Stress Micromagnetics Of Ferromagnetic Thin Film Unit

In recent years, with the development of the computing ability of computer, micromagnetic simulation method has become one important tool to study the ferromagnetic materials especially ferromagnetic thin film materials in the magnetism field. The distributions of the magnetic moments, domain switching and domain walls rotation can be studied by micromagnetic simulating. Thus the relationship between the macroscopic properties of ferromagnetic materials and their microstructure parameters can be obtained. Micromagnetic simulation has already been an important tool for studying the magnetization and reverse magnetization mechanism of ferromagnetic materials in micron scale.In the thesis, the energies including external magnetic energy, exchange energy, demagnetizing field energy, anisotropy energy and magnetoelastic energy were analyzed in detail. To obtain the formulas of the discretization energies, Finite Difference Method was utilized. To reduce the computation cost of calculation of the demagnetizing field Fast Fourier Transform algorithm was designed.Then, conjugate gradient algorithm and Euler algorithm have been constructed according to the energy minimization theory and solving the LLG equation respectively. On this basis, micromagnetic simulating codes have been developed in the VC++ environment.Finally, the stress-dependence of the magnetic properties and the domains of the 200nm×200nm×5nm ferromagnetic film cell on the applied field have been studied with the micromagnetic codes. The results show that the shapes of hysteresis loops, coercivity and remanence changed in some regularity with the difference applied stress. With the increase of tensile stress which is parallel to the direction of the external magnetic field, both of the coercivity and the remanence increase. While with the increase of compressive stress, both of the coercivity and the remanence decrease. The variations of the magnetic properties with applied stress are result from the stress-induced anisotropy. The domain rotating patterns under tensile and compressive stress are similar, both beginning with the anti-magnetization nucleation formed at the four corners. With the increase of the reverse magnetic field, the domain structure with a shape of"C"was formed, and the domains reverse finished finally. With the further increase of the reverse magnetic field, compared to tensile stress, domain reverse finished at a lower magnetic field when under compressive stress.