Magnetic, electrical and induction heating properties of magnetite/hematite mixed phase nanoparticles

Abstract

Iron oxides in nanoform are associated with exciting properties for various applications such as energy storage, magnetic recording, biomedicine and sensing. These applications demand the tuning of the physico-chemical properties of iron oxide especially Fe₃O₄ phase. However, iron oxides generally exist in mixed phases of any of its mostly occurred three phases magnetite, maghemite and hematite. Here, we report a solvothermally processed mixed phase of magnetite and hematite nanoparticles (NPs) which has been prepared using P123 triblock copolymer in addition to urea and hexamethylenetetramine (HMTA). The magnetite phase crystallizes in inverse spinel structure of Fe₃O₄ whereas hematite (α-Fe₂O₃) phase crystallizes in corundum structure. The use of copolymer leads to flake-shaped morphology of nanoparticles whereas use of urea and HMTA in different ratio gives different proportion of magnetite and hematite. The mixed iron oxide nanoparticles (IONPs) possess significantly different magnetic, electrical and dielectric properties than their bulk analogue. The surface analysis confirms the presence of magnetite and hematite phase in all the samples attributed to the coexistence of Fe³⁺ and Fe²⁺ ions. FESEM micrographs shows evenly distributed nanoparticles but in aggregated form. Furthermore, due to their weakly ferromagnetic behaviour with magnetisation value of ∼55 emu/g at 1.5 kOe field, the nanoparticles exhibited good induction heating behaviour under AC magnetic field. As high as 472 W/g of specific absorption rate was attained at a nanoparticle concentration of 1 mg/mL in water.