Above a critical shear rate we observe in suspensions polarized by an exter
nal field an abrupt jump of stress and the onset of a layered stripe patter
n. This novel shear-induced transition can be systematically found by using
appropriated geometry. We show that it can be explained by the transition
from a nematiclike order induced by the field to anisotropic state which is
obtained when the shearing hydrodynamic forces on a pair of particles over
come the magnetic or electrostatic forces. The critical shear stress predic
ted on this basis is in good agreement with the experimental results. [S003
1-9007(98)08119-8].