Tailoring magnetic properties with interfacial spins interaction for bundled cobalt ferrites nanowires

Bundled cobalt ferrites (CoFe2O4) nanowires (BNWs) were successfully prepared by nanocasting pathway with ordered mesoporous SiO2 (SBA-15) templates. The well-dispersed CoFe2O4 nanowires (NWS) were separated from CoFe2O4 BNWs by centrifugal technology. Microstructure characterization indicated that CoFe2O4 BNWs and NWS possessed the same diameter and similar length. Thus, the influence of surface spins interaction between neighboring nanowires on the magnetic properties could be distinguished and discussed excluding the difference of morphology. Both samples presented ferromagnetism with the wasp-waisted hysteresis loops and the exchange bias effect was observed above 100 K. The surface spins interactions between the neighboring nanowires not only recombined the mismatch spins at the surface to form antiferromagnetic surface, but also inhibited the shape anisotropy of nanowires, leading to the decrease of saturation magnetization and coercivity of CoFe2O4 BNWs. The wasp-waisted hysteresis loops was attributed to the low temperature spin reorientation caused by the inclined spin on the surface of nanowires.