Effective magnetic moment of magnetic multicore nanoparticles

Abstract

We carry out Monte Carlo simulations to study the effective magnetic moment ${\ensuremath{\mu}}_{\text{eff}}$ in the low-field region of magnetic multicore nanoparticles. Transmission electron microscopy and scanning electron microscopy images show that these particles contain a number of magnetic nanocrystals (MNCs) randomly packed in a single cluster of total volume ${V}_{\text{tot}}$. We illustrate how the initial magnetic susceptibility ${\ensuremath{\chi}}_{0}$ of magnetic multicore nanoparticles can be straightforward derived from ${\ensuremath{\mu}}_{\text{eff}}$ computed at zero magnetic field. We observe that dipolar interactions between MNCs and polydispersity of the MNCs contribute to increase and to decrease ${\ensuremath{\mu}}_{\text{eff}}/{V}_{\text{tot}}$, respectively, while magnetic anisotropy of the MNCs does not show any effect. In all three cases, ${\ensuremath{\mu}}_{\text{eff}}/{V}_{\text{tot}}$ can be described by a linear relation to ${(\ensuremath{\mu}B/{k}_{B}T)}^{2}$ that we analytically derived for low applied fields.