Synthesis, structure and magnetic properties of Fe@Pt core-shell nanoparticles

Kelly L. Pisane; Sobhit K. Singh; Mohindar S. Seehra

doi:10.1063/1.4908304

paper

Synthesis, structure and magnetic properties of Fe@Pt core-shell nanoparticles

arXiv:1502.00888 · doi:10.1063/1.4908304

Abstract

Structural and magnetic properties of Fe@Pt core-shell nanostructure prepared by a sequential reduction process are reported. Transmission electron microscopy (TEM) shows nearly spherical particles fitting a lognormal size distribution with $D$ $_{o}$ = 3.0 nm and distribution width $λ$ $_{D}$ = 0.31. In x-ray diffraction, Bragg lines due to Pt shell only are clearly identified with line-widths yielding crystallite size =3.1 nm. Measurements of magnetization $M$ vs. $T$ (2 K - 350 K) in magnetic fields up to 90 kOe show a blocking temperature $T$ $_{B}$ = 13 K below which hysteresis loops are observed with coercivity $H$ $_{C}$ increasing with decreasing $T$ reaching $H$ $_{C}$ = 750 Oe at 2 K. Temperature dependence of the ac susceptibilities at frequencies $f$ $_{m}$ = 10 Hz to 5 kHz is measured to determine the change in $T$ $_{B}$ with $f$ $_{m}$ using Vogel-Fulcher law. This analysis shows the presence of significant interparticle interaction, the Néel-Brown relaxation frequency $f$ $_{o}$ = 5.3 x 10 $^{10}$ Hz and anisotropy constant $K$ $_{a}$ =3.6 x10 $^{6}$ ergs/cm $^{3}$ . A fit of the $M$ vs. $H$ data up to $H$ = 90 kOe for $T$ $>$ $T$ $_{B}$ to the modified Langevin function taking particle size distribution into account yields magnetic moment per particle consistent with the proposed core-shell structure; Fe core of 2.2 nm diameter and Pt shell of 0.4 nm thickness.

Accepted for publication: Journal of Applied Physics

References in corpus (1)

Structural and Magnetic Properties of CoO-Pt core-shell nanoparticles