Ultrathin Co/Pt and Co/Pd superlattice films for MgO-based perpendicular magnetic tunnel junctions

Ultrathin [Co/Pt](n) and [Co/Pd](n) superlattice films consisting of 0.14-0.20-nm-thick Co and Pt(Pd) layers were deposited by sputtering. A large perpendicular magnetic anisotropy [(3-9) x 10(6) ergs/cm(3)] and an ideal square out-of-plane hysteresis loop were attained even for ultrathin superlattice films with a total thickness of 1.2-2.4 nm. The films were stable against annealing up to 370 degrees C. MgO-based perpendicular magnetic tunnel junctions with this superlattice layer as the free layer showed a relatively high magnetoresistance ratio (62%) and an ultralow resistance-area product (3.9 Omega mu m(2)) at room temperature. The use of these films will enable the development of gigabit-scale nonvolatile memory. (C) 2010 American Institute of Physics. [doi:10.1063/1.3524230]