  A pure spin current is predicted to occur when an external magnetic field and
a linearly inhomogeneous spin-only field are appropriately aligned. Under these
conditions (such as originate from nuclear contact hyperfine fields that do not
affect orbital motion) a linear, spin-dependent dispersion for free electrons
emerges from the Landau Hamiltonian. The result is that spins of opposite
orientation flow in opposite directions giving rise to a pure spin current. A
classical model of the spin and charge dynamics reveals intuitive aspects of
the full quantum mechanical solution. We propose optical orientation or
electrical polarization experiments to demonstrate this outcome.
