Formation of a Body-Centered Tetragonal Structure With High Magnetic Anisotropy and Coercivity in Fe–Co–V Films With High C Contents

A high amount of C (0–20 at.%) was added to Fe–Co–V films via sputtering to transform their body-centered cubic (bcc) structure to a face-centered cubic (fcc) lattice through a body-centered tetragonal (bct) structure. The Fe–Co films without V retained a bcc or bct crystal structure with an axial ratio (
$c/a)$
of 1.03 even at high C contents close to 20 at.%. Meanwhile, in the Fe–Co films containing 10 at.% of V, a bct structure with
$1.06\le c/a \le1.30$
was formed after adding 5–12 at.% of C, which was subsequently transformed to an fcc structure with increasing C content. The saturation magnetization of the Fe–Co–V–C films with the bct structure was approximately 1000–1500 kA/m, and their uniaxial magnetic anisotropy constant (
$K_{\mathrm {u}}$
) was approximately 106 J/m3 (the films with high Fe contents exhibited high
$K_{\mathrm {u}}$
values). The bct Fe–Co–V–C films with high
$K_{\mathrm {u}}$
were microfabricated into nanodot array patterns via electron beam lithography. The coercivity of the pattern increased with decreasing dot size, and that of the pattern with a dot diameter of 85 nm was nearly an order of magnitude higher than that of the continuous film.