Magnetic properties and magnetoresistance in small iron oxide cluster assemblies

We report the magnetic properties and magnetoresistance (MR) in small iron oxide (Fe3-xO4 and Fe3O4) cluster assemblies. Half-metallic Fe3O4 cluster assembly with grain size of 10-15 nm is shown to exhibit a MR value of about 8% at T=30 K and a peak around the Verwey transition temperature T-v=115 K which is a little lower than the T-v value (similar to120 K) of single crystal specimens. Even at T=5 K, the magnetization is not saturated in fields up to 50 kOe. The MR behaviors of a Fe3-xO4-coated iron cluster assembly and a sample which was prepared by embedding the Fe3-xO4-coated iron clusters into a MgO matrix are also studied for comparison. The MR value of the latter is over one time larger than that of the former and is also larger than those of the Fe3O4 cluster assembly at various temperatures. It suggests that the barrier layer is important for enhancing the MR effect at high temperatures. (C) 2002 American Institute of Physics