Abstract
We used transmission electron microscopy (TEM) to observe tunable bcc–bct–fcc transformation of FeCo films caused by the addition of auxiliary elements. The crystal structure of the FeCo with added V was bcc, and the transformation of the bcc structure through the bct to fcc was found to depend on the N content (x). TEM observation revealed that bct structure with c/a = 1.12 was obtained for x = 1.7 atomic%, while fcc structure with c/a = 2 was obtained for x = 9.6 atomic%. The c/a-values depended on x, so the bcc–bct–fcc transformation of the FeCoV was tunable by N content. This research was made possible by special preventative measures taken during preparation to avoid compressive stress, which could otherwise induce the bct FeCo lattice of axial ratio c/a > 1.00 to transform to bcc structure. A FeCo coating of thickness 20 nm was therefore deposited directly on a MgO substrate without any other metallic layers.
Highlights
√ was in the range of 1.00 < c/a < 2, where lattice constants (a, c) are based on the bct primitive cell, and the c/a-values of the bcc lattice and the face-centered cubic lattice correspond to 1.00 √
We used transmission electron microscopy (TEM) to observe tunable bcc–bct–fcc transformation of FeCo films caused by the addition of auxiliary elements
TEM observation revealed that bct structure with c/a = 1.12 was obtained for x = 1.7 atomic%
Summary
√ was in the range of 1.00 < c/a < 2, where lattice constants (a, c) are based on the bct primitive cell, and the c/a-values of the bcc lattice and the face-centered cubic (fcc) lattice correspond to 1.00 √. The bct structure can be considered an intermediate structure between bcc and fcc. This relationship is known as the Bain transformation (bcc–bct–fcc), and typically occurs in martensitic materials.. This relationship is known as the Bain transformation (bcc–bct–fcc), and typically occurs in martensitic materials.18,19 By using this method, the bct FeCo structure has been obtained only in ultrathin films less than 5 nm thick because of the lattice relaxation that occurs with increasing film thickness.. FeCo films with elements V and N added were epitaxially grown on a Rh buffer layer, forming bct structure in films thicker than 5 nm. The Rh buffer layer showed the capability to produce the bct FeCo lattice with c/a > 1.00, because √. 1.00 < c/a Rh buffer layer remained to be fully investigated, the effects of the addition of V and N on the formation of the bct FeCo lattice remained unclear
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