  The longitudinal resistivity at transitions between integer quantum Hall
states in two-dimensional electrons confined to AlAs quantum wells is found to
depend on the spin orientation of the partially-filled Landau level in which
the Fermi energy resides. The resistivity can be enhanced by an order of
magnitude as the spin orientation of this energy level is aligned with the
majority spin. We discuss possible causes and suggest a new explanation for
spike-like features observed at the edges of quantum Hall minima near Landau
level crossings.
