Regensburg 2007 – scientific programme

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MA: Fachverband Magnetismus

MA 15: Poster:ThinFilms(1-33),Transp.(34-49),ExchBias(50-56),
Spindynamics(57-70),Micro-nanostr.Mat.(71-82),
Particles/Clust.(83-88), Mag.Imag./Surface(89-96),
Spinelectronics(97-109), Theory/Micromag.(110-116),
Spinstruct/Phasetr.(117-128),Magn.Mat.(129-139),
Aniso.+Measuring(140-145), MolMag.(146-152),
MSMA(153-156)

MA 15.16: Poster

Tuesday, March 27, 2007, 15:00–19:00, Poster A

Thermal spin-wave excitations in GaMnAs — Matthias Sperl, •Ursula Wurstbauer, Werner Wegscheider, Christian Back, and Günther Bayreuther — Institut für Experimentelle und Angewandte Physik, Universität Regensburg, 93040 Regensburg

In conventional ferromagnets thermally excited spin waves determine the temperature dependence of magnetization well below the Curie temperature. The question, whether the distinct exchange interaction between Mn local moments mediated by holes in GaMnAs leads to a different M_S−T relation compared to conventional ferromagnets with direct exchange interaction among 3d electrons, was investigated in this work. GaMnAs samples with thicknesses of 5-200 nm and (2-6%) Mn where grown on GaAs(100) and annealed under different conditions. M(T) was measured with a SQUID (superconduction quantum interference device) magnetometer at temperatures between 2 K and 30 K with regard to thermal spin excitations. It was found that for all samples M_S(T) is in good agreement with Bloch’s law, M_S(T)=M(0)·(1−BT^3/2). Interestingly, the spin wave parameter, B, we found is about two orders of magnitude higher than for Fe or FeCo films. This large difference cannot be understood by a reduced exchange interaction by a reduced Curie temperature alone. However, recent calculations [1,2] indicate that disorder and competing interactions in GaMnAs result in a strong thermal decay of the magnetization and can explain the order of magnitude of B found in the present experiment. [1] A. Singh et. al., cond-mat/0607633 [2] A. Singh et. al., cond-mat/0608474