  We investigate the spin-stripe mechanism responsible for the peculiar
nanometer modulation of the incommensurate magnetic order that emerges between
the vector-chiral and the spin-density-wave phase in the frustrated zigzag
spin-1/2 chain compound $\beta$-TeVO$_4$. A combination of magnetic-torque,
neutron-diffraction and spherical-neutron-polarimetry measurements is employed
to determine the complex magnetic structures of all three ordered phases. Based
on these results, we develop a simple phenomenological model, which exposes the
exchange anisotropy as the key ingredient for the spin-stripe formation in
frustrated spin systems.
