![]() Fe 3O 4 is the ferrimagnetic conducting oxide with spinel crystal structure. In this study, we grew Fe 3O 4 epitaxially on a Si(111) substrate by the insertion of an ultrathin γ-Al 2O 3 buffer layer. However, epitaxial growth of magnetic oxide on Si, which is the most important semiconductor, has not been established because the surface of Si is easily oxidized by the oxygen atmosphere during the evaporation of the magnetic oxides 22. Some research groups fabricated the magnetic oxide on oxide semiconductor, Nb:SrTiO 3, and investigated the transport characteristics including spin transport of the junctions 19, 21. Therefore, the combination of magnetic oxides and semiconductors enables us to produce new functional devices. Recently, NiCo 2O 4 with spinel structure was discovered to exhibit large magnetoresistance effects 20. It is the spinel type ferrimagnetic insulator that is obtained by over oxidation of Fe 3O 4 19. γ-Fe 2O 3 is another candidate as the spin filter barrier. Magnetic oxides possess unique properties 11, 12, 13, 14 Fe 3O 4 or (LaSr)MnO 3 have a half-metallic state, which provides highly spin polarized current 15, and NiFe 2O 4 or CoFe 2O 4 are magnetic insulators, which means that they could work as a spin filter tunnel barrier 16, 17, 18. However, ferromagnetic metals have been used so far because of convenience during fabrication. Magnetic oxides are one of the most promising spin source candidates. The source of the spin current plays an important role in obtaining high-efficiency spin injection. Recently, graphene has also been the subject of spin injection because the spin diffusion length in such light elements is expected to be long owing to small spin–orbit interaction 9, 10. As a result, researchers have succeeded in nonlocal detection 7 or the observation of the Hanle effect 1, which demonstrates the spin state in the semiconductor thus, the behavior of the spin current in the semiconductor can be determined 8. The spin injection technique, in which the spin-polarized currents are injected from ferromagnetic metals into conventional semiconductor materials 2, 3, 6, has been intensely investigated for the preparation of spintronic devices. In particular, the combination of spintronics and semiconductors is a promising technology for the development of the next stage of spintronic devices, e.g., spin-FET or logic devices 4, 5. In the field of spintronics, spin injection and transport phenomena have attracted much attention owing to the possibility of producing novel functional devices 1, 2, 3. The epitaxial Fe 3O 4 layer on Si substrates enable us the integration of highly functional spintoronic devices with Si technology. When Fe 3O 4 was deposited on Si(111) directly, the poly-crystal Fe 3O 4 films were obtained due to SiO x on Si substrate. The Fe 3O 4 films on an amorphous-Al 2O 3 buffer layer grown at room temperature grew uniaxially in the (111) orientation and had a textured structure in the plane. Furthermore, we also found the buffer layer dependence of crystal structure of Fe 3O 4 by X-ray diffraction and high-resolution transmission electron microscope. Both of γ-Al 2O 3 and Fe 3O 4 layer grew epitaxially on Si and the films exhibited the magnetic and electronic properties as same as bulk. To combine oxide spintronics and semiconductor technology, we fabricated Fe 3O 4 films through epitaxial growth on a Si(111) substrate by inserting a γ-Al 2O 3 buffer layer. However, epitaxial spinel ferrite films are generally grown on oxide substrates, not on semiconductors. The epitaxial growth of magnetic oxide on Si could be the first step of new functional spintronics devices with semiconductors. Measured values of the lattice parameter and the thermal expansion coefficient for high‐purity float‐zoned (100 kΩ cm) and Czochralski‐grown (30 Ω cm) single crystals are uniformly distributed within ☑×10 − 5 nm and ☒×10 − 7 K − 1 with respect to the values obtained from the above empirical formula.The application of magnetic oxides in spintronics has recently attracted much attention. It is shown that the lattice parameter in the above temperature range can be calculated using α( t) and the lattice parameter at 273.2 K (0.5430741 nm). ![]() It is found that the temperature dependence of the linear thermal expansion coefficient α( t) is empirically given by α( t)=(3.725 +5.548×10 − 4 t)×10 − 6 (K − 1), where t is the absolute temperature ranging from 120 to 1500 K. Precise measurements are made by the high‐temperature attachment for Bond’s x‐ray method to a few parts per million. The lattice parameter of high‐purity silicon is measured as a function of temperature between 3 K, and the linear thermal expansion coefficient is accurately determined. ![]()
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