  We propose a new mechanism for tuning an atomic s-wave scattering length. The
effect is caused by virtual transitions between different Zeeman sublevels via
magnetic dipole-dipole interactions. These transitions give rise to an
effective potential, which, in contrast to standard magnetic interactions, has
an isotropic component and thus affects s-wave collisions. Our numerical
analysis shows that for chromium-50 the scattering length can be modified up to
15 %.
