Domain wall formation and spin reorientation in finite-size magnetic systems

We investigate the formation of stable one-dimensional Néel walls in a ferromagnetic slab with finite thickness and finite width. Taking into account the dipolar, the exchange and the uniaxial anisotropic crystalline field interactions, we derive an approximative analytical self-consistent expression that gives the wall width in terms of ratios between the three different energy scales of the problem. We also show that, even when the crystalline anisotropy does not favour the formation of domain walls, they can yet be formed due to the dipolar interaction and the finiteness of the system. Moreover, using a Stoner-Wohlfarth approach, we study the magnetization reorientation inside the domains under the action of an external magnetic field and obtain the respective hysteresis loops, showing that their shapes change from squared to inclined as the width of the slab varies. Finally, we discuss possible applications of this model to describe qualitatively some recent experimental data on thin films of MnAs grown over GaAs substrates.