Abstract
We present a dynamical model that successfully explains the observed time evolution of the magnetization in diluted magnetic semiconductor quantum wells after weak laser excitation. Based on the pseudo-fermion formalism and a second-order many-particle expansion of the exact p–d exchange interaction, our approach goes beyond the usual mean-field approximation. It includes both the sub-picosecond demagnetization dynamics and the slower relaxation processes that restore the initial ferromagnetic order in a nanosecond timescale. In agreement with experimental results, our numerical simulations show that, depending on the value of the initial lattice temperature, a subsequent enhancement of the total magnetization may be observed within the timescale of a few hundred picoseconds.
Highlights
Ultrafast light-induced magnetization dynamics in ferromagnetic films and in diluted magnetic semiconductors (DMS) is today a very active area of research
In III–V ferromagnetic semiconductors such as GaMnAs and InMnAs, a small concentration of Mn ions is randomly substituted by cation sites so that the Mn–Mn spin coupling is mediated by the hole–ion p–d exchange interaction, allowing the generation of a ferromagnetic state with a Curie temperature of the order of 50 K [3]
In the Zener model [5], which was originally developed to describe the magnetism of transition metals, the d shells of the Mn ions are treated as an ensemble of randomly distributed impurities with spin 5/2 surrounded by a hole gas or an electron gas
Summary
Ultrafast light-induced magnetization dynamics in ferromagnetic films and in diluted magnetic semiconductors (DMS) is today a very active area of research. III–Mn–V ferromagnetic semiconductors offer the advantage that they provide a clear distinction between localized Mn impurities and itinerant valence-band hole spins, allowing the basic assumptions of the Zener theory to be satisfied. Based on this hypothesis, a few mean-field models have been successfully applied for modelling the ground-state properties of DMS nanostructures. We derive a dynamical model based on a many-particle expansion of the p–d exchange interaction in the pseudo-fermion framework This formalism, originally developed by Abrikosov [14] to deal with the Kondo problem, introduces unphysical states in the Hilbert space for which impurity sites are allowed to be multiply occupied. In agreement with recent experimental results [9], our simulations show that, depending on the initial lattice temperature, a subsequent enhancement of the total magnetization is observed within the timescale of 100 ps
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
