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 Tv=115 K which is a little lower than the Tv value (∼120 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.

No abstract

No abstract

Co80Ir20 films with negative uniaxial magnetocrystalline anisotropy (Ku) are investigated with respect to the regularity of the stacking sequence and atomic site arrangement. Substrate heating at 600 °C enhances the negative Ku of Co80Ir20 to −9.6 × 106 erg/cm3. X-ray diffraction analysis and scanning transmission electron microscopy of the Co80Ir20 film fabricated at 600 °C indicate (1) a near perfect hexagonal-close-packed (hcp) stacking structure and (2) an atomic layered structure that consists of randomly sequenced Ir-rich and Ir-poor layers. These hcp and composition-modulated atomic layer stacking structures are considered to be the reason for the enhancement of the negative Ku.

No abstract