1,126 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
Magnetic Phase Control in Monolayer Films by Substrate Tuning
We propose to tailor exchange interactions in magnetic monolayer films by
tuning the adjacent non-magnetic substrate. As an example, we demonstrate a
ferromagnetic-antiferromagnetic phase transition for one monolayer Fe on a
Ta(x)W(1-x)(001) surface as a function of the Ta concentration. At the critical
Ta concentration, the nearest-neighbor exchange interaction is small and the
magnetic phase space is dramatically broadened. Complex magnetic order such as
spin-spirals, multiple-Q, or even disordered local moment states can occur,
offering the possibility to store information in terms of ferromagnetic dots in
an otherwise zero-magnetization state matrix.Comment: after minor changes, 5 pages, 5 figures, revtex
Magnetism of mixed quaternary Heusler alloys: (Ni,T)MnSn (T=Cu,Pd) as a case study
The electronic properties, exchange interactions, finite-temperature
magnetism, and transport properties of random quaternary Heusler NiMnSn
alloys doped with Cu- and Pd-atoms are studied theoretically by means of {\it
ab initio} calculations over the entire range of dopant concentrations. While
the magnetic moments are only weakly dependent on the alloy composition, the
Curie temperatures exhibit strongly non-linear behavior with respect to
Cu-doping in contrast with an almost linear concentration dependence in the
case of Pd-doping. The present parameter-free theory agrees qualitatively and
also reasonably well quantitatively with the available experimental results. An
analysis of exchange interactions is provided for a deeper understanding of the
problem. The dopant atoms perturb electronic structure close to the Fermi
energy only weakly and the residual resistivity thus obeys a simple Nordheim
rule. The dominating contribution to the temperature-dependent resistivity is
due to thermodynamical fluctuations originating from the spin-disorder, which,
according to our calculations, can be described successfully via the disordered
local moments model. Results based on this model agree fairly well with the
measured values of spin-disorder induced resistivity.Comment: 13 pages, 13 figure
Quantum graph as a quantum spectral filter
We study the transmission of a quantum particle along a straight
input--output line to which a graph is attached at a point. In the
point of contact we impose a singularity represented by a certain properly
chosen scale-invariant coupling with a coupling parameter . We show
that the probability of transmission along the line as a function of the
particle energy tends to the indicator function of the energy spectrum of
as . This effect can be used for a spectral analysis
of the given graph . Its applications include a control of a
transmission along the line and spectral filtering. The result is illustrated
with an example where is a loop exposed to a magnetic field. Two more
quantum devices are designed using other special scale-invariant vertex
couplings. They can serve as a band-stop filter and as a spectral separator,
respectively.Comment: 15 pages, 8 figures. Copyright (2013) American Institute of Physics.
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