Berlin 2008 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 18: Poster I : Bio Magn. (1-2); Mag.Imgaging (3-9); Magn. Semiconductors (10-16); Half Metals & Oxides (17-20); Coupl.Phenomena (21-27); Magn. Mat. (28-41); Micro & Nanostr. Magn. Materials (42-61); Micro Magn. (62-64); Surface Magnetism (65-70); Transport Phenomena (71-85)

MA 18.38: Poster

Dienstag, 26. Februar 2008, 15:15–18:30, Poster E

Local measurement of magnetic anisotropy in (Ga,Mn)As — •Frank Hoffmann, Matthias Sperl, Georg Woltersdorf, Ursula Wurstbauer, and Christian Back — University Regensburg, Germany

The magnetic properties of the ferromagnetic and semi-conducting material (Ga,Mn)As can be accessed by means of static and dynamic experimental approaches (e.g. SQUID, FMR). In contrast to these integrative methods we present a dynamic approach which combines FMR and Kerr microscopy. This local technique enables us to investigate magnetic anisotropies within the laser spot diameter (submicron resolution). Microwaves in the GHz range which are synchronized to the laser probe pulses are used for the excitation of the magnetization. The magnitude of the precessional motion of the magnetization is measured by means of the magneto-optic Kerr effect. By sweeping the magnetic bias field at a fixed excitation frequency both resonance field and linewidth can be obtained. From the angular dependence of the resonance fields, the anisotropy constants can be determined.

Our results of (Ga,Mn)As on GaAs(001) at low temperatures can be explained by a superposition of several anisotropies: A cubic anisotropy due to the zinc-blende crystal structure, a uniaxial out of plane anisotropy attributed to the compressive strain of (Ga,Mn)As on GaAs and an additional uniaxial in-plane anisotropy in agreement with standard FMR results [1]. At higher temperatures a spin reorientation due to the vanishing of the cubic anisotropy was found.

[1] Liu et al., PRB 67, 205204 (2003)