ChargeorderingandexchangebiasbehaviorsinCo3O4 porous nanoplatelets and nanorings

Abstract

We present the synthesis of α-Co3O4 porous nanoplatelets and hexagonal nanorings using microwave- assisted hydrothermal and conventional chemical reaction methods. The x-ray diffraction(XRD) and refinement analyses indicate the α-Co3O4 crystal structure, and the x-ray photo electrons pectrum (XPS) indicates the high purity of the samples. The M–T (including1/χ–T) curves indicate an antiferromagnetic transition at about 35K in both kind of samples but the interesting finding was made that a charge- ordered(CO) state appears at 250K for the nanoplatelets sample whereas it is inattentive for the na-norings. The antiferromagnetic transition temperature TN is lower than that of the bulk α-Co3O4 single crystal due to the nanosized structures. We observed quite significant exchange bias for nanorings. The exchange bias behavior of the α-Co3O4 hexagonal nanorings is consistent with an antiferromagnetic (AFM) Co3O4 core and spin-glass like shell.