Size Dependence of Metal-Insulator Transition in Stoichiometric Fe3O4 Nanocrystals

TL;DR

This study systematically investigates how the Verwey metal-insulator transition in Fe3O4 nanocrystals varies with size, revealing suppression of the transition in particles smaller than 20 nm and its disappearance below 6 nm.

Contribution

It provides the first detailed size-dependent analysis of the Verwey transition in stoichiometric Fe3O4 nanocrystals, spanning from 5 to 100 nm.

Findings

Verwey transition weakly depends on size in Fe3O4 nanocrystals.

Transition disappears in particles smaller than 20 nm.

Transition fully vanishes below 6 nm.

Abstract

Magnetite (Fe3O4) is one of the most actively studied materials with a famous metal-insulator transition (MIT), so-called the Verwey transition at around 123 K. Despite the recent progress in synthesis and characterization of Fe3O4 nanocrystals (NCs), it is still an open question how the Verwey transition changes on a nanometer scale. We herein report the systematic studies on size dependence of the Verwey transition of stoichiometric Fe3O4 NCs. We have successfully synthesized stoichiometric and uniform-sized Fe3O4 NCs with sizes ranging from 5 to 100 nm. These stoichiometric Fe3O4 NCs show the Verwey transition when they are characterized by conductance, magnetization, cryo-XRD, and heat capacity measurements. The Verwey transition is weakly size-dependent and becomes suppressed in NCs smaller than 20 nm before disappearing completely for less than 6 nm, which is a clear, yet highly interesting indication of a size effect of this well-known phenomena. Our current work will shed new light on this ages-old problem of Verwey transition.