THESIS
2016
xiv, 88 pages : illustrations (some color) ; 30 cm
Abstract
In this thesis, the interplay of spin waves and domain walls in magnetic nanostructures is
studied in three aspects: (1) how a domain wall can propagate in a magnetic field through
emitting spin waves, (2) how an externally generated spin wave can drive a domain wall’s
propagation, whose mechanism is called “all-magnonic spin transfer torque”, and (3) how spin
wave excitations affect the thermodynamic properties of a domain wall system and drive the
domain wall propagation in a temperature gradient.
We theoretically study field-induced domain wall motion in an electrically insulating ferromagnet
with hard- and easy-axis anisotropies. Domain walls can propagate along a dissipationless
wire through spin wave emission locked into the known soliton velocity at low fields. In
th...[
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In this thesis, the interplay of spin waves and domain walls in magnetic nanostructures is
studied in three aspects: (1) how a domain wall can propagate in a magnetic field through
emitting spin waves, (2) how an externally generated spin wave can drive a domain wall’s
propagation, whose mechanism is called “all-magnonic spin transfer torque”, and (3) how spin
wave excitations affect the thermodynamic properties of a domain wall system and drive the
domain wall propagation in a temperature gradient.
We theoretically study field-induced domain wall motion in an electrically insulating ferromagnet
with hard- and easy-axis anisotropies. Domain walls can propagate along a dissipationless
wire through spin wave emission locked into the known soliton velocity at low fields. In
the presence of damping, the usual Walker rigid-body propagation mode can become unstable
for a magnetic field smaller than the Walker breakdown field. We also numerically investigate
the properties of spin waves emitted by the domain wall motion, such as frequency and
wave number, and their relation with the domain wall motion. For a wire with a low transverse
anisotropy and in a field above a critical value, a domain wall emits spin waves to both sides
(bow and stern), while it oscillates and propagates at a low average speed. For a wire with a
high transverse anisotropy and in a weak field, the domain wall emits mostly stern waves, while
the domain wall distorts itself and the domain wall center propagates forward like a drill at a
relative high speed.
The spin wave transportation through a transverse magnetic domain wall in a magnetic
nanowire is studied. It is found that in a 1D nanowire, the spin wave passes through a domain
wall without reflection. A magnon, the quantum of the spin wave, carries opposite spins on the
two sides of the domain wall. As a result, there is a spin angular momentum transfer from the
propagating magnons to the domain wall. This magnonic spin transfer torque can efficiently
drive a domain wall to propagate in the opposite direction to that of the spin wave.
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