Domain controlled magnetic and electric properties of variable sized magnetite nano-hollow spheres

Abstract

Here, we report the synthesis of variable sized magnetite (Fe3O4) nano-hollow spheres in one step template free solvothermal method and their size dependent magnetic and electrical properties. Size of the hollow spheres is varied from 100 nm to 725 nm by changing the concentration of capping agent. Trace of Verway transition is found for all sets of spheres and the Verway transition temperature (TV) increases with increasing size of the spheres. The domain structure of these spheres changes from pseudo single domain to multi domain state as the size increases from 100 nm to 725 nm as evident from Day plots. This change in domain structure also changes the magnetic and electric properties of these spheres. Temperature dependent of high field magnetization of the hollow spheres can be well explained by Bloch's power law with higher than the bulk value of Bloch constant. The Bloch exponent varies from 1.94 to 1.69 with increasing size of the spheres. Frequency dependence of electrical conductivity (σ) shows Jonscher's power law type behaviour and bigger spheres are found to be more conductive than smaller ones due to their multidomain configuration.