110 research outputs found
Large bias-dependent magnetoresistance in all-oxide magnetic tunnel junctions with a ferroelectric barrier
All-oxide magnetic tunnel junctions (MTJs) incorporating functional materials
as insulating barriers have the potential of becoming the founding technology
for novel multi-functional devices. We investigate, by first-principles density
functional theory, the bias-dependent transport properties of an all-oxide
SrRuO3/BaTiO3/SrRuO3 MTJ. This incorporates a BaTiO3 barrier which can be found
either in a non-ferroic or in a ferroelectric state. In such an MTJ not only
can the tunneling magnetoresistance reach enormous values, but also, for
certain voltages, its sign can be changed by altering the barrier electric
state. These findings pave the way for a new generation of
electrically-controlled magnetic sensors.Comment: 4 pages, 5 figure
Coexistance of giant tunneling electroresistance and magnetoresistance in an all-oxide magnetic tunnel junction
We demonstrate with first-principles electron transport calculations that
large tunneling magnetoresistance (TMR) and tunneling electroresistance (TER)
effects can coexist in an all-oxide device. The TMR originates from the
symmetry-driven spin filtering provided by the insulating BaTiO3 barrier to the
electrons injected from SrRuO3. In contrast the TER is possible only when a
thin SrTiO3 layer is intercalated at one of the SrRuO3/BaTiO3 interfaces. As
the complex band-structure of SrTiO3 has the same symmetry than that of BaTiO3,
the inclusion of such an intercalated layer does not negatively alter the TMR
and in fact increases it. Crucially, the magnitude of the TER also scales with
the thickness of the SrTiO3 layer. The SrTiO3 thickness becomes then a single
control parameter for both the TMR and the TER effect. This protocol offers a
practical way to the fabrication of four-state memory cells
Topological surface states scattering in Antimony
In this work we study the topologically protected states of the Sb(111)
surface by using ab-initio transport theory. In the presence of a strong
surface perturbation we obtain standing-wave states resulting from the
superposition of spin-polarized surface states. By Fourier analysis, we
identify the underlying two dimensional scattering processes and the spin
texture. We find evidence of resonant transmission across surface barriers at
quantum well states energies and evaluate their lifetimes. Our results are in
excellent agreement with experimental findings. We also show that despite the
presence of a step edge along a different high symmetry direction, not yet
probed experimentally, the surface states exhibit unperturbed transmission
around the Fermi energy for states with near to normal incidence.Comment: Updated text, reference added, published versio
Electronic Transport Through EuO Spin Filter Tunnel Junctions
Epitaxial spin filter tunnel junctions based on the ferromagnetic
semiconductor europium monoxide, EuO, are investigated by means of density
functional theory. In particular, we focus on the spin transport properties of
Cu(100)/EuO(100)/Cu(100) junctions. The dependence of the transmission
coefficient and the current-voltage curves on the interface spacing and on the
EuO thickness is explained in terms of the EuO density of states and the
complex band structure. Furthermore we also discuss the relation between the
spin transport properties and the Cu-EuO interface geometry. The level
alignment of the junction is sensitively affected by the interface spacing,
since this determines the charge transfer between EuO and the Cu electrodes.
Our calculations indicate that EuO epitaxially grown on Cu can act as a perfect
spin filter, with a spin polarization of the current close to 100%, and with
both the Eu-5d conduction band and the Eu-4f valence band states contributing
to the coherent transport. For epitaxial EuO on Cu a symmetry filtering is
observed, with the \Delta_1 states dominating the transmission. This leads to a
transport gap larger than the fundamental EuO band gap. Importantly the high
spin polarization of the current is preserved up to large bias voltages
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