Rare-earth-based iron-rich compounds are important industrially in high-performance magnets used in the motors of hybrid and electric vehicles. Following the discovery of Nd-Fe-B magnets there has been intensive pursuit of new permanent magnets based on rare-earth-iron systems. Sm-Fe-N compounds, which are produced mainly as powder, are promising materials because of their higher Curie temperature than Nd-Fe-B magnets. To investigate their magnetic properties and how they have superior characteristics as permanent magnets, single crystals or epitaxial films are necessary.
   We report here the fabrication of epitaxial films of SmFe₇, which is a starting alloy for Sm-Fe-N permanent magnets with TbCu₇-type crystal structure, upon Ta-buffered sapphire substrates. These films were prepared by the RF magnetron sputtering method, using Sm and Fe targets for SmFe₇ films and Ta target for Ta buffer layers. The substrate temperature during film deposition was maintained at 400°C. The thickness of the SmFe₇ and Ta layers were respectively about 40 nm and 360 nm.
   The orientation of the films relative to the substrate was examined by XRD measurements. XRD spectra from 2 theta-omega scanning indicate that SmFe₇ (0001) films and the Ta (111) buffer layer grow normal to the sapphire (0001) substrate surface. Phi scanning measurements show 6-fold symmetry of (11-21) diffraction lines for hexagonal SmFe₇, 3-fold symmetry of (22-2) diffraction lines for cubic Ta, and 3-fold symmetry of (10-14) diffraction lines for rhombohedral sapphire, indicating epitaxial growth of the Ta buffer layer and SmFe₇ film.
   We undertook TEM observations of cross-sections of the films. SmFe₇ grains grew in a columnar manner. Precipitation of α-Fe was found in the film, due presumably to Fe-enhanced deviation from the stoichiometric ratio. An amorphous area in the SmFe₇ film was identified adjacent to the Ta layer. The bottoms of the SmFe₇grains were V-shaped, suggesting that formation of the amorphous area began near the interface and proceeded to form a facet.

1. PRESENTATION: Epitaxial growth of SmFe_{7} films on Ta-buffered sapphire substrate using the RF magnetron sputtering method, PNG image data, 1701 x 980, 8-bit/color RGBA, non-interlaced, 0.1MB

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