Reversal and thermal stability of ordered moments in nano-rings of perpendicular anisotropy Co/Pd multilayers

Abstract

Magnetic properties of the ring array made with ultrathin (Pd-/Co-layer thickness ~0.5/0.25 nm) Co/Pd multilayers are reported. Systematic investigation of magnetization loops M(H) at varying temperatures (T = 3–300 K) and magnetic relaxations (at T = 300 K) were carried out in a plain film and ring arrays with different ring widths of 660, 500 and 340 nm. The M(H) loops of all the samples show anisotropy distribution, a reversal mechanism facilitated by nucleation of the reverse domain followed by pinning dependent domain wall motion, and a thermally stable remanant state with Ub/kT  >  250 (at T = 300 K, where Ub is the activation barrier). Both anisotropy distribution and pinning are found to increase in the nanostructures along with a precipitous rise of the reversal field below  ≈100 K. These results are discussed in terms of the presence of chemically sharp/disordered interface regions and inter-layer interactions in the Co/Pd multilayers.