Chemical Control of Superparamagnetic Properties of Magnesium and Cobalt Spinel Ferrite Nanoparticles through Atomic Level Magnetic Couplings

TLDR

Neutron diffraction reveals that Fe³⁺ lattice sites contribute similarly to magnetic anisotropy in MgFe₂O₄ and CoFe₂O₄ spinel ferrite nanoparticles, indicating comparable cation distributions. The study shows that electron spin–orbital coupling governs superparamagnetism in MgFe₂O₄ and CoFe₂O₄ nanoparticles, with CoFe₂O₄ exhibiting a blocking temperature at least 150 °C higher and greater magnetic anisotropy than MgFe₂O₄, indicating that chemical tuning of anisotropy energy can control their superparamagnetic behavior.

Abstract

A correlation between the electron spin−orbital angular momentum coupling and the superparamagnetic properties has been established in MgFe2O4 and CoFe2O4 spinel ferrite nanoparticles. The contribution to the magnetic anisotropy from the Fe3+ lattice sites is almost the same in both nanocrystallites as neutron diffraction studies have shown a similar cation distribution in these two types of spinel ferrite nanoparticles. Due to the strong magnetic couplings from Co2+ lattice sites, the blocking temperature of CoFe2O4 nanoparticles is at least 150 deg higher than the same sized MgFe2O4 nanoparticles. Mössbauer spectroscopy studies demonstrate that the magnetic anisotropy of CoFe2O4 nanoparticles is higher than that of the same size MgFe2O4 nanoparticles. These studies indicate that the superparamagnetic properties of nanoparticles can be controlled through chemically adjusting the magnetic anisotropy energy.