Multiturn Counter Using the Movement and Storage of 180$^circ$Magnetic Domain Walls

We describe a novel giant magnetoresistive (GMR) stack geometry which enables the counting of the number of turns of a rotating magnetic field. A race-track-like spiral of N turns acts as a 180deg domain-wall memory. At one end of the spiral, an enlarged film area works as a domain-wall generator. Due to the small width of the spirals themselves in the order of 100-200 nm, there is only domain-wall movement within the spiral. By rotating the magnetic field with/against the sense of the spiral, every half turn increases/decreases the number of domains by one. The number of domain walls have a one-to-one correspondence with the resistance of the spiral due to the GMR effect