Self-assembly and plasmon-enhanced ultrafast magnetization of Ag–Co hybrid nanoparticles

Abstract

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.

Magnetoplasmonics and Femtosecond Optomagnetism at the Nanoscale

“…In these conditions, a pump fluence as low as 0.06 mJ/cm 2 (i.e., 2 orders of magnitude lower than the typical values) could reduce the magnetization by 1%, as shown by the transient ellipticity detected in the Faraday geometry. 95 More remarkably, the recovery dynamics takes place on two time-scales, a short one (2 ps) and a longer one (10 ps). This is in striking contrast with the previous observations in homogeneous magnetic nanoparticles, 91−94 in which a fast recovery has never been reported.…”

“…Nanoparticles of Fe 3 O 4 and Co revealed demagnetization times comparable with thin films, but much longer recovery time (several hundreds of picoseconds). 91−94 In this framework, we would like to point out an interesting experiment, 95 addressing the issue of the energy efficiency of the demagentization process. Hybrid nanoparticles of Co and Ag were produced in a TiO 2 matrix with different concentrations of Ag, which resulted in different sizes of the Co particles.…”

“…Although a complete and conclusive discussion of the ultrafast demagnetization in hybrid nanoparticles is still missing, a scenario has been suggested. 95 The electronic excitations in the Ag nanoparticles are expected to thermalize in less than 50 fs, 95 so that the Co nanoparticles have an additional channel for ultrafast energy and heat dissipation in comparison with homogeneous nanoparticles. This process was indicated as the origin of the fast recovery dynamics.…”

Strain, magnetic anisotropy, and composition modulation in hybrid metal–oxide vertically assembled nanocomposites

“…The potential of self-assembly to yield embedded metallic columns with tunable optical resonances has been recognized early on 46,47 and was recently renewed for VANs. 16,48 Coupling of these plasmonic features with magnetic properties might turn VANs into a beautiful playground for magnetophotonic studies at the nanoscale, 49 especially in an ultrafast regime, 50 where fascinating nonequilibrium phenomena such as sub-picosecond demagnetization 51 and all optical switching 52 can be triggered by optical femtosecond pulses.…”

Spatial correlation of embedded nanowires probed by X-ray off-Bragg scattering of the host matrix

“…Examples of complex structures include, for instance, vertically aligned ZnO nanowires (NWs) capped by Au nanoparticles embedded in a piezoelectric BaTiO 3 matrix for tuning of optical properties (Misra et al, 2020), and Ag nanorods on top of Co particles and capped by Co nanoclusters in a TiO 2 matrix for photocatalysis (Watanabe et al, 2014). Further axial structuration along NWs can be envisaged, for instance within the perspective of ultrafast photo-assisted magnetization switching in ferromagnetic NWs capped by plasmonic nanoclusters (Ikemiya et al, 2014;Xu et al, 2015;Pancaldi et al, 2019).…”