Regensburg 2007 – wissenschaftliches Programm
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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 15.127: Poster
Dienstag, 27. März 2007, 15:00–19:00, Poster A
Colossal magnetostriction and spin-driven phonon splitting in bond-frustrated Cr-spinels — •Joachim Hemberger, Torsten Rudolf, Christian Kant, Hans-Albrecht Krug von Nidda, Andrei Pimenov, Vladimir Tsurkan, and Alois Loidl — Center for Electronic Correlation and Magnetism, University of Augsburg, D-86135 Augsburg, Germany
The Cr-based cubic spinel compounds ZnCr2X4 (X=S,Se) exhibit complex magnetic ground states which are determined by the competing ferromagnetic (FM) and antiferromagnetic (AFM) exchange interactions yielding strong bond frustration: While in ZnCr2Se4 a spiral AFM structure is established below TN=21 K, in ZnCr2S4 the AFM spiral sets in below TN1=15 K and is changed into a collinear magnetic phase below TN2=8 K. Even though ESR measurements reveal a negligible spin-orbit coupling excluding orbitally induced Jahn-Teller distortions, the observed magnetic transitions are accompanied by significant magnetoelastic anomalies: In both compounds a splitting of individual phonon modes, pronounced thermal expansion anomalies, and large magnetostriction are denoting the spin-driven origin of a structural instability which can be fully suppressed in external magnetic fields. These effects are investigated by means of magnetization, specific heat, thermal expansion, dielectric and IR spectroscopy in external magnetic fields and the results are interpreted in terms of exchange-striction along the competing magnetic bonds.
[1] J. Hemberger et al., Phys. Rev. Lett. 97, 087204 (2006) [2] J. Hemberger et al., cond-mat/0607811