Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 24: Magnetic Semiconductors

MA 24.13: Vortrag

Mittwoch, 25. März 2009, 18:00–18:15, HSZ 401

Local mapping of anisotropy in individual (Ga,Mn)As micro and nanostructures — •Frank Hoffmann, Georg Woltersdorf, and Christian H. Back — University Regensburg, Germany

(Ga,Mn)As films show a superposition of various magnetic anisotropies which have different physical origins. Recently it was shown that the effective anisotropy can be altered significantly when the film is patterned into nanoscale elements [1]. For spin-injection and magnetotransport experiments with (Ga,Mn)As microstructures the knowledge of the magnetic ground state, the magnetic anisotropies and the switching behavior is crucial. By combining time-resolved Kerr microscopy and ferromagnetic resonance (FMR) we are able to perform local resonance and hysteresis measurements on individual nanostructures. The influence of strain on the magnetic anisotropies was investigated for two sample geometries. We observe a strong strain-relaxation induced uniaxial anisotropy with an easy axis parallel to the long edge for rectangular-shaped structures. Anisotropic relaxation of compressive strain in the (Ga,Mn)As stripes on a GaAs(001) substrate is the underlying mechanism for this behavior. In contrast our experiments on disk-shaped elements with laterally isotropic strain relaxation only show a lowering of the out-of-plane strain-induced anisotropy. These local changes of the magnetic anisotropy which take place at the boundary of the elements can be even imaged with our spatially resolved measurements.

[1] Wenisch et al., PRL 99, 077201 (2007)