Low-temperature magnetic properties of hematite nanorods

Low-temperature magnetic properties of hematite nanorods, prepared by both iron-water vapor reactions (sample 1) and hydrothermal methods (sample 2), were studied by superconducting quantum interference device (SQUID) magnetometry. The Morin transition temperature was found to be 122 K in hematite nanorod sample 1, and an unexpected phenomenon was found under an applied field of 10 Oe. These nanorods (sample 1) show an abrupt decrease of the magnetic susceptibility at ca. 122 K, contrary to the abrupt increase normally attributed to the Morin transition in bulk hematite. The origin of this phenomenon can be traced to the probable coherence of the one-dimensional shape anisotropy with the magnetocrystalline anisotropy. In contrast, no obvious Morin transition was found in hematite nanorod sample 2.