Regensburg 2007 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 13: Spinstructures and magnetic Phase Transitions
MA 13.9: Vortrag
Dienstag, 27. März 2007, 12:15–12:30, H5
New features in the phase diagram of TbMnO3 — •D. Meier1,2, N. Aliouane3, D. Argyriou3, J. Mydosh1, and T. Lorenz1 — 1II. Physikalisches Institut, University of Cologne, 50937 Cologne, Germany — 2HISKP, University of Bonn, 53115 Bonn, Germany — 3Hahn-Meitner-Institut, 14109 Berlin, Germany
We report new features in the phase diagram of the magnetoelectric (ME) multiferroic TbMnO3, derived by thermal expansion and magnetostriction measurements. Below TN =41 K the Mn spins develop an incommensurate sinusoidal antiferromagnetic ICAFM alignment. Below TFE=28 K, the ICAFM order changes into a helix and a spontaneous electric polarization P||c appears. Sufficiently high magnetic fields H||a or H||b induce a polarization flop (P||c → P||a), accompanied by a commensurate antiferromagnetic (CAFM) order of the Mn spins. Strongly anisotropic thermal expansion was measured along the crystal axes a, b and c (Pbnm). We observe pronounced anomalies when the various phase boundaries are crossed as a function of T or H, reflecting large uniaxial pressure dependencies of the transition temperatures or fields. Thus, our data allow a detailed investigation of the (H,T) phase diagram. Opposite to previous publications, we find that even in high fields there are no direct transitions from the sinusoidal ICAFM- to the CAFM-phase. For H||a, the hysteretic phase boundary between the phases with P||c and P||a was detected in detail for the first time. Furthermore, complex phase boundaries reflecting changes in the Tb ordering for H||i (i=a,b,c) were determined.
This work was supported by the DFG through SFB 608.