Magnetostrictive properties in Fe$_{4-x}$Co$_{x}$N films: Insight from experiments and first-principles calculations

Huameng Yu; Keita Ito; Shoya Sakamoto; Ivan Kurniawan; Yoshio Miura; Yasushi Endo; Takeshi Seki

paper

Magnetostrictive properties in Fe $_{4 - x}$ Co $_{x}$ N films: Insight from experiments and first-principles calculations

arXiv:2609.28864

Abstract

The ferromagnetic nitride Fe $_{4}$ N has attracted attention for application in spintronic devices due to its high spin polarization and large magnetostriction. We present a combined experimental and theoretical study on the magnetostriction of Fe $_{4 - x}$ Co $_{x}$ N films across a wide composition range. The Fe $_{4 - x}$ Co $_{x}$ N films were grown on SrTiO $_{3}$ (001) substrates using molecular beam epitaxy, and the magnetostriction constants along the [100] direction ( $λ$ $_{100}$ ) and [111] direction ( $λ$ $_{111}$ ) were precisely evaluated using an optical cantilever method. The experimental results reveal that $λ$ $_{111}$ remains positive in the whole composition range and shows a maximum value of +82 ppm around x = 0.9. The variation in $λ$ $_{111}$ with x is much smaller than that in $λ$ $_{100}$ , for which giant tunability and sign reversal are observed. First-principles calculations show reasonable agreement with the experimental $λ$ $_{111}$ for x $\geq$ 1.6, but give negative values at lower x, and an exceptionally large negative $λ$ $_{111}$ is obtained at x = 0.8, where the Fermi level coincides with a pronounced minority-spin peak in the density of states. The calculated $λ$ $_{111}$ depends strongly on the smearing parameter, indicating that the rhombohedral magnetostriction is highly sensitive to the treatment of atomic disorder. The saturation magnetostriction constant ( $λ$ $_{s}$ ) derived from $λ$ $_{100}$ and $λ$ $_{111}$ is also compared with the $λ$ $_{s}$ measured for the (001)-oriented polycrystalline Fe $_{4 - x}$ Co $_{x}$ N films, and a possible scenario for deviation between them is discussed. Our findings clarify the basic features of magnetostriction in the Fe $_{4 - x}$ Co $_{x}$ N system, providing essential magnetoelastic parameters for designing nitride-based spintronic devices.

34 pages, 5 figures

Magnetostrictive properties in Fe4−x​Cox​N films: Insight from experiments and first-principles calculations

Abstract

Magnetostrictive properties in Fe $_{4 - x}$ Co $_{x}$ N films: Insight from experiments and first-principles calculations