Characterization of α-Fe-Free Heteroepitaxial NdFe_12−x Ti _x Thin-Film Materials with a Novel Cubic Laves Fe₂Ti Phase

Thin films with compositions of NdFe₁₂ and NdFe₁₁Ti₁ were fabricated on W-buffered MgO(001) substrates of varying roughness. In this study, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the films microstructurally, chemically, and crystallographically. This study revealed successful heteroepitaxial synthesis of the tetragonal NdFe₁₂ and NdFe_12−x Ti _x phases in the Ti-free and Ti-containing films, respectively, both with surface-normal c-axis orientation. It also revealed the presence of other phases within the magnetic layer. The NdFe₁₂ films contained many α-Fe particles, which preferentially precipitated at locally rough regions of the W-buffer interface. The NdFe₁₁Ti₁ film showed the ubiquitous presence of an Fe₂Ti phase, which covered most of the buffer thereby preventing the formation of α-Fe. This phase was determined to have a novel Cu₂Mg-type cubic Laves (C15) crystal structure with fourfold interfacial symmetry, good coherency, and a low mismatch with the W-buffer, thus rendering itself as being an ideal interface for the heteroepitaxial synthesis of NdFe_12−x Ti _x crystals. It is proposed that successful application of a cubic Fe₂Ti underlayer on W can contribute to the development of a fabrication strategy for NdFe₁₂ thin films without the presence of soft magnetic α-Fe.