Václav Drchal

Electronic structure of disordered alloys, surfaces and interfaces

Preface. 1. Introduction. 2. Linear Muffin-Tin Orbital (LMTO) Method. 3. Green Function Method. 4. Coherent Potential Approximation (CPA). 5. Selfconsistency within Atomic Sphere Approximation. 6. Relativistic Theory. 7. Bulk Systems, Overlayers and Surfaces. 8. Magnetic Properties. 9. Effective Interatomic Interactions in Alloys. 10. Numerical Implementation. Index.

Magnetism without magnetic impurities in ZrO2 oxide

We present an ab initio study of the magnetism induced in ZrO2 dioxide by substitution of the cation by an impurity from the groups 1A or 2A of the Periodic Table (K and Ca). It is demonstrated that the K impurity leads to a robust induced magnetic moment on the surrounding O atoms in the cubic ZrO2 host whilst Ca impurity leads to a nonmagnetic groundstate. The estimated Curie temperature is above room temperature.

Electronic Structure and Nonmagnetic Character of Delta-Pu-Am Alloys

The around-mean-field LSDA+U correlated band theory is applied to investigate the electronic and magnetic structure of fcc-Pu-Am alloys. Despite a lattice expansion caused by the Am atoms, neither ...

Multiplet effects in the electronic structure of δ-Pu, Am and their compounds

We propose a straightforward and efficient procedure to perform dynamical mean-field (DMFT) calculations on the top of the static mean-field LDA+U approximation. Starting from self-consistent LDA+U ground state we included multiplet transitions using the Hubbard-I approximation, which yields a very good agreement with experimental photoelectron spectra of δ-Pu, Am, and their selected compounds.

Residual resistivity of diluted III-V magnetic semiconductors

The electronic structure and residual resistivity of diluted (Ga, Mn)As magnetic semiconductors are calculated from first principles using the linear muffin-tin orbital method, the coherent potential approximation, and the Kubo-Greenwood linear response theory. Particular attention is paid to the role of native compensating defects such as As antisites and Mn interstitials as well as to different magnetic configurations of the local Mn moments. The order of magnitude of the calculated resistivities compares reasonably well with available experimental data. The concentration variations of the resistivity reflect two basic mechanisms, namely the strength of the impurity scattering and the number of carriers. In agreement with a recent experiment, the calculated resistivities are strongly correlated with the alloy Curie temperatures evaluated in terms of a classical Heisenberg Hamiltonian.

Interlayer exchange coupling through ordered and disordered alloy spacers

The interlayer exchange coupling between ferromagnetic films separated by a disordered or ordered alloy spacer layer is considered theoretically. This is illustrated by first-principles calculations for fcc Co(OO1) films separated by disordered CU,_,N~,~, CU,-~Z~~~ and CU,-~~AU,, and by ordered CuAu alloys. For the CuAu spacer, the case of partial ordering in the alloy is also considered.

Green Function Method

In this chapter, we derive a general expression for the Green function corresponding to a one-electron problem solved within the atomic sphere approximation. On the basis of this Green function formalism, methods for an efficient treatment of systems with two-dimensional translational symmetry are described: the tight-binding linear muffin-tin orbital method, a technique of principal layers and surface Green functions, and concepts in order to calculate important physical observables.

Pressure effect on magnetic moments in ordered Ni3Mn and disordered Ni100−x Mn x alloys: ab initio calculation and experiment

We have revealed a substantial difference in the pressure behavior of magnetization of the ordered Ni3Mn and the disordered Ni75Mn25 and Ni80Mn20 alloys in the pressure range up to 1.2 GPa. To explain in detail the peculiarities of magnetic properties of the Ni-rich NiMn alloys, the reference electronic structure of the alloys was calculated using the tight-binding linear muffin-tin orbital approach. The effect of disorder was described by the coherent potential approximation. The theoretical ab initio calculations (with changes of the lattice parameters up to 1%) elucidated the pressure stability of the magnetic Mn moments and revealed that the very pronounced decrease in the magnetization of the disordered alloys under pressure is caused by the relatively small change in portion of the Mn moments with parallel and anti-parallel orientation with respect to the total moment. The quantitative agreement with experiment has been reached for the pressure parameters dln M/dP.

Oscillatory behavior of interface exchange coupling caused by finite caps of variable thickness

The effect of non-magnetic cap-layers on the periods and the amplitudes of the oscillations of interlayer exchange coupling (IEC) is studied theoretically using an ab initio spin-polarized surface Green function technique within a tight-binding linear muffin-tin orbital method and the Lloyd formulation of the IEC Applications are made to the free-electron like model as well as to Co/Cu/Co(O 0 1) trilayers with a cap interfacing vacuum through the dipole barrier. The results are analyzed in terms of a discrete two-dimensional Fourier transformation which confirms a pronounced oscillatory behavior of the IEC with respect to the thickness of the cap- and the spacer-layers. The results are in agreement with available experimental data as well as with predictions of the electron confinement model of the IEC. Copyright 0 1998 Elsevier Science B.V. The oscillatory interlayer exchange coupling (IEC) between magnetic layers separated by a non-magnetic spacer hlas recently attracted considerable attention. The physical origin of such oscillations is attributed to quantum interferences due to spin-dependent confinement of electrons in the spacer [ 141. An important conclusion, namely tihat the periods of the oscillations with respect to the spacer thickness are determined by the spacer Fermi surface, bas been confirmed by numerous experiments. Recently increasing interest was devoted to the study of the influence of the cap [5-71 on the IEC, and first model dheories have appeared based on simple free-electron-like models [6-91. These theories predict a novel oscillatory behavior of the IEC with respect to the thickness of the cap, which is attributed to electron confinement in the non-magnetic cap due to the vacuum barrier 191. The peiriods of these oscillations are related to the Fermi-surface of the cap material. Experimental observations of the oscillations of the IEC with respect to the cap thickness in a

Influence of oxygen and hydrogen adsorption on the magnetic structure of an ultrathin iron film on an Ir(001) surface

We present a detailed ab initio study of the electronic structure and magnetic order of an Fe monolayer on the Ir(001) surface covered by adsorbed oxygen and hydrogen. The results are compared to the clean Fe/Ir(001) system, where recent intensive studies indicated a strong tendency towards an antiferromagnetic order and complex magnetic structures. The adsorption of an oxygen overlayer significantly increases interlayer distance between the Fe layer and the Ir substrate, while the effect of hydrogen is much weaker. We show that the adsorption of oxygen (and also of hydrogen) leads to a p(2