  Our knowledge of the presence and the strength of magnetic fields in
intermediate-mass pre-main-sequence stars remains very poor. We present new
magnetic field measurements in six Herbig Ae/Be stars observed with HARPS in
spectropolarimetric mode. We downloaded from the European Southern Observatory
(ESO) archive the publically available HARPS spectra for six Herbig Ae/Be
stars. Wavelength shifts between right- and left-hand side circularly polarised
spectra were interpreted in terms of a longitudinal magnetic field <B_z>, using
the moment technique introduced by Mathys. The application of the moment
technique to the HARPS spectra allowed us in addition to study the presence of
the crossover effect and quadratic magnetic fields. Our search for longitudinal
magnetic fields resulted in first detections of weak magnetic fields in the
Herbig Ae/Be stars HD58647 and HD98922. Further, we confirm the previous
tentative detection of a weak magnetic field in HD104237 by Donati et al. and
confirm the previous detection of a magnetic field in the Herbig Ae star
HD190073. Surprisingly, the measured longitudinal magnetic field of HD190073,
<B_z>=91+-18G at a significance level of 5sigma is not in agreement with the
measurement results of Alecian et al. (2013), <B_z>=-10+-20G, who applied the
LSD method to exactly the same data. No crossover effect was detected for any
star in the sample. Only for HD98922 the crossover effect was found to be close
to 3sigma with a measured value of -4228+-1443 km/s G. A quadratic magnetic
field of the order of 10kG was detected in HD98922, and of ~3.5kG in HD104237.
