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OOMMF-temperature

OOMMF input parameter files (MIF) to include temperature in micromagnetc simulations with the Object Oriented Micromagnetic Framework.

OOMMF can be found under https://math.nist.gov/oommf/

To simulate the movement of the macroscopic magnetic moment in ferromagnetic systems under the influence of elevated temperatures, the stochastic version of the Landau-Lifshitz (LL) or the Landau-Lifshitz-Gilbert equation with a spin density of one per unit cell can used. To apply the stochastic LL to micromagnetic simulations, where the spin density per unit cell is generally higher, a conversion has to be performed. Details can be found in the literature[1]. Briefly: To determine the scaling between the physical temperature (T_eff ) and the input parameter used as simulation temperature (T_sim ) the lattice constant (a_eff ) and the length of a elementary simulation cell (a_sim ) has to be set into relation. The temperature T_sim as used in the simulation as input parameter can be determined from the physical temperature T_eff by:

T_sim = (a_sim / a_eff) * T_eff

The range where scaling can be applied one has to consider the temperature effects on the exchange length of the system.1 Cell sizes of 1-2 nm in combination with time steps around 1 fs are a reasonable starting points. Sample files for OMMF are attached. These files can be used to determine the Curie temperature for the classical bulk magnets, iron, nickel and cobalt.

Reference:

[1] Hahn, M. B. , Journal of Physics Communications 3, 075009 (2019). DOI: 10.1088/2399-6528/ab31e6

Temperature in micromagnetism: Cell size and scaling effects of the stochastic Landau–Lifshitz equation.

https://doi.org/10.1088/2399-6528/ab31e6