Relationship of magnetic behavior and surface spin coupling in Hematite nanowires bundles

• α-Fe2O3 nanowires (NWs) and bundles (NWBs) were prepared in the same conditions.
• Both samples possessed the same diameter and different interwires distance.
• Ms of α-Fe2O3 NWBS was lower, while Hc and Tc of α-Fe2O3 NWBS were higher.
• Surface spin of neighboring nanowires re-coupled each other for α-Fe2O3 NWBs.
• Surface spin coupling could weaken the surface effect on magnetic properties.

Hematite (α-Fe2O3) nanowires were synthesized using mesoporous SBA-15 silica as the hard templates, and then the well-dispersed α-Fe2O3 nanowires (NWS) were separated from the ordered α-Fe2O3 nanowires bundles (NWBS) by the centrifugation technique. X-ray diffraction (XRD), transmission electron microscopy (TEM) and surperconducting quantum interference device (SQUID) were used to characterize the microstructure and magnetic properties of the as-prepared samples. All results indicated that the α-Fe2O3 NWS and NWBS with the different interwires distance presented the same diameter for nanowires, which was possible to reveal the exchange interaction between α-Fe2O3 NWBs. Both samples showed ferromagnetism and α-Fe2O3 NWS presented superparamagnetism at high temperature. The magnetic results indicated the surface spin between the neighboring nanowires of α-Fe2O3 NWBs coupled each other. The saturation magnetization of α-Fe2O3 NWBS was lower than that of α-Fe2O3 NWS, while the coercivity and Curie temperature were larger. It was concluded that the surface spin coupling could weaken the surface effect on the magnetic properties for nanostructures.

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