Magnetic properties and Verwey transition of quasi-one-dimensional magnetite nanowire arrays assembled in alumina templates

Magnetite (Fe3O4) has been successfully assembled into anodic alumina templates by an electrochemical method followed by a heat-treating process. Here, we report on the magnetic properties of these so formed nanowires and the Verwey transition measured by vibrating sample magnetometer and SQUID. A Mossbauer spectrum was collected to verify the magnetic orientation of the wires, and a tilt of the moment of 45 degrees with respect to the wire axis was found. These wires show perpendicular magnetic anisotropy mainly due to the average easy axis of the grains pointing along the wire axis. The temperature dependence of the coercity, remanence, and the magnetization undergo a major change at 50 K, induced by the Verwey transition, which occurs at a temperature much lower than for bulk materials (120 K). The behavior of the magnetization in the vicinity of 50 K as well as its field-dependent properties was interpreted using the magneto-electronic model. (c) 2004 Elsevier B.V. All rights reserved.