2. Uniformly magnetized particles

The purpose of this chapter is to show that some dynamical magnetic phenomena which are connected with technological applications, as for example magnetic storage, can be studied with analytical approach. More specifically, the control parameters, namely the quantities that the experimenter can vary at his will, can be found as analytical expression. The only assumption of this approach is that no space dependance of the magnetization vector field $\textbf{{m}}$ is considered. In other words, we suppose to deal with uniformly magnetized particles. In this respect, the first model to explain the hysteretic behavior of suitable uniformly magnetized particles was proposed by Stoner and Wohlfarth in 1948. With this model it is possible to derive equilibrium configurations of magnetization, when the particle is subject to an external field. In the following we will describe briefly the basic ideas of the Stoner-Wohlfarth model, which is a static model as well as Brown's equation presented in the previous chapter. Then, the problem of switching the magnetization in thin-films is analyzed. In this respect, two different magnetization switching processes are presented. For both of them analytical predictions are present in literature, which will be briefly reported. Next, the issue of finding quasi-periodic solutions of LLG equation under circularly polarized field is addressed. This situation commonly arises when typical ferromagnetic resonance experiments are considered. Finally the self-oscillating behavior of LLG equation with spin-transfer torque term is investigated and analytical results regarding critical values of the control parameters are derived. This topic has been recently under the focus of considerable research for its applications to magnetic recording devices and microwave electronics.