Toshinori Kajiwara

Room-temperature epitaxial growth of ferromagnetic Fe3Si films on Si(111) by facing target direct-current sputtering

Ferromagnetic Fe3Si thin films with an extremely smooth surface morphology can be epitaxially grown on Si(111) at room temperature by facing target direct-current sputtering. The epitaxial relationship is Fe3Si(111)‖Si(111) with Fe3Si[11¯0]‖Si[1¯10]. By the application of the extinction rule of x-ray diffraction, the generated Fe3Si was confirmed to possess a B2 structure and not a DO3 one. The film showed a saturation magnetization value of 960emu∕cm3, which was slightly lower than that of bulk DO3-Fe3Si. It was observed that the magnetization easy axis was along the [11¯0] direction in the film plane.

Interlayer coupling in ferromagnetic epitaxial Fe3Si∕FeSi2 superlattices

Ferromagnetic epitaxial B2-type Fe3Si∕FeSi2 superlattices were prepared on Si(111) at room temperature by facing target direct-current sputtering. The bilinear and biquadratic coupling constants J1 and J2 of the antiferromagnetically coupled superlattice were comparable to those of the similar superlattices using Fe layers although the saturation magnetization of Fe3Si is approximately half as large as that of Fe. The authors believe that this is due to the formation of a well-ordered quantum well in the spacers, which is mainly caused by the regular accumulation of highly oriented Fe3Si layers.

Epitaxy in Fe3Si/FeSi2 superlattices prepared by facing target direct-current sputtering at room tempertaure

Fe3Si/FeSi2 superlattices were prepared on Si(111) at two deposition rates by facing target direct-current sputtering. For the deposition rates of 2.0 nm/min for Fe3Si and 1.3 nm/min for FeSi2, the Fe3Si layers were nonoriented. On the other hand, for half-deposition rates, the Fe3Si layers were epitaxially grown not only on Si(111) but also up to the top layer across the FeSi2 layers. The antiferromagnetic interlayer coupling between the Fe3Si layers was induced in the epitaxial superlattices, whereas it disappeared in the nonepitaxial superlattices. The regular accumulation of highly oriented Fe3Si layers is crucial for the interlayer coupling induction.

Enhanced Interlayer Coupling and Magnetoresistance Ratio in Fe3Si/FeSi2 Superlattices

[Fe3Si/FeSi2]20 superlattices were prepared on Si(111) at an elevated substrate temperature of 300 °C, and the magnetoresistance ratio and interlayer coupling strengths were enhanced by approximately 100 and 34%, respectively, as compared to those of superlattices deposited at room temperature. While the elevated substrate temperature degraded the interface sharpness, the crystalline orientation and the crystallinity of the Fe3Si layers were apparently enhanced. The latters strongly influence on the interlayer coupling and the magnetoresistance ratio. This implies that quantum well states are tightly formed under the well-ordered crystalline planes, and the spin diffusion lengths are improved due to the enhanced crystallinity.