  Ultrafast demagnetization in magnetic nanoparticles using pulsed laser has
attracted considerable attention because of its potential applications in
spintronics, such as data storage. In such applications, it is necessary to
control magnetization using low energy laser pulses, however, this poses the
problem of increasing the amount of energy from the excitation laser pulses to
the spin subsystem. We take advantage of the phenomenon known as localized
surface plasmon resonance (LSPR) to enhance the energy transfer from laser
pulses to the spin subsystem. To induce LSPR, hybrid nanoparticles consisting
of noble metal nanoparticles with LSPR absorption and magnetic metal
nanoparticles are prepared using a novel method. Specifically, AgCo hybrid
nanoparticles are prepared by a self assembly method using pulsed laser
deposition. We performed measurements of the static Faraday and time-resolved
Faraday effects using a pump probe technique on the AgCo hybrid nanoparticles
with various AgCo ratios. The data suggest that the LSPR absorption and
demagnetization amplitude increase with the increasing AgCo ratio. The results
indicate that the amount of energy transferred from the laser pulses to the
spin system of magnetic nanoparticles can increase via LSPR absorption.
