389 research outputs found
Theory of Current-Driven Domain Wall Motion: A Poorman's Approach
A self-contained theory of the domain wall dynamics in ferromagnets under
finite electric current is presented.
The current is shown to have two effects; one is momentum transfer, which is
proportional to the charge current and wall resistivity (\rhow), and the
other is spin transfer, proportional to spin current.
For thick walls, as in metallic wires, the latter dominates and the threshold
current for wall motion is determined by the hard-axis magnetic anisotropy,
except for the case of very strong pinning.
For thin walls, as in nanocontacts and magnetic semiconductors, the
momentum-transfer effect dominates, and the threshold current is proportional
to \Vz/\rhow, \Vz being the pinning potential
Effect of Spin Current on Uniform Ferromagnetism: Domain Nucleation
Large spin current applied to a uniform ferromagnet leads to a spin-wave
instability as pointed out recently.
In this paper, it is shown that such spin-wave instability is absent in a
state containing a domain wall, which indicates that nucleation of magnetic
domains occurs above a certain critical spin current.
This scenario is supported also by an explicit energy comparison of the two
states under spin current.Comment: 4 pages, 1 figure, REVTeX, rivised version, to appear in Physical
Review Letter
Microscopic Calculation of Spin Torques and Forces
Spin torques, that is, effects of conduction electrons on magnetization
dynamics, are calculated microscopically in the first order in spatial gradient
and time derivative of magnetization. Special attention is paid to the
so-called \beta-term and the Gilbert damping, \alpha, in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
impurities. Two types of forces that the electric/spin current exerts on
magnetization are identified based on a general formula relating the force to
the torque.Comment: Proceedings of ICM2006 (Kyoto), to appear in J. Mag. Mag. Ma
Electronic pressure on ferromagnetic domain wall
The scattering of the eletron by a domain wall in a nano-wire is studied
perturbatively to the lowest order. The correction to the thermodaynamic
potential of the electron system due to the scattering is calculated from the
phase shift. The wall profile is determined by taking account of this
correction, and the result indicates that the wall in a ferromagnet with small
exchange coupling can be squeezed to be very thin to lower the electron energy
On Aharonov-Bohm oscillation in a ferromagnetic ring
Aharonov-Bohm effect in a ferromagnetic thin ring in diffusive regime is
theoretically studied by calculating the Cooperon and Diffuson. In addition to
the spin-orbit interaction, we include the spin-wave excitation and the spin
splitting, which are expected to be dominant sources of dephasing in
ferromagnets at low temperatures. The spin splitting turns out to kill the
spin-flip channel of Cooperon but leaves the spin-conserving channel untouched.
For the experimental confirmation of interference effect (described by
Cooperons) such as weak localization and Aharonov-Bohm oscillation with period
, we need to suppress the dominant dephasing by orbital motion. To do
this we propose experiments on a thin film or thin ring with magnetization and
external field perpendicular to the film, in which case the effective field
inside the sample is equal to the external field (magnetization does not add
up). The field is first applied strong enough to saturate the magnetization and
then carrying out the measurement down to zero field keeping the magnetization
nearly saturated, in order to avoid domain formations (negative fields may also
be investigated if the coercive field is large enough)
Domain Wall Resistance based on Landauer's Formula
The scattering of the electron by a domain wall in a nano-wire is calculated
perturbatively to the lowest order. The resistance is calculated by use of
Landauer's formula. The result is shown to agree with the result of the linear
response theory if the equilibrium is assumed in the four-terminal case
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