Berlin 2012 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 26: Micromagnetism / Computational Magnetics

MA 26.5: Vortrag

Mittwoch, 28. März 2012, 11:45–12:00, H 0112

Temperature-dependent Heisenberg exchange coupling constants from linking electronic-structure calculations and Monte Carlo simulations — •Danny Böttcher^1,2, Arthur Ernst¹, and Jürgen Henk^1,2 — ¹Max Planck Institute of Microstructure Physics, Halle, Germany — ²Martin Luther University Halle-Wittenberg, Halle, Germany

In various theoretical approximations Heisenberg exchange coupling constants J_ij are calculated for zero temperature and, therefore, provide e.g. too small a critical temperature T_C in comparison to the experimental value. In contrast, J_ij computed within the disordered local moments (DLM) formalism (i. e. for a paramagnetic sample), overestimate T_C. This mismatch leads to the idea of temperature-dependent exchange parameters.

We propose a method to calculate the temperature dependence of J_ij [1]. Within the DLM formalism, the magnetization and the J_ij are computed from first principles for any concentration c of the magnetic constituents. The exchange coupling constants are then used in Monte Carlo (MC) simulations to compute the temperature dependence of the magnetization for the given c. By comparing the magnetization from DLM calculations and from MC simulations we obtain a mapping of temperature versus concentration and eventually temperature-dependent J_ij. The approach which is applied to bulk Fe and Co can for example improve critical exponents.

[1] D. Böttcher, A. Ernst, and J. Henk, J. Magn. Magn. Mat. 324 (2012) 610.