We have systematically studied the evolution of magnetic properties, especially the coercivity and the remanence ratio in the vicinity of the Verwey transition temperature (TV ), of high-quality epitaxial Fe3O4 thin films grown on MgO (001), MgAl2O4 (MAO) (001), and SrTiO3 (STO) (001) substrates.We observed rapid change of magnetization, coercivity, and remanence ratio at TV , which are consistent with the behaviors of resistivity versus temperature [ρ(T )] curves for the different thin films. In particular, we found quite different magnetic behaviors for the thin films on MgO from those on MAO and STO, in which the domain size and the strain state play very important roles. The coercivity is mainly determined by the domain size but the demagnetization process is mainly dependent on the strain state. Furthermore, we observed a reversal of remanence ratio at TV with thickness for the thin films grown on MgO: from a rapid enhancement for 40-nm-to a sharp drop for 200-nm-thick film, and the critical thickness is about 80 nm. Finally, we found an obvious hysteretic loop of coercivity (or remanence ratio) with temperature around TV , corresponding to the hysteretic loop of the ρ(T ) curve, in Fe3O4 thin film grown on MgO.

A three‐dimensional molybdenum‐carbides/graphite network formed by superconducting MoC/Mo2C nanograins embedded in a magnetic graphite matrix was fabricated. The temperature dependence of magnetization of the MoC/Mo2C nanocomposites indicates that the superconducting transition temperatures (TC) of Mo2C and MoC nanocrystals are 8 K and 11.5 K, respectively. These transition temperatures are lower than those of their corresponding bulk counterparts, due to the detrimental influence of magnetic graphite. The magnetization influenced by edge barrier and magnetic graphite are investigated for the MoC/Mo2C nancomposites embedded in the magnetic graphite matrix. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)