Magnetization Dynamics in Diluted Magnetic Semiconductor Heterostructures

Doctoral Thesis / Dissertation from the year 2008 in the subject Physics - Theoretical Physics, grade: sehr gut (1,0), University of Dortmund, language: English, abstract: In this thesis spin dynamics in (Zn,Mn)Se/(Zn,Be)Se and (Cd,Mn)Te/(Cd,Mg)Te DMS quantum well heterostructures with a type-I band alignment are studied, where the carriers are quantum confined. Especially the important role of free carriers in heating of the Mn-system, by its interaction with photoexcited carriers with excess kinetic energy, and in the cooling of the Mn-system in the presence of cold background carriers, provided by modulation doping, is established.

The studies are separated in three chapters. In the fourth chapter of this thesis, new results on energy and spin transfer between free carriers and Mn-ion system are presented. Contributions of direct heating of the Mn-system by photocarriers and indirect heating via nonequilibrium phonons are distinguished and their competition is discussed. In the fifth chapter dynamics of spin-lattice relaxation of magnetic Mn-ions in DMS QW heterostructures is investigated and new experimental studies on (Zn,Mn)Se/(Zn,Be)Se heterostructures are shown.

Crucial for spintronic devices is the ability to tune the spin relaxation time precisely, as the spin relaxation time is important in double respects. On the one hand spin polarization must be conserved over long times and distances, if the spin shall be processed or stored in a region, which is spatial separated from the spin-injector. Especially for the possibility of utilizing spins as quantum bits for quantum information processing, long spin polarization is needed. On the other hand short spin relaxation time is needed for fast switching between different spin-states. For instance semiconductor lasers can be switched off extremely fast by reorientation of spin. This very relevant topic is devoted the sixth chapter, before the thesis is summarized in the last chapter. Especially for one of the biggest drawbacks for precise tuning, that the magnetization dynamics in DMS cannot be controlled separately from the static magnetization, solutions via electric field control of the magnetization dynamics or via the technological concept of "digital alloying" are presented.precise tuning, that the magnetization dynamics in DMS cannot be controlled separately from the static magnetization, solutions via electric field control of the magnetization dynamics or via the technological concept of "digital alloying" are presented.