Comparative analysis of low-temperature magnetic behavior in NiFe2O4 and CoFe2O4 spinel ferrite nanoparticles: soft versus hard properties

Abstract

This paper presents a comparative study of the structural, M & ouml;ssbauer, and low-temperature magnetic properties of soft NiFe2O4 (NFO) and hard-like CoFe2O4 (CFO) spinel ferrite nanoparticles (NPs) synthesized via a facile sol-gel method. The formation of the cubic spinel phase in the as-prepared NPs was confirmed through X-ray diffraction and Fourier-transform infrared spectroscopy analyses. Transmission electron microscopy revealed average particle diameters of 18 nm for NFO and 15 nm for CFO, and further selected area electron diffraction patterns corroborated the presence of the spinel structure. Magnetization vs. field (M-H) hysteresis loops were measured at nine different temperatures in the range of 2 K to 370 K under an applied field of up to 7 Tesla. These measurements revealed soft magnetic behavior for NFO, with a saturation magnetization (MS) of 30.38 emu/g and coercivity (HC) of 531 Oe, while CFO exhibited nearly hard magnetic behavior, showing an MS of 51.88 emu/g and HC of 15,956 Oe at 2 K. Based on the M-H data, we further evaluated the magnetic moment per formula unit, the first-order magnetocrystalline anisotropy constant (K1), and the cation distribution, and investigated their temperature-dependent evolution. The magnetic properties of CFO are significantly enhanced compared to NFO, primarily due to the stronger magneto crystalline anisotropy introduced by the presence of Co2+ ions. Additionally, room-temperature 57Fe M & ouml;ssbauer spectroscopy revealed the coexistence of sextet and doublet components, indicative of ferrimagnetic and superparamagnetic behavior, respectively. These findings suggest that CFO NPs, relative to NFO, possess superior magnetic characteristics, making them promising candidates for applications in optics, catalysis, and biomedicine.