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MA: Magnetismus

MA 4: Magnetic Materials I

MA 4.8: Vortrag

Montag, 27. März 2006, 12:00–12:15, HSZ 401

Magnetic shape memory effect in the paramagnetic state of RCu₂ (R = rare earth) — •Sebastian Raasch¹, Mathias Doerr¹, Andreas Kreyssig¹, Michael Loewenhaupt¹, Martin Rotter², and Jens-Uwe Hoffmann³ — ¹Germany, Technische Universität Dresden, Institut für Festkörperphysik — ²Austria, University of Vienna, Institute for Chemistry — ³Germany, Hahn-Meitner-Institut Berlin

We like to present RCu₂ (R = rare earth) as the first magnetic shape memory (msm) alloy with the magnetic anisotropy of rare earth ions as impelling force. Besides La_2−xSr_xCuO₄ RCu₂ is the second known antiferromagnetic msm-compound class. However, magnetic order is not necessary for the msm effect here. Microstructural changes are possible even above magnetic ordering temperature because the magnetic anisotropy is effective also in the paramagnetic state. RCu₂ compounds have a pseudohexagonal orthorhombic structure which leads to the fact of three twin variants, each rotated about 60 deg to the others along the pseudohexagonal b axis. To our knowledge RCu₂ compounds exist exclusively in the martensitic pseudohexagonal state. To move the twin boundaries, a magnetic field of about 3.2 T and a temperature of typical 30 K is necessary. This moving of twin boundaries correlates with magnetostriction measurements, showing a typical length change of two percent. Depending on the field direction a certain twin variant is favored. We will present neutron data from Tb_0.5Dy_0.5Cu₂ confirming a change of the volume fraction of the three twin-variants. The combination of rare earth magnetizm with the msm effect defines a promising field of science.