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Identifier

000376422

Title

Ultrafast control of the magnetic memory of (Ga,Mn)As ferromagnetic semiconductors by femtosecond optical pulses

Alternative Title

Υπερταχύς έλεγχος της μαγνητικής μνήμης σε (Ga, Mn)As σιδηρομαγνητικούς ημιαγωγούς με σύμφωνους οπτικά παλμούς

Author

Λίγγος, Παναγιώτης

Thesis advisor

Περάκης, Ηλίας

Abstract

In this thesis we develop a theory of the collective spin dynamics triggered by ultrafast optical excitation of (Ga,Mn)As ferromagnetic semiconductor and we demonstrate non-thermal control of the magnetization switchings between four metastable magnetic states of (Ga,Mn)As using sequences of linearly polarized optical pulses. Using a tight-binding calculation of the bands, within the mean-field approximation we derive the density matrix equations of motion of carrier populations and coherences including magnetic anisotropy and carrier relaxation effects. We demonstrate the development of a light-induced magnetization tilt during a time interval of a few hundreds of femtoseconds which is governed by the interband nonlinear optical polarizations. This magnetization dynamics is followed by a second temporal regime (picosecond time scale) governed by the magnetic anisotropy of the Fermi sea. Within the mean-field approximation, the dynamics of the collective spin is described by a Landau-Gilbert-like equation for the collective spin. In this theoretical treatment, we propose protocols for multiple switchings using sequences of multiple optical pulses to selectively control the Mn collective spin between the four metastable states depending on the polarization, sequence, phase and the photon energy of the optical pulses.

Language

English

Subject

Magnetic semiconductors

Magneto- optics

Μαγνητικοί ημιαγωγοί

Issue date

2012-11-16

Collection

School/Department--School of Sciences and Engineering--Department of Physics--Post-graduate theses

Type of Work--Post-graduate theses

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