Modulating Nanometric Spin Spiral States via Spontaneous Lattice Distortion in a Short Period Helimagnet MnCoSi

We report the influence of spontaneous lattice distortion on the helical spin spiral states in centrosymmetric helimagnet MnCoSi. With the help of in situ Lorentz transmission electron microscopy, we observed significant distortion─up to 57%─in the helical spin order of MnCoSi thin lamella samples. Our analysis, integrating density functional theory calculations with micromagnetic simulations, confirmed that the spontaneous lattice distortion is induced by the variation in the specimen thickness, which therefore modulates the nearest-neighbor exchange interaction J₁ and the next-nearest-neighbor exchange interaction J₂, leading to a change in the spin rotational periodicity. Notably, such a spontaneous lattice distortion can also reduce the critical temperature of the magnetic transition from helix to cycloid. Our findings introduce an additional degree of freedom to effectively tailor the magnetic properties of helimagnets, thereby expanding the possibilities within the emerging field of strain-manipulated spintronics.