Fabrication and magnetoresistance of tunnel junctions using half-metallic Fe3O4

Magnetite $({\mathrm{Fe}}_3{\mathrm{O}}_4)$ is believed to be half metal, providing 100% spin-polarized conduction electrons. The half-metallic nature of magnetic electrodes for tunneling junction devices is expected to induce a large magnetoresistance. We investigated the structural and chemical properties of interfaces in ferromagnet–insulator–ferromagnet $({\mathrm{Fe}}_3{\mathrm{O}}_4/\mathrm{MgO}/\mathrm{Fe})$ tunnel junctions. $\mathrm{Al}/\mathrm{Ag}/{\mathrm{Fe}}_3{\mathrm{O}}_4/\mathrm{MgO}$ multilayers for magnetic tunnel junction have been fabricated on $\mathrm{\alpha -}{\mathrm{Al}}_2{\mathrm{O}}_3$ (001) and MgO (100) substrates by a molecular beam epitaxy system. The ${\mathrm{Fe}}_3{\mathrm{O}}_4$ quality was examined by reflection high-energy electron diffraction (RHEED), x-ray diffraction (XRD), superconducting quantum interference device magnetometry, atomic force microscopy (AFM), and in situ x-ray photoelectron spectroscopy. RHEED and XRD results showed that the epitaxial ${\mathrm{Fe}}_3{\mathrm{O}}_4$ layer with a smooth surface was successfully grown on substrates. The stoichiometric ${\mathrm{Fe}}_3{\mathrm{O}}_4$ was confirmed by Verway transition in temperature dependence of magnetization. AFM data showed relatively smooth surface for ${\mathrm{Fe}}_3{\mathrm{O}}_4$ prepared at $T_s\text{=250}$ °C and $\mathrm{P(}{\mathrm{O}}_2{\text{)=3×10}}^{\text{−3}}\hspace{0.17em}\mathrm{Pa}.$ The $\mathrm{Fe}{\text{\hspace{0.05em}2p}}_{\text{3/2}}$ and $\mathrm{Fe}{\text{\hspace{0.05em}2p}}_{\text{1/2}}$ peak profiles for ${\mathrm{Fe}}_3{\mathrm{O}}_4$ layer are little changed by overlaying MgO in the XPS measurements. These results suggest the $\mathrm{Al}/\mathrm{Ag}/{\mathrm{Fe}}_3{\mathrm{O}}_4/\mathrm{MgO}$ multilayers available for spin-dependent tunnel junction.