Composites consisting of nonmagnetic particles with sizes in the micro
n range suspended in a ferrofluid constitute an inverse magnetorheolog
ical fluid. Structuring occurs in an applied magnetic field and can re
sult in the solidification of the composite. Above a critical level of
applied stress the material further transforms to a liquid state. Dat
a confirming the existence of a solidified state are presented based o
n constant shear theological measurements. Measurements of the yield s
tress compare favorably with predictions of theory based on the analys
is of unsymmetric stresses in the unyielded, anisotropic medium.