Surface effects and spin glass state in Co3O4 coated MnFe2O4 nanoparticles

Abstract

Surface effects and spin glass state have been studied in Co3O4 coated manganese ferrite (MnFe2O4) nanoparticles by using AC and DC magnetic measurements. Average crystallite size of Co3O4 coated MnFe2O4 nanoparticles was 7 nm as calculated by Debye-Scherrer's formula. Simulated ZFC/FC revealed higher value of effective anisotropy (Keff) = 5 106 erg cm-3 of these nanoparticles as compared to bulk MnFe2O4 due to enhanced surface effects. Temperature dependent saturation magnetization followed the Bloch's law. Temperature dependent coercivity showed sharp increase below 25 K due to strong surface anisotropy and exchange coupling at interface between ferrimagnetic core and antiferromagnetic surface. For frequency dependent AC-susceptibility, dynamic scaling law fit confirmed the spin glass behavior in Co3O4 coated MnFe2O4 nanoparticles. DC field dependent AC-susceptibility showed the suppression of energy barrier, reduced activation energy and decreased strength of interparticle interactions with increasing DC field. Slow spin relaxation in ZFC protocol further confirmed the presence of spin-glass behavior. All this analysis confirmed the existence of spin-glass behavior as attributed to disordered surface spins and interparticle interactions in these nanoparticles, which gets suppressed after the application of moderate DC field.