Magnetization Dynamics in Rare Earth Doped NiFe and Mn Doped GaAs Films

Magnetization dynamics has been a topic of busy research in the recent years. The dynamical response of magnetic materials to short field pulses is essential for various applications in modern magnetic storage technologies. It is of fundamental interest to acquire a deep understanding of the spin dynamics and intrinsic magnetic relaxation processes in the nano-second time regime. The two key materials parameters which control the response of the magnetic system are the Gilbert damping constant alpha and the magnetic anisotropy field H_a_n_i.

This thesis discusses results on the dynamical response of the Rare Earth doped Ni_8_0Fe_2_0alloys having a thickness of 10 and 30 nm and thin (18 nm), highly doped (Ga,Mn)As films which belong to the class of ferromagnetic semiconductors.

For the characterization of the dynamical properties ferromagnetic resonance (FMR) in the X-band was used. The FMR results which were attained on the temperature dependence of the linewidth measurements provided a clear explanation on the intrinsic damping mechanisms of the magnetization that are present in the investigated samples. The slow-relaxing impurity process was clearly indentified in the Rare Earth doped Ni_8_0Fe_2_0films whereas the low-temperature results on (Ga,Mn)As suggest that the Kambersk 'y torque correlation model is the operating relaxation mechanism in the diluted ferromagnetic semiconductor. The effects of the magnetic anisotropy in (Ga,Mn)As were studied in detail by spatially resolved resonance measurements on rectangular and disk shaped structures.