Abstract
The present work reports the magnetic effect of particle shape and magnetic property in a Co/CoO core-shell exchange bias system. Co/CoO core-shell nanoparticles/spheres (NPSs) of different sizes including spherical and octahedral morphologies were prepared by the decomposition of cobalt acetate under eco-friendly solvothermal conditions. Spherical and octahedral Co/CoO NPSs all display superparamagnetism at room temperature due to the superparamagnetic critical size of cobalt. And it can be seen in hysteresis loop patterns that the saturation magnetization (MS) values of the Co/CoO NPSs are 100.6, 76.1, and 75.9 emu/g, whose diameters are about 16, 200 and 300 nm, respectively. In addition, all of spherical Co/CoO NPSs reveal exchange bias field at low temperature, whereas octahedral ones disappear because excessive PVP inhibits the formation of exchange coupling interface between ferromagnetic Co and antiferromagnetic CoO. These results were only observed after field cooling at 5 T.
Highlights
Exchange bias (EB) effect occurs at the interface between ferromagnetic (FM) materials and antiferromagnetic (AFM) materials due to the exchange anisotropy.[1,2] Magnetic hysteresis loops of FM/AFM materials shift along the external filed axis when the system is field-cooled from high temperature.[3,4] With the rapid development of the giant magnetoresistance effect and spintronic devices, the EB effect has been one of the hotspots of magnetism
We present the direct evidence of the magnetic effect of particle shape and magnetic property in a Co/CoO core-shell EB system
We demonstrated three different crystalline morphology and structure of Co/CoO NPSs including spherical and octahedral morphology, whose sizes are 16, 200 and 300 nm, respectively
Summary
Exchange bias (EB) effect occurs at the interface between ferromagnetic (FM) materials and antiferromagnetic (AFM) materials due to the exchange anisotropy.[1,2] Magnetic hysteresis loops of FM/AFM materials shift along the external filed axis when the system is field-cooled from high temperature (above AFM Neel temperature TN but below than FM Curie temperature TC).[3,4] With the rapid development of the giant magnetoresistance effect and spintronic devices, the EB effect has been one of the hotspots of magnetism. Various arrangements and shapes of Co/CoO systems were extensively explored about EB effects.[5,6,7,8,9] For the Co/CoO core-shell nanoparticles/spheres (NPSs) model, the main features of EB fields were observed, including inverse relationship with the FM layer thickness, positive relationship with the AFM layer thickness, strong dependency on the interface structure, and etc.[10,11,12,13] But so far the researches into the effect of NPSs shape and magnetic property have rarely appeared in the literatures.[14]
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