Magnetic transitions in alpha-Fe_2O_3 nanowires

Abstract

Magnetic transitions in single-crystal alpha-F_2O_3 (hematite) nanowires, grown by thermal oxidation of iron powder, have been studied in the range of 5-1023 K with a superconducting quantum interference device below room temperature and with a vibrating sample magnetometer at higher temperatures. The broad temperature range covered enables us to compare magnetic transitions in the nanowires with the transitions reported for bulk hematite. Morin temperatures (T-M) of the nanowires and of hematite bulk reference powder were found to be 123 and 263 K, respectively. Also the Neel temperature (T-N) of the nanowires, 852 K, was lower than the bulk T-N value. Measurements of the magnetization as a function of temperature show an enhanced signal in the nanowires, which suggests a decrease in the anti ferromagnetic coupling. A coercive field observed below T-M in the hysteresis loops of the nanowires is tentatively explained by the presence of a magnetic phase.