Magnetotactic bacteria (MB)-cocci as well as a spirillum of type Magne
tospirillum gryphiswaldense-were investigated for their applicability
for nondestructive domain analysis on soft magnetic materials. Solely
magnetotactic cocci which show a definite swimming direction proved to
be suitable for this purpose. The intensity of the domains' magnetic
stray field H of coated SiFe sheets proved to be high enough to visual
ize main domains even in distances of 500 mum from the specimen surfac
e, in comparison to about 5 mum for colloid particles. Thus it was pos
sible to develop a specific ''domain viewer'' which allows simple hand
ling and reuse of bacteria for repeated analysis. Based on theoretical
considerations about the cocci's motion in a magnetic field, a comput
er program for the simulation of spatiotemporal bacteria distributions
was developed. Results show that-in contrast to colloid techniques an
d nonmotile bacteria-the gradient of H does not influence the contrast
in an essential way. Due to Brownian motion of motile bacteria, a min
imum domain width is required for effective visualizations. This was c
onfirmed by experimental results of both secondary domains of crystall
ine specimens and narrow surface domains of amorphous bands. However,
for small domain structures of the latter, unmotile dead bacteria prov
ed to be applicable. Finally, influences of bacteria concentrations on
the contrast as well as the contrast mechanism as a function of time
are discussed.