120 research outputs found
Perpendicular transport and magnetization processes in magnetic multilayers with strongly and weakly coupled magnetic layers
Within the framework of a two-band tight-binding model, we have performed
calculations of giant magnetoresistance, exchange coupling and thermoelectric
power (TEP) for a system consisting of three magnetic layers separated by two
non-magnetic spacers with the first two magnetic layers strongly
antiferromagnetically exchange-coupled. We have shown how does the GMR relate
with the corresponding regions of magnetic structure phase diagrams and
computed some relevant hysteresis loops, too. The GMR may take negative values
for specific layers thicknesses, and the TEP reveals quite pronounced
oscillations around a negative bias.Comment: 16 pages, 10 figures, submited to Journal of Magnetism and Magnetic
Material
Oscillatory Thickness Dependence of Magnetic Moments and interface-induced Changes of the Exchange Coupling in Co/Cu and Co-Ni/Cu Multilayers
We perform first-principles calculations for the three multilayer systems
(100)-Co_1/Cu_n, -NiCo_2Ni/Cu_n and -Co_4/Cu_n, and find from a comparison x of
the results for system 2 and 3 that amplitude and phase of the exchange
coupling are sensitive to the magnetic-slab/nonmagnetic-spacer interface.
Moreover, we observe that for the system 1 and 2 the averaged magnetic moment
of the magnetic slab oscillates with the spacer thickness similarly as the
exchange coupling.Comment: 5 pages (Latex, to be applied 2 times) + 2 figures (.ps-files
Spin transport in disordered single-wall carbon nanotubes contacted to ferromagnetic leads
Recent conductance measurements on multi-wall carbon nanotubes (CNTs) reveal
an effective behavior similar to disordered single-wall CNTs. This is due to
the fact that electric current flows essentially through the outermost shell
and is strongly influenced by inhomogeneous electrostatic potential coming from
the inner tubes. Here, we present theoretical studies of spin-dependent
transport through disorder-free double-wall CNTs as well as single-wall CNTs
with Anderson-type disorder. The CNTs are end-contacted to ferromagnetic
electrodes modelled as fcc (111) surfaces. Our results shed additional light on
the giant magnetoresistance effect in CNTs. Some reported results concern
realistically long CNTs, up to several hundred nanometers.Comment: 9 pages, 5 figures, presented at the European Conference PHYSICS OF
MAGNETISM 2005, Poznan, Polan
First principles studies of modulated Co/Cu superlattices with strongly and weakly exchange biased Co-monolayers
First-principles calculations have been performed in order to determine
effective exchange integrals between {\it strongly} and {\it weakly}
exchange-coupled Co monolayers in certain modulated periodic
-type superlattices with three non-equivalent Co planes, which
have not yet been studied hitherto. For we find that the two
non-equivalent exchange integrals have opposite signs, i.e.~the strong coupling
is antiferromagnetic and the weak coupling ferromagnetic, and differ for from each other by one order of magnitude. It is shown that the results
depend on the system as a whole and could not be obtained from separate parts.
Finally we suggest that ''spin valve'' systems of such kind should be
considered when trying to obtain good magneto-resistance together with low
switching-fields.Comment: LaTex, 9 pages, including two .eps-figure
Spin-polarized transport through carbon nanotubes
Carbon nanotubes (CNT) belong to the most promising new materials which can
in the near future revolutionize the conventional electronics. When sandwiched
between ferromagnetic electrodes, the CNT behaves like a spacer in conventional
spin-valves, leading quite often to a considerable giant magneto-resistance
effect (GMR). This paper is devoted to reviewing some topics related to
electron correlations in CNT. The main attention however is directed to the
following effects essential for electron transport through nanotubes: (i)
nanotube/electrode coupling and (ii) inter-tube interactions.It is shown that
these effects may account for some recent experimental reports on GMR,
including those on negative (inverse) GMR.Comment: 7 pages, 3 figure
CPP- Giant Magnetoresistance and Thermo-Electric Power of multilayers
Oscillations of magnetoresistance and thermo-electric power (TEP) vs. both
nonmagnetic spacer as well as ferromagnetic slab thicknesses are studied in the
current-perpendicular-to-plane (CPP) geometry, in terms of a single-band
tight-binding model. The spin-dependent conductance has been calculated from
the Kubo formula by means of a recursion Green's function technique, and the directly from the well-known Onsager relations.
In general, the observed oscillations may have either just one or two
periods. In the latter case the long period of oscillations, related to
spectacular beats, is apparently of non-RKKY type.
The relative TEP oscillations are strongly enhanced in comparison with those
of the giant magnetoresistance, have the same periods, but different phases and
a negative bias.Comment: Latex (4 pages); 2 figures included; to appear in Proc. of 'Physics
of Magn. 1996', Acta Physica Polonic
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