Quantitative measurements of size-dependent magnetoelectric coupling in Fe3O4 nanoparticles

TL;DR

This study quantitatively measures size-dependent magnetoelectric coupling in Fe3O4 nanoparticles, revealing how size influences the ME susceptibility and critical temperature, providing insights into nanoscale ME effects.

Contribution

It presents the first systematic measurement of ME susceptibility in Fe3O4 nanoparticles across different sizes, highlighting the size and core-shell effects on ME properties.

Findings

MES peaks at 0.6 ps/m for 15 nm particles at 5 K

MES remains finite down to 5 nm diameter

Critical temperature for ME effects increases with decreasing size

Abstract

Bulk magnetite (Fe3O4), the loadstone used in magnetic compasses, has been known to exhibit magnetoelectric (ME) properties below ~10 K; however, corresponding ME effects in Fe3O4 nanoparticles have been enigmatic. We investigate quantitatively the ME coupling of spherical Fe3O4 nanoparticles with uniform diameters (d) from 3 to 15 nm embedded in an insulating host, using a sensitive ME susceptometer. The intrinsic ME susceptibility (MES) of the Fe3O4 nanoparticles is measured, exhibiting a maximum value of ~0.6 ps/m at 5 K for d=15 nm. We found that the MES is reduced with reduced d but remains finite until d=~5 nm, which is close to the critical thickness for observing the Verwey transition. Moreover, with reduced diameter, the critical temperature below which the MES becomes conspicuous increased systematically from 9.8 K in the bulk to 19.7 K in the nanoparticles with d=7 nm, reflecting the core-shell effect on the ME properties. These results point to a new pathway for investigating ME effect in various nanomaterials.