatively in agreement with the experimentally observed deviations, are smaller than the latter. We carry out a symmetry analysis and show that UPdSn belongs to the class of systems possessing a magnetic structure, the noncollinearity of which is predetermined by symmetry. Conclusions are drawn about the itinerant character of the U 5f electrons.

Spin-density functional theory of the magnetism of UT2Si2 compounds

Abstract The electronic structure of UT2Si2, where T = Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Os, is determined by means of self-consistent density-functional calculations treating the U 5f states as band states. A pronounced trend in the hybridization strength is exposed and is deduced to give rise to the different magnetic properties of the compounds. In agreement with experiment, the non-monotonic behavior in the subseries containing 3d elements is reproduced. The underlying physics of this fact is explained. Furthermore, special features of the heavy-fermion system URu2Si2 are discussed.

Symmetry properties of intra-atomic spin and angular momentum densities: application to

We consider the formation of the atomic spin and orbital moments in the framework of the local spin-density functional approximation by examining and exhibiting the symmetry properties of the intra-atomic spin and angular momentum densities, focusing on general principles, and elaborating by means of the realistic example of which is a noncollinear ferromagnet. We expose the role of the symmetry properties in determining the intra-atomic noncollinearity of the spin and orbital moments, which we connect with the inter-atomic configurations of the atomic moments.