Berlin 2005 – wissenschaftliches Programm

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MA: Magnetismus

MA 20: Poster:Schichten(1-29),Spintrsp(30-45),Ex-Bias(46-63),Spindyn(64-75),Mikromat.(76-80),Cluster(81-94),Abbv.(95-99),Obflm(100-02),SpElek.(103-09),E-Theo(110-14),Mikromag.(115-16),Spin+PÜ(117-26),Mag.Mat.(127-51),Meth.(152-55),Mol.Mag(156-59),Kondo(160-65

MA 20.122: Poster

Montag, 7. März 2005, 14:00–18:00, Poster TU C

New model for conversion process in RCu₂ (R = rare earth) — •Sebastian Raasch^1,2, Mathias Doerr¹, Martin Rotter^3,1, Andreas Kreyssig¹, Jens-Uwe Hoffmann², and Michael Loewenhaupt¹ — ¹TUD-IFP, D-01062 Dresden, Zellescher Weg 16 — ²HMI Berlin, D-14109 Berlin — ³Uni Wien-IPC, A-1090 Wien

Since the 1990s a magnetic field induced conversion effect in orthorhombic RCu₂ compounds (space group Imma) has been observed. To force the conversion a strong magnetic field (3 to 20 T) has to be applied in the a-c plane away from the magnetic easy axis. As the magnetization properties of the hard and easy axis exchange during the conversion, this effect has been misleadingly called Ising axis conversion effect based on a metamagnetic transition. Further a giant magnetostrictive effect of more than two percent due to the conversion has been found in 1996 by Takeuchi by macroscopic measurements. We present a new conversion model and its experimental proof: the twin-domain model. It explains the change of the easy axis by structural changes during the conversion. The atoms undergo a slight shift of either 0.29(1) Å or 0.50(1) Å in their atomic positions driven by the external field. Due to the pseudohexagonal structure the crystal decays into many small identical twin-domains of three different orientations. They are rotated along b direction by ± 60.52 deg. Thereby the GMS effect of more than two percent in a direction can be explained. The structural changes due to the conversion have been studied intensely by neutron scattering.