85 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
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
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
Theoretical studies of spin-dependent electronic transport in ferromagnetically contacted graphene flakes
Based on a tight-binding model and a recursive Green's function technique,
spin-depentent ballistic transport through tinny graphene sheets (flakes) is
studied. The main interest is focussed on: electrical conductivity, giant
magnetoresistance (GMR) and shot noise. It is shown that when graphene flakes
are sandwiched between two ferromagnetic electrodes, the resulting GMR
coefficient may be quite significant. This statement holds true both for zigzag
and armchair chiralities, as well as for different aspect (width/length)
ratios. Remarkably, in absolute values the GMR of the armchair-edge graphene
flakes is systematically greater than that corresponding to the zigzag-edge
graphene flakes. This finding is attributed to the different degree of
conduction channel mixing for the two chiralities in question. It is also shown
that for big aspect ratio flakes, 3-dimensional end-contacted leads, very much
like invasive contacts, result in non-universal behavior of both conductivity
and Fano factor.Comment: to appear in PR
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