  The main-sequence mercury-manganese (HgMn) stars are known to exhibit large
overabundances of exotic elements and, similar to magnetic Ap/Bp stars, are
spectrum variables, implying the presence of an inhomogeneous element
distribution over the stellar surface. A number of magnetic field studies have
been attempted in the last decades, indicating that magnetic fields in HgMn
stars, if they exist, should be rather weak. The presence of tangled magnetic
fields was suggested by several authors who detected quadratic magnetic fields
using the moment technique. We employ the least-squares deconvolution technique
to carry out a sensitive search for weak magnetic fields in spectropolarimetric
observations of three HgMn stars, HD221507, HD65949, and HD101189, which have
different fundamental parameters and spectral characteristics. A definite weak
longitudinal field is discovered in HD221507 and HD65949 on single epochs,
while only marginal field detections were achieved for HD101189. The new
measurements indicate that the structure of the magnetic fields is probably
rather complex: our analysis reveals the presence of reversed Stokes V profiles
at the same observational epoch if individual elements are used in the
measurements. This is the first observational evidence that individual elements
sample distinct local magnetic fields of different polarity across the stellar
surface.
