Influence of the Substrate and Precursor on the Magnetic and Magneto-transport Properties in Magnetite Films

摘要

We have investigated the magnetic and transport properties of nanoscaled Fe_3O_4 films obtained from Chemical Vapor Deposition (CVD) technique using [Fe~(II)Fe_2~(III)(OBu~t)_8] and [Fe_2~(III)OBu~t)_6] precursors. Samples were deposited on different substrates (i.e., MgO (001), MgAl_2O_4 (001) and Al_2O_3 (0001)) with thicknesses varying from 50 to 350 nm. Atomic Force Microscopy analysis indicated a granular nature of the samples, irrespective of the synthesis conditions (precursor and deposition temperature, T_(pre)) and substrate. Despite the similar morphology of the films, magnetic and transport properties were found to depend on the precursor used for deposition. Using [Fe~(II)Fe_2~(III)(OBu~t)_8] as precursor resulted in lower resistivity, higher M_s and a sharper magnetization decrease at the Verwey transition (Tv). The temperature dependence of resistivity was found to depend on the precursor and T_(pre). We found that the transport is dominated by the density of antiferromagnetic antiphase boundaries (AF-APB's) when [Fe~(II)Fe_2~(III)(OBu~t)_8] precursor and T_(pre) = 363 K are used. On the other hand, grain boundary-scattering seems to be the main mechanism when [Fe_2~(III)OBu~t)_6] is used. The Magnetoresistance (MR(H)) displayed an approximate linear behavior in the high field regime (H > 796 kA/m), with a maximum value at room-temperature of ～ 2-3% for H = 1592 kA/m, irrespective from the transport mechanism.