FUNi posted Haibane Renmei to YouTube, and I am enjoying a rewatch. Every time it happens, I worry that it turns out to be an obsolete anime that only became popular by accident, but no. It is still great. The animation is quite dated, of course, and it was a low-budget production to begin with. There's no HD version. But, still great.

The magical halo is really cute. Note that it's material, so one can, for instance, grab a Haibane by her or his halo. On the other hand, objects easily go between head and halo. At one point, Kuu puts a messenger bag on, and passes the strap under her halo.

Canonically, Haibane realize that there's something fishy going on with their halos. The Lifestyle Diary contains a strip where Rakka sees a novelty item: a tower of levitating magnet rings, and builds analogies with the halo. She does not, however, try to check if magnets disrupt halo's levitation or stick to halo (possibly a good thing).