If you’re doing the Exocraft Technician quests, you will reach a point where he sends you out to mine Magnetised Ferrite.
Magnetised Ferrite takes the place of Detritium from 1.3 (you can tell, because in the quest, the name has remained in one instance). Unfortunately, in NEXT, Magnetised Ferrite does not exist as a raw material. If you go looking for Magnetised Ferrite to mine, you will look for ever - there isn’t any.
The only way you can obtain Magnetised Ferrite is to refine it from Pure Ferrite. You can’t mine the stuff.
The quest will happily accept Magnetised Ferrite you have made. It’s not necessary to mine it (even if you could). So don’t be fooled into wasting hours looking for the stuff - there isn’t any. Make it, instead.