38 research outputs found
Impact of tunnel barrier strength on magnetoresistance in carbon nanotubes
We investigate magnetoresistance in spin valves involving CoPd-contacted
carbon nanotubes. Both temperature and bias voltage dependence clearly indicate
tunneling magnetoresistance as the origin. We show that this effect is
significantly affected by the tunnel barrier strength, which appears to be one
reason for the variation between devices previously detected in similar
structures. Modeling the data by means of the scattering matrix approach, we
find a non-trivial dependence of the magnetoresistance on the barrier strength.
Furthermore, analysis of the spin precession observed in a nonlocal Hanle
measurement yields a spin lifetime of ns, a value comparable
with those found in silicon- or graphene-based spin valve devices.Comment: 10 pages, 5 figures, 1 tabl
Spintronic magnetic anisotropy
An attractive feature of magnetic adatoms and molecules for nanoscale
applications is their superparamagnetism, the preferred alignment of their spin
along an easy axis preventing undesired spin reversal. The underlying magnetic
anisotropy barrier --a quadrupolar energy splitting-- is internally generated
by spin-orbit interaction and can nowadays be probed by electronic transport.
Here we predict that in a much broader class of quantum-dot systems with spin
larger than one-half, superparamagnetism may arise without spin-orbit
interaction: by attaching ferromagnets a spintronic exchange field of
quadrupolar nature is generated locally. It can be observed in conductance
measurements and surprisingly leads to enhanced spin filtering even in a state
with zero average spin. Analogously to the spintronic dipolar exchange field,
responsible for a local spin torque, the effect is susceptible to electric
control and increases with tunnel coupling as well as with spin polarization.Comment: 6 pages with 4 figures + 26 pages of Supplementary Informatio
Probing Transverse Magnetic Anisotropy by Electronic Transport through a Single-Molecule Magnet
By means of electronic transport, we study the transverse magnetic anisotropy
of an individual Fe single-molecule magnet (SMM) embedded in a
three-terminal junction. In particular, we determine in situ the transverse
anisotropy of the molecule from the pronounced intensity modulations of the
linear conductance, which are observed as a function of applied magnetic field.
The proposed technique works at temperatures exceeding the energy scale of the
tunnel splittings of the SMM. We deduce that the transverse anisotropy for a
single Fe molecule captured in a junction is substantially larger than the
bulk value.Comment: 18 pages with 16 figures; version as publishe
Quantum Tunneling of Magnetization in Single Molecular Magnets Coupled to Ferromagnetic Reservoirs
The role of spin polarized reservoirs in quantum tunneling of magnetization
and relaxation processes in a single molecular magnet (SMM) is investigated
theoretically. The SMM is exchange-coupled to the reservoirs and also subjected
to a magnetic field varying in time, which enables the quantum tunneling of
magnetization (QTM). The spin relaxation times are calculated from the Fermi
golden rule. The exchange interaction with tunneling electrons is shown to
affect the spin reversal due to QTM. Furthermore, it is shown that the
switching is associated with transfer of a certain charge between the leads.Comment: 5 pages, 3 EPS figures, final version as publishe
Charge transport through single molecules, quantum dots, and quantum wires
We review recent progresses in the theoretical description of correlation and
quantum fluctuation phenomena in charge transport through single molecules,
quantum dots, and quantum wires. A variety of physical phenomena is addressed,
relating to co-tunneling, pair-tunneling, adiabatic quantum pumping, charge and
spin fluctuations, and inhomogeneous Luttinger liquids. We review theoretical
many-body methods to treat correlation effects, quantum fluctuations,
nonequilibrium physics, and the time evolution into the stationary state of
complex nanoelectronic systems.Comment: 48 pages, 14 figures, Topical Review for Nanotechnolog
Spin-Atomic Vibration Interaction and Spin-Flip Hamiltonian of a Single Atomic Spin in a Crystal Field
We derive the spin-atomic vibration interaction and the
spin-flip Hamiltonian of a single atomic spin in a crystal field.
We here apply the perturbation theory to a model with the spin-orbit
interaction and the kinetic and potential energies of electrons. The model also
takes into account the difference in vibration displacement between an
effective nucleus and electrons, \Delta {{\boldmath r}}. Examining the
coefficients of and , we first show that
appears for \Delta {{\boldmath r}}0, while is present
independently of \Delta {{\boldmath r}}. As an application, we next obtain
and of an Fe ion in a crystal field of tetragonal
symmetry. It is found that the magnitudes of the coefficients of
can be larger than those of the conventional spin-phonon interaction depending
on vibration frequency. In addition, transition probabilities per unit time due
to and are investigated for the Fe ion with an
anisotropy energy of , where is an anisotropy constant and
is the component of a spin operator.Comment: 55 pages, 17 figures, to be published in J. Phys. Soc. Jpn. 79 (2010)
No. 11, typos correcte