Atomic Ordering in Nano-Layered FePt: Multiscale Monte Carlo Simulations
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1177-Z09-03
Atomic Ordering in Nano-Layered FePt: Multiscale Monte Carlo Simulations Rafal Kozubski1, Miroslaw Kozłowski1, Jan Wrobel2, Tomasz Wejrzanowski2, Krzysztof J. Kurzydłowski2, Christine Goyhenex3, Veronique Pierron-Bohnes3, Marcus Rennhofer4, Savko Malinov5 1 Interdisciplinary Centre for Materials Modelling, M. Smoluchowski Institute of Physics, Jagellonian University, Reymonta 4, 30-059 Krakow, Poland 2 Interdisciplinary Centre for Materials Modelling, Faculty of Materials Science and Engineering, Warsaw University of Technology, Warsaw, Poland 3 Institut de Physique et Chimie des Matériaux de Strasbourg, 23, rue du Loess, BP43, 67034 Strasbourg CEDEX 2, France 4 Faculty of Physics, University of Vienna, Vienna, Austria 5 School of Mechanical and Aerospace Engineering, Queen's University, Belfast, UK ABSTRACT Combined nano- and mesoscale simulation of chemical ordering kinetics in nano-layered L10 AB binary system was performed. In the nano- (atomistic) scale Monte Carlo (MC) technique with vacancy mechanism of atomic migration was implemented with diverse system models. The mesoscale microstructure evolution was, in turn, modeled by means of MC procedure simulating antiphase boundary (APB) motion as controlled by APB energies evaluated within the nano-scale simulations. The study addressed FePt thin layers considered as a material for ultra-high density magnetic storage media and revealed metastability of the L10 c-variant superstructure with monoatomic planes parallel to the (001) free surface and off-plane easy magnetization. The layers, initially perfectly ordered in the L10 c-variant, showed homogenous disordering running in parallel with a spontaneous re-orientation of the monoatomic planes into a mosaic-microstructure composed of L10 a- and b-variant domains with (100)- and (010)-type monoatomic planes, respectively. The domains nucleated heterogeneously on the Fe free surface of the layer, grew discontinuously inwards its volume and finally relaxed generating an equilibrium microstructure of the system. Two “atomistic-scale” processes: (i) homogenous disordering and (ii) nucleation of the L10 a- and b-variant domains showed characteristic time scales. The same was observed for the meso-scale processes: (i) heterogeneous L10 variant domain growth and (ii) domain microstructure relaxation. The above phenomena modelled within the present study by means of multiscale MC simulations have recently been observed experimentally in epitaxially deposited thin films of FePt. INTRODUCTION The L10- ordered FePt alloy (Fig.1) due to its high magnetocrystalline anisotropy and an excellent thermal stability of the magnetization direction [1,2], is considered a material for ultrahigh density magnetic storage media. There are several new technologies involving L10 FePt thin layers for improved hard disc drives [3] and a completely new approach for patterned media [4,5]. In terms of technological application, the most interesting are [001]-oriented FePt layers with off-plane easy magnetization resulting from L10 c-
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