Charge ordering and exchange bias behaviors in Co3O4 porous nanoplatelets and nanorings

●Charge-ordered state appears for the Co3O4 nanoplatelets but absent for the nanorings.●Quite significant exchange bias is only observed for Co3O4 nanorings.●Exchange bias behavior of Co3O4 nanorings is consistent with spin-glass like shell.●Potential for ultrahigh-density magnetic recording and spin valve devices.

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 photoelectron spectrum (XPS) indicates the high purity of the samples. The M–T (including 1/χ–T) curves indicate an antiferromagnetic transition at about 35 K in both kind of samples but the interesting finding was made that a charge-ordered (CO) state appears at 250 K for the nanoplatelets sample whereas it is inattentive for the nanorings. 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.