The L1₀ systems are extensively studied as good candidates for high density magnetic storage media due to their high magnetic anisotropy, which is related to their chemical order anisotropy. In recent experiments, epitaxied thin bilayers NiPt/FePt/MgO(001) grown at 700K were annealed at 800K and 900K. At 800K, the L1₀ long range order increases without measurable interdiffusion. Surprisingly further annealing at 900K leads to interdiffusion that takes place without destroying the L1₀ long range order [1]. The same phenomenon has been observed by Rennhofer et al. [2] in the case of L1₀ FePt multilayers suggesting that interdiffusion can occur through a series of atomic mechanisms while keeping the L1₀ structure. As this point is important for the growth of high quality layers of alloys, we have investigated the possible atomic processes through numerical simulations for such diffusion without order change. We have used Molecular Dynamics in the second moment approximation of the tight binding method taking as reference CoPt that orders in the L1₀ tetragonal structure like FePt and NiPt. In a first stage, molecular statics calculations were performed in order to study the vacancy migration and to determine in particular if some jump cycles are feasible with an energy barrier low enough to make possible a diffusion without order change. For instance we find that a 6 jump cycle mechanism is favourable from an energy point of view relatively to a second nearest neighbour jump that has a much higher energy barrier. We have also checked mechanisms involving two or three vacancies. The static results are supported by a statistical study for which large series of constant energy simulations are performed at the temperatures of interest (900-1000 K) in order to check the actual occurrence of each elementary step of the previously identified jump cycles.

[1] R. V. Montsouka et al., Phys. Rev. B 74, 144409 (2006)
[2] M. Rennhofer et al., Phys. Rev. B 74, 104301 (2006)

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/15954 must be provided.

1. Quenched molecular dynamics simulations of the vacancy behaviour near the (001) surface of an ordered CoPt alloy
2. Surface effect on atomic ordering in nano-layered L1₀ AB binaries: multiscale Monte Carlo Simulation
3. Formation of stacking defects at surfaces: From atomistic modelling to DFT calculations.
4. Comparison of patterning of highly ordered CoPt alloys with perpendicular anisotropy using two methods: ion etching and ion irradiation
5. Interdiffusion of two L1₀ phases without order decrease : experiments and molecular dynamics simulations
6. ATOMIC MIGRATION ON ORDERING IN BULK AND NANOSTRUCTURED FePt L10-ORDERED INTERMETALLIC COMPOUND SHOWING HIGH MAGNETIC ANISOTROPY.
7. ATOMISTIC MODELLING OF SUPERSTRUCTURE REFINEMENT IN CRYSTALLINE MATERIALS