Co₃O₄-γ-Fe₂O₃Nanocrystal Heterostructures with Enhanced Coercivity and Blocking Temperature

Abstract

Reassembly of α-cobalt hydroxide nanosheets in the presence of citrate-capped γ-Fe 2 O 3 nanoparticles yields α-cobalt hydroxide−γ-Fe 2 O 3 hybrid in which the nanoparticles are trapped between the nanosheets. Thermal decomposition of the hybrid yields the Co 3 O 4 −γ-Fe 2 O 3 heterostructure. While the saturation magnetization (M s ) of γ-Fe 2 O 3 is preserved in the Co 3 O 4 −γ-Fe 2 O 3 heterostructure, the interface between the oxides in the heterostructure enhances the coercive field (H C ) to a large extent. The coercivity persists even above the Neél temperature of Co 3 O 4 with the blocking temperature increased beyond room temperature. The unique morphology of the heterostructure wherein the Co 3 O 4 and γ-Fe 2 O 3 particles are fused together to form a larger network leading to strong interparticle interactions, diffusion of Co atoms into the surface of γ-Fe 2 O 3 particles, and strain at the interfaces appear to be the reasons behind the improved magnetic behavior.