Quantitative measurements of size-dependent magnetoelectric coupling in Fe3O4 nanoparticles

摘要

Bulk magnetite (Fe3O4), the loadstone used in magnetic compasses, has beenknown to exhibit magnetoelectric (ME) properties below ~10 K; however,corresponding ME effects in Fe3O4 nanoparticles have been enigmatic. Weinvestigate quantitatively the ME coupling of spherical Fe3O4 nanoparticleswith uniform diameters (d) from 3 to 15 nm embedded in an insulating host,using a sensitive ME susceptometer. The intrinsic ME susceptibility (MES) ofthe Fe3O4 nanoparticles is measured, exhibiting a maximum value of ~0.6 ps/m at5 K for d=15 nm. We found that the MES is reduced with reduced d but remainsfinite until d=~5 nm, which is close to the critical thickness for observingthe Verwey transition. Moreover, with reduced diameter, the criticaltemperature below which the MES becomes conspicuous increased systematicallyfrom 9.8 K in the bulk to 19.7 K in the nanoparticles with d=7 nm, reflectingthe core-shell effect on the ME properties. These results point to a newpathway for investigating ME effect in various nanomaterials.