The property [altermagnetism] could boost the storage on computer hard drives, because commercial devices contain ferromagnetic material that is so tightly packed that the material’s external magnetic fields start to see interference – altermagnets could be packed more densely.

I'm not clear on how such a drive would work. Aren't the material's external magnetic fields necessary in order to be able to "read" the data?

https://archive.is/m1qfh