We measured mid-infrared polarization of protoplanetary discs to gain new insight into their magnetic fields .
Using CanariCam at the 10.4 m Gran Telescopio Canarias , we detected linear polarization at 8.7 , 10.3 , and 12.5 \micron from discs around eight Herbig Ae/Be stars and one T-Tauri star .
We analyzed polarimetric properties of each object to find out the most likely interpretation of the data .
While the observed mid-infrared polarization from most objects is consistent with polarized emission and/or absorption arising from aligned dust particles , we can not rule out polarization due to dust scattering for a few objects in our sample .
For those objects for which polarization can be explained by polarized emission and/or absorption , we examined how the derived magnetic field structure correlates with the disc position angle and inclination .
We found no preference for a certain type of magnetic field .
Instead , various configurations ( toroidal , poloidal , or complex ) are inferred from the observations .
The detection rate ( 64 per cent ) of polarized mid-infrared emission and/or absorption supports the expectation that magnetic fields and suitable conditions for grain alignment are common in protoplanetary discs around Herbig Ae/Be stars .