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, Ag-Co 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 Ag-Co hybrid nanoparticles with various Ag-Co ratios. The data suggest that the LSPR absorption and demagnetization amplitude increase with the increasing Ag-Co 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.

We investigated the structural variation of Ag–Co nanostructures in AgxCo5(TiO2)95 nanocomposite films with varying pulsed laser deposition conditions. The shape, size, and distribution of the nanostructures were significantly affected by the Ag content (x) and the substrate temperature. Ag–Co nanomatch-like structures appeared only at a specific condition and changed from rod-like to spherical with increasing x. A broad peak owing to Ag local-surface plasmon resonance was observed in the absorption spectra, which systematically shifted to longer wavelengths with increasing x.

Nanocomposite thin films consisting of Co nanorods and an anatase TiO2 matrix were successfully prepared by pulsed laser deposition (PLD). Co nanorods with diameters of 9−6 nm and heights of 10−22 nm were homogeneously dispersed in the matrix as a result of phase separation during PLD growth. Magnetization measurements confirmed ferromagnetic signals comparable to those expected for Co metal, suggesting that because of the high oxygen affinity of Ti, oxidation of Co nanorods did not occur. The obtained nanocomposite films were highly transparent in the visible-light region and had a ferromagnetic Faraday ellipticity of 1.9 × 104 deg cm−1 at 3.5 eV.

No abstract