Carrier transport across Fe3O4∕Si interfaces has been studied for two different Si substrate orientations. The Fe3O4 films exhibit a (111) texture on both (111)- and (001)-oriented substrates and field-cooling experiments show the characteristic step in film magnetization at the Verwey transition temperature of magnetite. Current-voltage measurements indicate the formation of high-quality Schottky barriers with an ideality factor of about n=1.06. Fits to the transport data using the thermionic emission/diffusion model yield Schottky barrier heights of 0.52 and 0.65eV for Fe3O4∕Si(111) and Fe3O4∕Si(001) structures, respectively. The interface between the magnetite films and silicon substrates consists of a crystalline iron silicide/amorphous oxide bilayer with reduced magnetic moment.

Carrier transport across Fe 3 O 4 / GaAs interfaces has been studied for n-and p-type GaAs͑001͒ substrates with medium ͑7.7ϫ 10 17 cm −3 ͒ to high ͑3.5ϫ 10 18 cm −3 ͒ carrier concentrations. Currentvoltage ͑I-V͒ measurements on medium-doped substrates show a rectifying behavior that is characteristic for thermionic emission/diffusion across a Schottky barrier. The n-type structure exhibits a low ideality factor of 1.3 and a Schottky barrier height of 0.58-0.63 eV. The Schottky barrier height of the p-type sample is 0.51 eV. For Fe 3 O 4 / GaAs structures with higher doping levels the I -V dependence is nearly symmetric. In this case, tunneling of electrons and holes through the Schottky barrier dominates transport between the Electrical spin injection and detection has been demonstrated between ferromagnetic and normal metals 1 and in semiconductor/͑magnetic͒ semiconductor heterostructures. 2,3 However, one of the main goals of spin electronics, to achieve spin injection from a ferromagnetic metal into a semiconductor, has been more difficult to attain. One particular obstacle is the conductivity mismatch between metals and semiconductors, which drastically limits the spin injection efficiency for ohmic contacts between metals and semiconductors. 4 For nonohmic contacts, however, the conductivity mismatch model of Schmidt et al. does not apply and it has recently been demonstrated that spin injection can be obtained by tunneling through a barrier at the semiconductor interface 5 or by using a magnetic tunnel transistor emitter. 6 An alternative route for spin injection is to use a halfmetallic ferromagnet, which has a completely spin-polarized conduction band, as the spin injector. For perfectly spinpolarized sources, the conductivity mismatch is circumvented even for ohmic contacts, and in the case of tunneling the higher polarization should give a much larger spin accumulation in the semiconductor compared to 3d transition metal injectors. Unfortunately the growth of half-metallic ferromagnets onto semiconductors tends to be more difficult than ferromagnetic transition metals, and very often the spin polarization will be determined more by disordered interfacial layers than by the bulk properties of the ferromagnet itself. Furthermore, perfect spin polarization is a zerotemperature property. The two spin states are mixed, to some extent, at finite temperature. Nonetheless, Fe 3 O 4 has a number of unusual properties that make it attractive as a spinpolarized source.As a class II B half-metal, Fe 3 O 4 is not truly a metal but it is rather a polaronic hopping conductor of minority spins. 7 The resistivity increases with decreasing temperature and goes up sharply at the Verwey transition at about 120 K. 8

The precessional magnetization dynamics of high quality epitaxial magnetite ͑Fe 3 O 4 ͒ thin films growth on MgO are investigated by inductive magnetization dynamic measurements in time and frequency domain. An upper bound for the intrinsic Gilbert damping parameter of ␣ 0 = 0.037Ϯ 0.001 is derived, which is significantly lower than previously reported for epitaxial Fe 3 O 4 on GaAs. With increasing film thickness from 5 up to 100 nm a strong increase in the effective damping up to 0.2 is observed which cannot be explained by simple nonuniform spin wave excitations. Possible origins of this effect are discussed.

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Carrier transport across Fe 3 O 4 / GaAs interfaces has been studied for n-and p-type GaAs͑001͒ substrates with medium ͑7.7ϫ 10 17 cm −3 ͒ to high ͑3.5ϫ 10 18 cm −3 ͒ carrier concentrations. Currentvoltage ͑I-V͒ measurements on medium-doped substrates show a rectifying behavior that is characteristic for thermionic emission/diffusion across a Schottky barrier. The n-type structure exhibits a low ideality factor of 1.3 and a Schottky barrier height of 0.58-0.63 eV. However, one of the main goals of spin electronics, to achieve spin injection from a ferromagnetic metal into a semiconductor, has been more difficult to attain. One particular obstacle is the conductivity mismatch between metals and semiconductors, which drastically limits the spin injection efficiency for ohmic contacts between metals and semiconductors. 4 For nonohmic contacts, however, the conductivity mismatch model of Schmidt et al. does not apply and it has recently been demonstrated that spin injection can be obtained by tunneling through a barrier at the semiconductor interface 5 or by using a magnetic tunnel transistor emitter. 6 An alternative route for spin injection is to use a halfmetallic ferromagnet, which has a completely spin-polarized conduction band, as the spin injector. For perfectly spinpolarized sources, the conductivity mismatch is circumvented even for ohmic contacts, and in the case of tunneling the higher polarization should give a much larger spin accumulation in the semiconductor compared to 3d transition metal injectors. Unfortunately the growth of half-metallic ferromagnets onto semiconductors tends to be more difficult than ferromagnetic transition metals, and very often the spin polarization will be determined more by disordered interfacial layers than by the bulk properties of the ferromagnet itself. Furthermore, perfect spin polarization is a zerotemperature property. The two spin states are mixed, to some extent, at finite temperature. Nonetheless, Fe 3 O 4 has a number of unusual properties that make it attractive as a spinpolarized source.As a class II B half-metal, Fe 3 O 4 is not truly a metal but it is rather a polaronic hopping conductor of minority spins. 7The resistivity increases with decreasing temperature and goes up sharply at the Verwey transition at about 120 K.