Here is presented a set of efficient numerical methods for 3D micromagneticsimulation based on the Landau-Lifchitz-Gilbert equation, making up a code named feeLLGood.The finite element approach was chosen for its geometrical flexibility. The adoptedformulation meets the orthogonality constraint between the magnetization and its time derivative,unlike the over-dissipative classical formulation. A midoint rule was developed forthe Landau-Lifchitz-Gilbert equation which is stable and second order in time. This allowsfor much bigger time steps (typically an order of magnitude) than classical schemes at thesame precision. Computing the nonlocal demagnetizing interaction is a real numerical challenge.Several fast computation techniques are compared. Those selected are novel to thefield : the Fast Multipole Method (FMM) and Non-uniform Fast Fourier Transforms (NFFT).After the code is validated on test cases and its efficiency established, applications to the simulationof nanostructures are presented : chirality selection and ferromagnetic resonanceof a cobalt monovortex dot, Neel caps hysteresis in an iron dot. Finally, the study of a spintronicoscillator proves the code’s upgradability.
