Remanent states and magnetization reversal of nanopatterned spin-valve elements using off-axis electron holography

Remanent states and reversal behavior of nanopatterned spin-valve elements have been investigated using off-axis electron holography and Lorentz microscopy. Arrays of 30-nm -thick CoCuPy (12, 6, and 12 nm, respectively) slotted rings with typical outer diameters ranging from 300 to 600 nm and slot angles of 30°, 60°, and 90° were fabricated by electron-beam lithography. Flux-closure configurations, with zero or one vortex, were the most common remanent states when magnetic fields were applied perpendicular to the slot direction. More complex configurations were introduced for fields parallel to the slot direction. Slotted nanorings with 300100 nm of outer or inner diameter had the most uniform remanent configuration of fully closed flux. Holographic phase images confirmed that the Co and Py layers were coupled in opposite directions at remanence to minimize demagnetization energy. Magnetization reversal processes were investigated: the in-plane switching fields needed to fully reverse both ferromagnetic layers were typically on the order of 600 Oe.