Basic motion of spin in ferromagnets is precession, which is
similar to oscillation of a pendulum. Precession frequency is several GHz
for the usual ferromagnetic metals, eg. iron, but it exceeds more than
100 GHz in some kinds of materials. Such a high speed motion of spins can
be applied to the high speed spin devices, such as a nano-scaled microwave
oscillator based on magnetic tunnel junctions (MTJ) or the high speed switching
for the MTJ-cell in Magnetoresistive Random Access Memory (MRAM). Thus,
the investigation of spin dynamics is of quite importance in the field
of spintronics. gAll optical pump-probe detectionh is the current state
of art technique for the investigation of spin dynamics. All optical pump-probe
detection is based on pump-probe spectroscopy with ultrafast pulse laser.
The motion of spins can be induced only by laser light pulse and any coils
or inductances, which are required to generate pulsed magnetic field in
the other techniques, are not involved in the set-up, so that one can achieve
the ultimate time resolution better than hundred femtosecond. The equivalent
frequency bandwidth of this measurement is more than 1 THz. In our laboratory
we are constructing the set-up of all optical pump-probe detection and
are investigating very fast spin dynamics for magnetic films of transition
metals, half-metals, high magnetic anisotropy materials.
Our set-up for all optical pump-probe detection using Ti:sapphire laser.
The obtained signal of spins precession for 10 nm thick Ni80Fe20 films.