Silicide Induced Surface Defects in FePt nanoParticle fcc-to-fct Thermally Activated Phase Transition

TL;DR

This study investigates how silica shells influence the phase transition and surface defects in FePt magnetic nanoparticles during thermal annealing, revealing silicide formation that hampers magnetic property enhancement.

Contribution

It uncovers the formation of silicide due to silica shells during annealing, highlighting a previously underexplored interfacial phenomenon affecting magnetic properties of FePt nanoparticles.

Findings

Silica shells prevent sintering during annealing.

fcc-to-fct phase transition occurs despite silicide formation.

Silicide formation impairs magnetic property enhancement.

Abstract

Magnetic nanoparticles (MnPs) are relevant to a wide range of applications including high density information storage and magnetic resonance imaging to name but a few. Among the materials available to prepare MnPs, FePt is attracting growing attention. However, to harvest the strongest magnetic properties of FePt MnPs, a thermal annealing is often required to convert face-centered cubic as synthesized nPs into its tetragonal phase. Rarely addressed are the potential side effects of such treatments on the magnetic properties. In this study, we focus on the impact of silica shells often used in strategies aiming at overcoming MnP coalescence during the thermal annealing. While we show that this shell does prevent sintering, and that fcc-to-fct conversion does occur, we also reveal the formation of silicide, which can prevent the stronger magnetic properties of fct-FePt MnPs from being fully realised. This report therefore sheds lights on poorly investigated and understood interfacial phenomena occurring during the thermal annealing of MnPs and, by doing so, also highlights the benefits of developing new strategies to avoid silicide formation.