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 \left < B _ { z } \right > , 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 HD 58647 and HD 98922 .
Further , we confirm the previous tentative detection of a weak magnetic field in HD 104237 by Donati et al .
and confirm the previous detection of a magnetic field in the Herbig Ae star HD 190073 .
Surprisingly , the measured longitudinal magnetic field of HD 190073 , \left < B _ { z } \right > = 91 \pm 18 G at a significance level of 5 \sigma is not in agreement with the measurement results of Alecian et al .
( 2013 ) , \left < B _ { z } \right > = -10 \pm 20 G , who applied the LSD method to exactly the same data .
No crossover effect was detected for any star in the sample .
Only for HD 98922 the crossover effect was found to be close to 3 \sigma with a measured value of - 4228 \pm 1443 km s ^ { -1 } G. A quadratic magnetic field of the order of 10 kG was detected in HD 98922 , and of \sim 3.5 kG in HD 104237 .