  We obtained high-resolution, high signal-to-noise UVES and a few lower
quality HARPS spectra revealing the presence of resolved magnetically split
lines. HD101412 is the first Herbig Ae star for which the rotational Doppler
effect was found to be small in comparison to the magnetic splitting. The
measured mean magnetic field modulus varies from 2.5 to 3.5kG, while the mean
quadratic field was found to vary in the range of 3.5 to 4.8kG. To determine
the period of variations, we used radial velocity, equivalent width, line
width, and line asymmetry measurements of variable spectral lines of several
elements, as well as magnetic field measurements. The most pronounced
variability was detected for spectral lines of He I and the iron peak elements,
whereas the spectral lines of CNO elements are only slightly variable. From
spectral variations and magnetic field measurements we derived a potential
rotation period P_rot=13.86d, which has to be proven in future studies with a
larger number of observations. It is the first time that the presence of
element spots is detected on the surface of a Herbig Ae/Be star. Our previous
study of Herbig Ae stars revealed a trend towards stronger magnetic fields for
younger Herbig Ae stars, confirmed by statistical tests. This is in contrast to
a few other (non-statistical) studies claiming that magnetic Herbig Ae stars
are progenitors of the magnetic Ap stars. New developments in MHD theory show
that the measured magnetic field strengths are compatible with a current-driven
instability of toroidal fields generated by differential rotation in the
stellar interior. This explanation for magnetic intermediate-mass stars could
be an alternative to a frozen-in fossil field.
