Giant Magnetostriction by Design: A First-Principles Screening of Co-based Heusler Alloys

Abstract

The pursuit of high-performance, rare-earth-free magnetostrictive materials is crucial for advancing technologies in sensing, actuation, and microelectromechanical systems. Heusler alloys represent a promising, yet underexplored, class of materials for this purpose. In this work, we perform a systematic first-principles investigation of the magnetostrictive properties of 25 Co-based full Heusler alloys, Co$_2$YZ (Y = V, Cr, Mn, Fe, Co; Z = Al, Ga, Si, Ge, Sn). Our screening identifies 10 compounds with large predicted magnetostriction ($|λ_{001}| > 100$~ppm), highlighted by Co$_3$Si with a giant value of -966~ppm. Furthermore, we demonstrate two effective strategies for engineering magnetostriction: (i) tuning the Fermi level, which enhances the magnetostriction of Co$_3$Sn to -905~ppm via Sb doping, and (ii) amplifying the spin-orbit coupling, which boosts the magnetostriction of Co$_2$CrGa to a colossal -1008~ppm through Re substitution. Our analysis reveals a general predictive rule, uncovering a linear relationship between the magnetostriction and the choice of the Y-site transition metal. This work not only identifies novel candidates for magnetostrictive applications but also establishes clear, physically-grounded design principles to accelerate the discovery of new functional magnetic materials.

Figures (6)

• Figure 1: The L2$_1$ crystal structure of a full Heusler alloy Co$_2$YZ. Blue, purple, and yellow spheres represent the Co, Y (V, Cr, Mn, Fe, Co), and Z (Al, Ga, Si, Ge, Sn) atoms, respectively.
• Figure 2: Enhancement of magnetostriction in Co$_3$Sn via electron doping. (a), (c) Total energy ($E_{\text{tot}}$, open squares) and magnetocrystalline anisotropy energy ($E_{\text{MCA}}$, open triangles) as a function of tetragonal strain for pristine Co$_3$Sn and Sb-doped Co$_3$Sn$_{0.75}$Sb$_{0.25}$, respectively. The inset shows the supercell used for the doped calculation. (b) The rigid band model prediction for the dependence of $E_{\text{MCA}}$ on electron count ($N_e$) for Co$_3$Sn under $\pm$2% strain. (d) The projected density of states (DOS) for Co$_3$Sn (solid line) and Co$_3$Sn$_{0.75}$Sb$_{0.25}$ (dotted-dashed line), The vertical yellow dashed line indicates the Fermi level with Co$_3$Sn as the reference zero. The vertical blue dotted-dashed line represents the shifted Fermi level of Co$_2$Sn$_{0.75}$Sb$_{0.25}$, illustrating the shift of the Fermi level into a DOS peak due to electron doping.
• Figure 3: Enhancement of magnetostriction in Co$_2$CrGa via SOC engineering. $E_{\text{tot}}$ (open squares) and $E_{\text{MCA}}$ (open triangles) versus strain for (a) pristine Co$_2$CrGa and (b) Re-doped Co$_2$Cr$_{0.25}$Re$_{0.75}$Ga. Insets show the respective crystal structures. (c) and (d) illustrate the spatial distribution of the electron localization function (ELF) for Co$_2$CrGa and Co$_2$Cr$_{0.25}$Re$_{0.75}$Ga, respectively, within the Cr-Ga atomic plane. Blue and red regions represent low and high degrees of charge localization, respectively.
• Figure 4: General trends and predictive rules for magnetostriction in Co$_2$YZ (Y = V, Cr, Mn, and Fe) alloys. (a) Correlation between the calculated magnetostriction coefficient ($\lambda_{001}$) and a descriptor combining the density of states at the Fermi level and the square of the Y-site SOC strength, the Co$_2$YSn series is highlighted with blue dots. (b)-(f) Linear relationship observed between $\lambda_{001}$ and the Y-site transition metal for fixed main-group elements Z = Al, Ga, Si, Ge, and Sn, respectively.
• Figure 5: Illustration of the computational design and validation strategy. (a) the compositional factors for tuning magnetostriction in Co-based Heusler alloys, including the choice of Y-site transition metals (with varying SOC strength) and Z-site main group elements (which modulate the electron count). (b) the benchmark calculation performed on Fe$_7$Ga to verify the accuracy of our first-principles approach. Our calculated magnetostriction of 142 ppm for this system is in good agreement with established values.