Multiscale modelling of magnetic materials
The multiscale scheme proposed in Ref. [1] proceeds as follows. Ab-initio calculations are mapped onto an atomistic spin model based on a classical Heisenberg Hamiltonian. The atomistic model is used to evaluate the temperature dependent parameters anisotropy K(T), saturation magnetisation Ms(T), exchange A(T) and the longitudinal and transverse susceptibilities. These parameters are used for large-scale micromagnetic modelling.
For the parameterisation of the Heisenberg-type model we are using ab-initio modelling based on the SKKR method in collaboration with Prof. L. Szunyogh from Budapest Technical University. Recently we have developed methods to evaluate the temperature-dependent anisotropy, basing on the constrained Monte Carlo method [2] and the temperature-dependent exchange stiffness [3]. At high temperatures our approach uses the Landau-Lifshitz-Bloch dynamical equation of motion [1].
References:
[1] N.Kazantseva, D.Hinzke, U.Nowak, R.W.Chantrell, U.Atxitia and O.Chubykalo-Fesenko “Towards multiscale modelling of magnetic materials: simulations of FePt.”, Phys Rev B 77 (2008) 184428.
[2] P.Asselin, R.F.L.Evans, J.Barker, R.W.Chantrell, R.Yanes, O.Chubykalo-Fesenko, D.Hinzke and U.Nowak “Constrained Monte Carlo method and calculation of the temperature dependence of magnetic anisotropy” Phys.Rev.B 82 (2010) 054415.
[3] U.Atxitia, D.Hinzke, O.Chubykalo-Fesenko, U.Nowak, H.Kachkachi, O.N.Mryasov, R.F.Evans and R.W.Chantrell “Multiscale modelling of magnetic materials: Temperature dependence of exchange stiffness” Phys.Rev.B 82 (2010) 134440.