Abstract.
In the “pump-probe”
scheme the task for three-layers structure is investigated. This structure
consist of thick substrate (buffer slide) on the two surfaces of which are
applied two films, first of which has high thermal expansion coefficient and
second has high magnetoelastic properties. The influence of light pulse to the
first film in connection with thermal expansion excites in its intensive
elastic vibrations. These vibrations after the passing of buffer slide reach
the second film and excite in its by means of magnetostriction the intensive
magnetic vibrations. It is found the connected nonlinear movement excitations
of magnetization and elastic displacement in the case of frequency equality of
magnetic and elastic resonances. It is investigated the development in time of
elastic and magnetic vibrations in supposition that the most role in magnetic
vibrations plays the form of last front of elastic displacement pulse. It is
investigated three possible versions of last front of elastic displacement
pulse forming: regimes of small, middle and large dissipation. It is shown that
in small dissipation regime on the last front of elastic pulse it is excited
the intensive elastic vibrations which frequency is equal to resonance and
amplitude is in several cases more then amplitude of initial pulse. In this
case in the initial moment of elastic pulse there is excited the intensive
magnetic vibrations which frequency is determined by summary action of external
field and the magnetostriction field. After the end of elastic pulse the
magnetic vibration frequency sharp increases and amplitude acquires the
nonpermanent character similar to chaotic. After the increasing of free elastic
vibrations are finished the magnetic vibrations are regularized and relax with
own frequency in correspondence with own relaxation time. In the middle elastic
dissipation regime on the last front of elastic displacement pulse it is formed
the sharp abatement accompanied by one-two periods of free vibrations after
which the elastic vibrations are dissipated. In this case in the first moment
of elastic pulse the intensive magnetic vibrations are excited which are the
same as in the previous case. After the end of elastic pulse the magnetic
vibrations are emancipate from elastic displacement influence and relax on own
frequency in correspondence with own relaxation time. In the large elastic
dissipation regime on the end front of elastic pulse is formed the smooth
decreased elastic displacement having unperiodical character which decreasing
time considerably exceeds the time of free vibrations period. In this case in
the initial moment of elastic pulse the intensive magnetic vibrations are
excited which are the same as in the previous cases. After the end of elastic
pulse the magnetic vibrations frequency smooth approaches to zero. It is
investigated the influence to magnetic plate by limited series of successive
following one after the other elastic pulses having intervals between each
other equal to duration of pulses ones. The investigation is made for the same
three values of elastic dissipation – small, middle and large ones. It is shown
that, in the case of small dissipation, each newly arriving elastic pulse
forces its own amplitude to elastic vibrations excited by previous pulse. In
this case the magnetic vibrations during all the time of elastic pulses
succession have high frequency and its amplitude has the nonpermanent character
similar to chaotic. In the case of middle dissipation the following one after
the other elastic pulses are independent each from other so the elastic displacement
actions are periodically repeated. The magnetic vibrations also repeat its own
development periodically in the correspondence to the vibrations excited by
solitary pulse. In the case of large dissipation the elastic displacement which
is excited by preceding pulse to the moment of following pulse arrival does not
found time of relaxation. As a result there take place the smooth accumulation
of elastic displacement with corresponding increase of elastic pulses effective
amplitude. The most frequency of magnetic vibrations corresponded to beginning
of each elastic pulse also smooth increase what is reflected by elastic
displacement amplitude growth. It is described some recommendations for
practical application of observed phenomenon. As an example of important
application it is drew attention to the possibility of creation very high
frequency electromagnetic vibrations generator hawing small magnetic system.
Key words:
method “pump-probe”,
femtosecond laser, magnetoelastic interaction, elastic relaxation, magnetic
relaxation.
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