51 research outputs found
Spin-dependent thermoelectric effects in transport through a nanoscopic junction involving spin impurity
Conventional and spin-related thermoelectric effects in transport through a
magnetic tunnel junction with a large-spin impurity, such as a magnetic
molecule or atom, embedded into the corresponding barrier are studied
theoretically in the linear-response regime. The impurity is described by the
giant spin Hamiltonian, with both uniaxial and transverse magnetic anisotropy
taken into account. Owing to the presence of transverse component of magnetic
anisotropy, spin of a tunneling electron can be reversed during scattering on
the impurity, even in the low temperature regime. This reversal appears due to
exchange interaction of tunneling electrons with the magnetic impurity. We
calculate Seebeck and spin Seebeck coefficients, and analyze their dependence
on various parameters of the spin impurity and tunnel junction. In addition,
conventional and spin figures of merit, as well as the electronic contribution
to heat conductance are considered. We also show that pure spin current can be
driven by a spin bias applied to the junction with spin impurity, even if no
electron transfer between the electrodes can take place. The underlying
mechanism employs single-electrode tunneling processes (electrode-spin exchange
interaction) and the impurity as an intermediate reservoir of angular momentum.Comment: 24 pages with 7 figures, version as publishe
Effects of Transverse Magnetic Anisotropy on Current-Induced Spin Switching
Spin-polarized transport through bistable magnetic adatoms or single-molecule
magnets (SMMs), which exhibit both uniaxial and transverse magnetic anisotropy,
is considered theoretically. The main focus is on the impact of transverse
anisotropy on transport characteristics and the adatom's/SMM's spin. In
particular, we analyze the role of quantum tunneling of magnetization (QTM) in
the mechanism of the current-induced spin switching, and show that the QTM
phenomenon becomes revealed as resonant peaks in the average values of the
molecule's spin and in the charge current. These features appear at some
resonant fields and are observable when at least one of the electrodes is
ferromagnetic. We also show that the conductance generally depends on the
relative orientation of the average adatom's/SMM's spin and electrode's
magnetic moment. This spin-valve like magnetoresistance effect can be used to
control spin switching of the adatom's/SMM's spin.Comment: 5 pages, 3 figures (submitted
Effect of magnetic anisotropy on spin-dependent thermoelectric effects in nanoscopic systems
Conventional and spin-related thermoelectric effects in electronic transport
through a nanoscopic system exhibiting magnetic anisotropy with both
uniaxial and transverse components are studied theoretically in the linear
response regime. In particular, a magnetic tunnel junction with a large-spin
impurity either a magnetic atom or a magnetic molecule embedded in the
barrier is considered as an example. Owing to magnetic interaction with the
impurity, conduction electrons traversing the junction can scatter on the
impurity, which effectively can lead to angular momentum and energy exchange
between the electrons and the impurity. As we show, such processes have a
profound effect on the thermoelectric response of the system. Specifically, we
present a detailed analysis of charge, spin and thermal conductance, together
with the Seebeck and spin Seebeck coefficients (thermopowers). Since the
scattering mechanism also involves processes when electrons are inelastically
scattered back to the same electrode, one can expect the flow of spin and
energy also in the absence of charge transport through the junction. This, in
turn, results in a finite spin thermopower, and the magnetic anisotropy plays a
key role for this effect to occur.Comment: 23 pages with 16 figures; version as publishe
Spin Polarized Transport Through a Single-Molecule Magnet: Current-Induced Magnetic Switching
Magnetic switching of a single-molecule magnet (SMM) due to spin-polarized
current is investigated theoretically. The charge transfer between the
electrodes takes place via the lowest unoccupied molecular orbital (LUMO) of
the SMM. Generally, the double occupancy of the LUMO level, and a finite
on-site Coulomb repulsion, is taken into account. Owing to the exchange
interaction between electrons in the LUMO level and the SMM's spin, the latter
can be reversed. The perturbation approach (Fermi golden rule) is applied to
calculate current-voltage characteristics. The influence of Coulomb
interactions on the switching process is also analyzed.Comment: 5 pages with 4 EPS figures; version as accepted for publication in
Phys. Rev. B (more general model introduced
Negative tunnel magnetoresistance and differential conductance in transport through double quantum dots
Spin-dependent transport through two coupled single-level quantum dots weakly
connected to ferromagnetic leads with collinear magnetizations is considered
theoretically. Transport characteristics, including the current, linear and
nonlinear conductance, and tunnel magnetoresistance are calculated using the
real-time diagrammatic technique in the parallel, serial, and intermediate
geometries. The effects due to virtual tunneling processes between the two dots
via the leads, associated with off-diagonal coupling matrix elements, are also
considered. Negative differential conductance and negative tunnel
magnetoresistance have been found in the case of serial and intermediate
geometries, while no such behavior has been observed for double quantum dots
coupled in parallel. It is also shown that transport characteristics strongly
depend on the magnitude of the off-diagonal coupling matrix elements.Comment: 12 pages, 13 figure
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