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Tanya Faltens

Index of Example Files?

I'd like to know whether anyone has made a list of the example files (MIF) that lists what features are illustrated in each example.  This would be very useful for figuring out which example files to study, in order to set up a new MIF file to correspond to the user's own system. 

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    Jose Francisco Barron-Lopez

    Hi,

    I've just browsed through the examples featured in this python-based OOMMF calculator. Although MIF files are generated for each example, they are stored in a temporary directory that is not easily accesible for download and they are deleted after each run. Nevertheless, the MIF files can be loaded and read as a text inside the notebooks or stored for late use by modifying the code on the last cell of each example.

    Regarding the content of the Examples, the "First OOMMFC notebook" shows how the problems are defined through python scripts inside this tool. For each example, a system object is created by providing:  material parameters, a mesh with the needed dimensions and a discretization cell, a system Hamiltonian with the relevant energy terms (Exchange, Zeeman, demagnetization...), the dynamic parameters for LLG equation (alpha, gamma) and an initial magnetization configuration. Finally, the system object is allowed to relax and evolve by using the adecuate Driver module.

    The statements for the Micromagnetic Standard Problems are described at the µMAG site at http://www.ctcms.nist.gov/~rdm/mumag.org.html . Problems 1-3 represent magnetic systems under static regime, whereas Problems 4,5 and FMR include dynamic magnetic conditions. All of the Micromagnetic Standard Problems use a Permalloy-like material parameters and, roughly, they illustrate the following situations:

    Micromagnetic standard problem 1: Calculation of the hysteresis M-H loop of a 1 um x 2um x 20nm rectangle of permalloy-like material with an in-plane uniaxial anisotropy.

    Micromagnetic standard problem 3: Calculation of the single domain size limit for a cubic ferromagnetic particle by comparing the energy (E) of its two possible magnetization configurations:  a) the flower or single domain state and b) the vortex or curling state. The energy is obtained as a function of the cube length (L) given in units of the exchange length (lex). The single domain limit (the transition between vortex and flower states) is given by the crossing of the two E vs L curves.

    Micromagnetic standard problem 4: It simulates the time evolution of the magnetization for a thin film (500 nm x 125 nm x 3nm) under the application of two different values of external static magnetic field. At the end, you obtain the plot of the magnetization as a fuction of the time.

    Micromagnetic standard problem 5: It simulates the spin transference torque (STT) phenomena when a spin polarized current (Js) is applied to a permalloy film (100nm x 100nm x10nm) with an initial state of magnetic vortex. At the end of the simulation you can observe the displacement of the vortex centre from its initial position after the application of Js due to the transfered torque.

    FMR standard problem: It simulates the Ferromagnetic Resonance (FMR) spectra in the frequency domain
    of a permalloy thin film (120 nm x 120 nm x 10 nm) under an external applied field by using the "ring down method". First, the film is relaxed under a external magnetic field (Hext) and the initial magnetization (M0) state is obtained. Secondly, a small perturbation is added to move M0 out of equilibrium by changing the direction of Hext. The system is allowed to reach its equilibrium state during the dynamical stage and the time evolution of the magnetization M(t) is recorded. Finally, a Fourier Transform is applyed to the M(t) data then generating the the Power Spectral density signal of the dynamic magnetization, which in turn is proportional to the absorbed microwave power as a function of the microwave frequency during a FMR experiment.  (A detailed description for this problem is given in the reference http://dx.doi.org/10.1016/j.jmmm.2016.08.009 , and all the necesary data, MIF and scripts can be found at https://github.com/fangohr/micromagnetic-standard-problem-ferromagnetic-resonance

    Finally, the notebook "Micromagnetic Model" gives a more detailed description of the mesh, the Hamiltonian, the magnetization, the dynamics and the Drivers used for the simulations.

    Best regards,

    Francisco Barrón-López

     

     

     

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