I did my PhD in this area. It’s very difficult to “read” information stored when there is no net magnetism. Hard drives are built using a read head that detects

I did my PhD in this area. It’s very difficult to “read” information stored when there is no net magnetism. Hard drives are built using a read head that detects the stray field from ferromagnetic materials. When there are particular topological textures like skyrmions you do get a spin hall effect which is quantised but in applying currents you also change the magnetisation through something called spin transfer torque.