157 research outputs found
Theory of Anomalous X-ray Scattering in Orbital Ordered Manganites
We study theoretically the anomalous X-ray scattering as a new probe to
observe the orbital orderings and excitations in perovskite manganites. The
scattering matrix is given by the virtual electronic excitations from Mn
level to unoccupied Mn level. We find that orbital dependence of the
Coulomb interaction between Mn and Mn electrons is essential to bring
about the anisotropy of the scattering factor near the K edge. The calculated
results in clusters explain the forbidden reflections observed in
and . A possibility of the observation of the
orbital waves by the X-ray scattering is discussed.Comment: 4 pages, 2 figure
Diluted magnetic semiconductors with narrow band gaps
We propose a method to realize diluted magnetic semiconductors (DMS) with p-
and n-type carriers by choosing host semiconductors with a narrow band gap. By
employing a combination of the density function theory and quantum Monte Carlo
simulation, we demonstrate such semiconductors using Mn-doped BaZn2As2, which
has a band gap of 0.2 eV. In addition, we found a new non-toxic DMS Mn-doped
BaZn2Sb2, of which the Curie temperature Tc is predicted to be higher than that
of Mn-doped BaZn2As2, the Tc of which was up to 230 K in the recent experiment.Comment: 18 pages, 12 figure
Magnetic power inverter: AC voltage generation from DC magnetic fields
We propose a method that allows power conversion from DC magnetic fields to
AC electric voltages using domain wall (DW) motion in ferromagnetic nanowires.
The device concept relies on spinmotive force, voltage generation due to
magnetization dynamics. Sinusoidal modulation of the nanowire width introduces
a periodic potential for a DW the gradient of which exerts variable pressure on
the traveling DW. This results in time variation of the DW precession frequency
and the associated voltage. Using a one-dimensional model we show that the
frequency and amplitude of the AC outputs can be tuned by the DC magnetic
fields and wire-design
Orbital Ordering and Resonant X-ray Scattering in Layered Manganites
In layered manganites with orbital and charge orderings, the degeneracy of
the Mn orbitals as well as the ones is lifted by the effects of the
bands and the local Coulomb interactions. We formulate the atomic
scattering factor for the resonant x-ray scattering in the memory function
method by taking into account these effects on an equal footing. It is shown
that the polarization dependences of the scattering intensities at the orbital
and charge superlattice reflections observed in LaSrMnO are
caused by the local and itinerant characters of electrons, respectively.
We examine the type of the orbital ordered state.Comment: 4 pages, 3 figure
Theory of Orbital Excitation and Resonant Inelastic X-ray Scattering in Manganites
We study theoretically the collective orbital excitation named orbital wave
in the orbital ordered manganites.The dispersion relation of the orbital wave
is affected by the static spin structure through the coupling between spin and
orbital degrees of freedom. As a probe to detect the dispersion relation, we
propose two possible methods by utilizing resonant inelastic x-ray scattering.
The transition probability of the orbital wave scattering is formulated, and
the momentum and polarization dependences of the structure factor are
calculated in several types of the orbital and spin structures. The elastic
x-ray scattering in the L-edge case to observe the orbital ordering is also
discussed.Comment: 11 pages, 10 figure
Theory of spin hydrodynamic generation
Spin-current generation by fluid motion is theoretically investigated. Based
on quantum kinetic theory, the spin-diffusion equation coupled with fluid
vorticity is derived. We show that spin currents are generated by the vorticity
gradient in both laminar and turbulent flows and that the generated spin
currents can be detected by the inverse spin Hall voltage measurements, which
are predicted to be proportional to the flow velocity in a laminar flow. In
contrast, the voltage in a turbulent flow is proportional to the square of the
flow velocity. This study will pave the way to fluid spintronics.Comment: 5 pages, 3 figure
Spinmotive force with static and uniform magnetization induced by a time-varying electric field
A new spinmotive force is predicted in ferromagnets with spin-orbit coupling.
By extending the theory of spinmotive force, we show that a time-varying
electric field can induce a spinmotive force with static and uniform
magnetization. This spinmotive has two advantages; it can be detected free from
the inductive voltage owing to the absence of dynamical magnetization and it
can be tuned by electric fields. To observe the effect, we propose two
experimental setups: electric voltage measurement in a single ferromagnet and
spin injection from a ferromagnet into an attached nonmagnetic conductor
Renormalization of spin-rotation coupling
We predict the enhancement of the spin-rotation coupling due to the interband
mixing. The Bloch wavefunctions in the presence of mechanical rotation are
constructed with the generalized crystal momentum which includes a gauge
potential arising from the rotation. Using the eight- band Kane model, the
renormalized spin-rotation coupling is explicitly obtained. As a result of the
renormalization, the rotational Doppler shift in electron spin resonance and
the mechanical torque on an electron spin will be strongly modulated.Comment: 8 page
Crossed Andreev Reflection in Structures Consisting of a Superconductor with Ferromagnetic Leads
A theory of crossed Andreev reflection in structures consisting of a
superconductor with two ferromagnetic leads is presented. The electric current
due to the crossed Andreev reflection strongly depends on the relative
orientation of the magnetization of two ferromagnetic leads. It is shown that
the dependence of the electric current and the magnetoresistance on the
distance between two ferromagnetic leads is understood by considering the
interference between the wave functions in ferromagnets. The current and the
magnetoresistance are calculated as functions of the exchange field and the
height of the interfacial barriers.Comment: 9 pages, 9 figure
Systematic Study of Magnetic Interactions in Insulating Cuprates
The magnetic interactions in one-dimensional, two-dimensional (2D) and ladder
cuprates are evaluated systematically by using small Cu-O clusters. We find
that the superexchange interaction J between nearest neighbor Cu spins strongly
depends on Cu-O structure through the Madelung potential, and in 2D and ladder
cuprates there is a four-spin interaction Jcyc, with magnitude of 10% of J. We
show that Jcyc has a strong influence on the magnetic excitation in the
high-energy region of 2D cuprates.Comment: 2 pages, 1 figure, with minor corrections, M2S-HTSC-VI conference
proceeding
- β¦