Micromagnetic simulations of the magnetization dynamics in nanostructures with special applications to spin injection

We present several micromagnetic simulation examples of magnetization dynamics driven by the spin injection. First, we address the validity of the macrospin approximation often used to interpret experimental data. Next, we discuss the interpretation of experimental results obtained on columnar multilayer structures and show that a sophisticated micromagnetic model which takes into account a polycrystalline structure of a nanoelement can explain qualitatively the most important features of the magnetization oscillation spectra observed experimentally. A quantitative agreement with experimental results, however, could not be achieved in the region of reasonable parameter values. The third part of our contribution deals with simulations of the point-contact experiments. Here, we find an important qualitative disagreement between the experiment and simulations. The latter predict the existence of two current regions of a steady-state precession of the point-contact area (before and after spin-polarized current-driven magnetization switching), whereas experimentally only one such region is observed. In conclusion, we discuss some explanations of the above-mentioned discrepancies.