By the patterns the neutron make when detected of course.
Different structures will deflect the neutrons in different ways.
I'm afraid you'll have to be more specific.
The magnetic structure types are defined according to how the affect nearby magnetic dipoles right?
So describe the effect ... work out what that means for neutrons.
Google “High Pressure Effects on the Crystal and Magnetic Structure of Pr0.1Sr0.9MnO3 Manganite” N.T. Dang et al. This paper may give you some insight to your questions. They show neutron diffraction spectra of A-type AFM, C-type AFM and G-type AFM along with analysis.