Tunneling junctions of stacked monolayers of uniform, organically functionalized ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanocrystals of 5.5 nm average diameter were prepared. Current-voltage characteristics of the junctions were studied as function of temperature and magnetic field. An abrupt increase in the resistance was observed on cooling below 96 K. This is attributed to the Verwey metal-insulator transition in the nanocrystals. Above 96 K, the $I-V$ curves reflect the density of states of the narrow conduction band. This conductance peak is sensitive to the external magnetic field and exhibits large magnetoresistance.

• Received 4 February 2002

DOI:https://doi.org/10.1103/PhysRevB.65.172405