739 research outputs found
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
Fluidic low speed wind sensor research study Final report, Oct. 1968 - Oct. 1969
Cross flow and parallel flow concepts of fluidic wind speed sensor
Correlated Doping in Semiconductors: The Role of Donors in III-V Diluted Magnetic Semiconductors
We investigate the compositional dependence of the total energy of the mixed
crystals (Ga,Mn)As co-doped with As, Sn, and Zn. Using the ab initio LMTO-CPA
method we find a correlation between the incorporation of acceptors (Mn, Zn)
and donors (Sn, antisite As). In particular, the formation energy of As_Ga is
reduced by approx. 0.1 eV in the presence of Mn, and vice versa. This leads to
the self-compensating behavior of (Ga,Mn)As.Comment: 8 pages, 2 figures, presented at the XXXI Int. School of
Semiconducting Compounds, Jaszowiec 2002, Polan
Thermopower of a superconducting single-electron transistor
We present a linear-response theory for the thermopower of a single-electron
transistor consisting of a superconducting island weakly coupled to two
normal-conducting leads (NSN SET). The thermopower shows oscillations with the
same periodicity as the conductance and is rather sensitive to the size of the
superconducting gap. In particular, the previously studied sawtooth-like shape
of the thermopower for a normal-conducting single-electron device is
qualitatively changed even for small gap energies.Comment: 9 pages, 3 figure
Interface resistance of disordered magnetic multilayers
We study the effect of interface disorder on the spin-dependent interface
resistances of Co/Cu, Fe/Cr and Au/Ag multilayers using a newly developed
method for calculating transmission matrices from first-principles. The
efficient implementation using tight-binding linear-muffin-tin orbitals allows
us to model interface disorder using large lateral supercells whereby specular
and diffuse scattering are treated on an equal footing. Without introducing any
free parameters, quantitative agreement with experiment is obtained. We predict
that disorder {\it reduces} the majority-spin interface resistance of
Fe/Cr(100) multilayers by a factor 3.Comment: 5 pages, 2 figures, submitted to PR
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