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    Atomistic modeling of magnetization reversal modes in L10 FePt nanodots with magnetically soft edges

    Jung-Wei Liao1,2, Unai Atxitia2,3,*, Richard F. L. Evans2,†, Roy W. Chantrell2, and Chih-Huang Lai1,‡

    • 1Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
    • 2Department of Physics, The University of York, York YO10 5DD, United Kingdom
    • 3Departamento de Fisica de Materiales, Universidad del Pais Vasco, UPV/EHU, ES-20018 San Sebastian, Spain
    • *Present address: Department of Physics, University of Konstanz, Konstanz D-78457, Germany.
    • richard.evans@york.ac.uk
    • chlai@mx.nthu.edu.tw

    Phys. Rev. B 90, 174415 – Published 13 November, 2014

    DOI: https://doi.org/10.1103/PhysRevB.90.174415

    Abstract

    Nanopatterned FePt nanodots often exhibit low coercivity and a broad switching field distribution, which could arise due to edge damage during the patterning process causing a reduction in the L10 ordering required for a high magnetocrystalline anisotropy. Using an atomistic spin model, we study the magnetization reversal behavior of L10 FePt nanodots with soft magnetic edges. We show that reversal is initiated by nucleation for the whole range of edge widths studied. For narrow soft edges the individual nucleation events dominate reversal; for wider edges, multiple nucleation at the edge creates a circular domain wall at the interface which precedes complete reversal. Our simulations compare well with available analytical theories. The increased edge width further reduces and saturates the required nucleation field. The nucleation field and the activation volume manipulate the thermally induced switching field distribution. By control of the properties of dot edges using proper patterning methods, it should be possible to realize exchange spring bit-patterned media without additional soft layers.

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