Formation and Magnetic Drive of 1D-Confined Topological Defect Lines in Crystals with D$_{2d}$ Symmetry
Designing and controlling topological spin textures within non-collinear magnetic backgrounds is central to the development of low-dissipation spintronic devices. Here we propose a general mechanism based on tunable magnetic anisotropy that enables the realization of one-dimensional topological defect lines embedded within intrinsic spin-spiral states of uniaxial D$_{2d}$-symmetric magnets, and is broadly applicable across diverse material platforms. Using Lorentz transmission electron microscopy and off-axis electron holography, we show that introducing in-plane magnetic anisotropy into the helical ground state stabilizes adjacent domains of conical helices with in-plane propagation vectors, sharing the same handedness but exhibit opposite net magnetization. The resulting interfacial mismatch generates confined bimeron-chains. Significantly, these defect lines are not merely induced merons; their presence is mandated by the specific D$_{2d}$ symmetry constraints inherent to the system. Applying weak magnetic fields along the conical axis drives counter-propagating motion of adjacent bimeron-chains along the helical stripes, while anisotropy-mediated confinement enables track-stable transverse drift free transport. The present work establishes a clear route to stabilize and control topological spin textures within intrinsically non-collinear magnetic states, advancing fundamental understanding and enabling low-dissipation, scalable spintronic device concepts.