The ferromagnetic-antiferromagnetic properties of Ni-Cr2O3 composite hollow spheres prepared by an in situ reduction method

Considerable efforts have been exerted on the facile synthesis of magnetic composite materials because of their unique properties and potential applications. Especially for ferromagnetic-antiferromagnetic systems, the magnetic exchange bias effect is essential for the development of magneto-electronic switching devices and magnetic storage media. In this research, a facile ethylene glycol in situ reduction strategy has been successfully employed in the preparation of Ni-Cr2O3 composite hollow spheres. X-Ray powder diffraction was used to determine the phase composition. Scanning electron microscopy and transmission electron microscopy was employed to characterize the morphologies of the as-prepared samples. Experiments proved that the volume ratio of ethylene glycol to water played a determinative role in the final morphology of the products. The magnetization vs. temperature results revealed a spin-glass-like behavior with blocking temperature of about 150 K for the as-prepared Ni-Cr2O3 composites. Induced by the coupling between ferromagnetic Ni and antiferromagnetic Cr2O3, a small exchange bias effect could be observed in the magnetic hysteresis loops. At lower temperature, a larger exchange bias field and coercivity are obtained. A high surface area of 145.1 m(2) g(-1) was obtained for the prepared porous hollow spheres.