Each of these layers is made of a pure aluminium layer, plus a high permeability ferromagnetic layer, similar in composition to molybdenum permalloy.
From the en.wikipedia.org
Racetrack memory uses a spin-coherent electric current to move magnetic domains along a nanoscopic permalloy wire about 200 nm across and 100 nm thick.
From the en.wikipedia.org
Unable to escape, trapped electron spins combine and spiral within the permalloy, building into an observable and testable phenomenon called a magnetic vortex core.