Enhancement of Magnetization through Interface Exchange Interactions of Confined NiO Nanoparticles within the Mesopores of CoFe2O4

Abstract

A bimagnetic nanostructure was designed where the antiferromagnetic (AFM) NiO nanoparticles (NPs) are confined within the pores of a mesoporous ferrimagnetic (FiM) CoFe2O4 matrix. An amount of 3.4 wt % of 9 ± 1 nm NiO NPs was inserted into pores of 35 ± 5 nm clustered CoFe2O4 NPs when the −NH3+ groups of cysteamine on the NiO NP surface electrostatically bind to the −OSO3– of sodium dodecyl sulfate (SDS) attached to CoFe2O4 NPs. The role of in situ embedded NiO NPs is 3-fold: (i) to nearly double the saturation magnetization (MS) and coercivity (HC) by suppressing the frozen disordered spins on the surface of CoFe2O4 NPs surrounding the NiO NPs inside the pores at the cost of enhanced FiM ordering, (ii) to introduce AFM/FiM exchange coupling by breaking the spin glass surface layer to provide exchange bias (EB) of 233.0 ± 0.2 Oe at 5 K with a cooling field of 2 T, and (iii) to provide symmetry to the asymmetric nature of the hysteresis loop of CoFe2O4. In the absence of cooling field, the pristine CoFe2O4...