Epitaxial $\mathrm{Co_2MnSi}$ with intrinsic magnetocrystalline anisotropy as a route to bias-field-free nonlinear half-metal magnonics at the nanoscale
Half-metallic Heusler compounds like $\mathrm{Co_2MnSi}$ allow to bridge magnonic and spintronic functionality for hybrid unconventional computing approaches with sought-after properties like 100% spin polarization and associated low Gilbert damping $α\leq 10^{-3}$. However, the desirable material parameters are inherently tied to the crystal lattice with a particularly critical dependence on structural order in $\mathrm{Co_2MnSi}$. To date, the successful fabrication of nanoscale devices with robust structural integrity remains yet a challenge, and consequently the impact of the material parameters on the resulting nonlinear spin-wave dynamics remains largely unexplored. Here, we report on a study of linear and nonlinear spin-wave dynamics in transversally magnetized $\mathrm{Co_2MnSi}$ waveguides with impeccable crystalline ordering. We show that epitaxial, $\mathrm{L2}_1$-ordered $\mathrm{Co_2MnSi}$ exhibits an intrinsic cubic anisotropy with first- and second-order contributions, stabilizing a magnetization alignment along the crystal $\langle110\rangle$ directions. We confirm the implication of an unaffected crystal structure resulting in preserved magnetic properties in the patterned structures. Herein, the persistent magnetocrystalline anisotropy reshapes the spin-wave dispersion which yields a first-order nonlinear instability suppression range extending over several GHz - even for vanishing bias fields. Moreover, the intrinsic magnetocrystalline anisotropy can be exploited to counteract shape demagnetization for a stabilized low bias field operation in the favourable Damon-Eshbach geometry with high group velocities and decay lengths. Together with the proven half-metallicity and ultralow Gilbert damping, this research establishes $\mathrm{Co_2MnSi}$ as a robust, scalable platform towards bias-field-free nonlinear half-metal magnonics.