  In the celebrated Stern-Gerlach experiment an inhomogeneous static magnetic
field separates a beam of charge-neutral atoms with opposite spins, thereby
driving a ``spin current" normal to the propagation direction. Here we
generalize it to the dynamic scenario by demonstrating a spin transfer between
an AC inhomogeneous magnetic field and intraband electrons or charge-neutral
excitons and phonons. We predict that parametric pumping can efficiently
radiate their DC spin currents from local AC magnetic sources with van der
Waals semiconductors as prototypes. This mechanism brings a unified and
efficient paradigm in the spin transport of distinct mobile carriers.
