Control of magnetic behavior in Fe/sub 3/O/sub 4/ nanostructures

Hexagonally well-ordered nanoporous anodized aluminum oxide (AAO) templates were synthesized by electrochemical method. Then, magnetite (Fe/sub 3/O/sub 4/) nanoparticles of 8-15-nm diameter were filled in the pores of the AAO template, and then the morphology and magnetic properties were characterized. Vibrating sample magnetometer measurement indicated that the nanoparticles inside AAO showed superparamagnetic behavior at as-filled state. But after annealing at 600/spl deg/C for 2 hr, the nanostructure (i.e., an assembly of nanoparticles) exhibited coercivity of 80 Oe. Superconducting quantum interference measurement device data showed that after annealing the blocking temperature was above 300 K. Thus, the annealed magnetite nanostructures possessed ferrimagnetism.