16 research outputs found
Substrate-induced antiferromagnetism of an Fe monolayer on the Ir(001) surface
We present detailed ab initio study of structural and magnetic stability of a
Fe-monolayer on the fcc(001) surface of iridium. The Fe-monolayer has a strong
tendency to order antiferromagnetically for the true relaxed geometry. On the
contrary an unrelaxed Fe/Ir(001) sample has a ferromagnetic ground state. The
antiferromagnetism is thus stabilized by the decreased Fe-Ir layer spacing in
striking contrast to the recently experimentally observed antiferromagnetism of
the Fe/W(001) system which exists also for an ideal bulk-truncated, unrelaxed
geometry. The calculated layer relaxations for Fe/Ir(001) agree reasonably well
with recent experimental LEED data. The present study centers around the
evaluation of pair exchange interactions between Fe-atoms in the Fe-overlayer
as a function of the Fe/Ir interlayer distance which allows for a detailed
understanding of the antiferromagnetism of a Fe/Ir(001) overlayer. Furthermore,
our calculations indicate that the nature of the true ground state could be
more complex and display a spin spiral-like rather than a
c(2x2)-antiferromagnetic order. Finally, the magnetic stability of the Fe
monolayer on the Ir(001) surface is compared to the closely related Fe/Rh(001)
system.Comment: 8 pages, 4 figure
Magnetism without magnetic impurities in oxides ZrO2 and TiO2
We perform a theoretical study of the magnetism induced in transition metal
dioxides ZrO2 and TiO2 by substitution of the cation by a vacancy or an
impurity from the groups 1A or 2A of the periodic table, where the impurity is
either K or Ca. In the present study both supercell and embedded cluster
methods are used. It is demonstrated that the vacancy and the K-impurity leads
to a robust induced magnetic moment on the surrounding O-atoms for both the
cubic ZrO2 and rutile TiO2 host crystals. On the other hand it is shown that
Ca-impurity leads to a non magnetic state. The native O-vacancy does not induce
a magnetic moment in the host dioxide crystal.Comment: 7 pages, 5 figures, submitte
Temperature-dependent resistivity and anomalous Hall effect in NiMnSb from first principles
© 2019 American Physical Society. We present implementation of the alloy analogy model within fully relativistic density-functional theory with the coherent potential approximation for a treatment of nonzero temperatures. We calculate contributions of phonons and magnetic and chemical disorder to the temperature-dependent resistivity, anomalous Hall conductivity (AHC), and spin-resolved conductivity in ferromagnetic half-Heusler NiMnSb. Our electrical transport calculations with combined scattering effects agree well with experimental literature for Ni-rich NiMnSb with 1-2% Ni impurities on Mn sublattice. The calculated AHC is dominated by the Fermi surface term in the Kubo-Bastin formula. Moreover, the AHC as a function of longitudinal conductivity consists of two linear parts in the Ni-rich alloy, while it is nonmonotonic for Mn impurities. We obtain the spin polarization of the electrical current P>90% at room temperature and we show that P may be tuned by chemical composition. The presented results demonstrate the applicability of an efficient first-principles scheme to calculate temperature dependence of linear transport coefficients in multisublattice bulk magnetic alloys
Electronic structure of disordered alloys, surfaces and interfaces
At present, there is an increasing interest in the prediction of properties of classical and new materials such as substitutional alloys, their surfaces, and metallic or semiconductor multilayers. A detailed understanding based on a thus of the utmost importance for fu microscopic, parameter-free approach is ture developments in solid state physics and materials science. The interrela tion between electronic and structural properties at surfaces plays a key role for a microscopic understanding of phenomena as diverse as catalysis, corrosion, chemisorption and crystal growth. Remarkable progress has been made in the past 10-15 years in the understand ing of behavior of ideal crystals and their surfaces by relating their properties to the underlying electronic structure as determined from the first principles. Similar studies of complex systems like imperfect surfaces, interfaces, and mul tilayered structures seem to be accessible by now. Conventional band-structure methods, however, are of limited use because they require an excessive number of atoms per elementary cell, and are not able to account fully for e.g. substitu tional disorder and the true semiinfinite geometry of surfaces. Such problems can be solved more appropriately by Green function techniques and multiple scattering formalism