Hierarchical structure and the origins of coercivity in exchange-coupled Co-Pt nanochessboards

Abstract We report the first detailed investigation into how exchange-coupled magnetic properties evolve during the formation of the Co-Pt L10 + L12 nanochessboards, which self-assemble by a pseudo-spinodal mechanism below the eutectoid isotherm. The maximum observed coercivities exceed 3 kOe, but these values are more than 5 times lower than the largest values predicted by micromagnetics simulations of ideal, single-colony chessboards. For magnetization reversal controlled by nucleation, a simple analysis readily reconciles this discrepancy by accounting for misorientation associated with the polycrystalline structure that exists at the 50 µm lengthscale, demagnetizing fields associated with eutectoid colonies at the 0.5 µm lengthscale, and non-idealities in the chessboard structure at the tiling lengthscale of about 20 nm.