Dresden 2006 – scientific programme

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MA: Magnetismus

MA 20: Poster: Films(1-36) Transp(37-56) Ex.Bias(57-67) Spindyn(68-80) Micromag(81-95) Particle(96-109) Imag.+Surface(110-113) Spinelectr(114-122) Theory+Micromag(123-131) Spinstr+Aniso(132-142) MagMat(143-156) Meas(157,158) MolMag+Kondo(159-162) Postdead(163-)

MA 20.132: Poster

Tuesday, March 28, 2006, 15:15–19:15, P1

Thermal expansion of multiferroic manganites in magnetic fields — •D. Meier¹, J. Baier¹, O. Heyer¹, J. Hemberger², D. Argyriou³, N. Aliouane³, A. Freimuth¹, and T. Lorenz¹ — ¹II. Physikalisches Institut, University of Cologne, 50937Cologne, Germany — ²Institut für Physik, University of Augsburg, 86159 Augsburg,Germany — ³Hahn-Meitner-Institut, 14109 Berlin, Germany

Strong coupling between magnetic and ferroelectric ordering in some perovskite rare-earth manganites RMnO₃ (R = Gd, Tb) gave rise to intense investigation on these multiferroics. We present high-resolution measurements of thermal expansion and magnetostriction on RMnO₃ (R=Nd, Gd, Tb). NdMnO₃ is a non-multiferroic A-type antiferromagnet (T_N=88K) serving as a reference compound. GdMnO₃ shows antiferromagnetic order for T<T_N=43K. Application of a magnetic field H||b induces an electric polarization P below T ≈ 10K. In contrast, TbMnO₃ shows intrinsic ferroelectricity for T<T_lock=28K already in zero magnetic field. Depending on strength and direction of the magnetic field, P can be suppressed or changes its direction. Our mesurements reveal a huge magnetoelastic coupling, a strong hysteretic behavior and an anisotropic thermal expansion of these compounds. The investigation on the phase boundaries as a function of the magnetic field identifies a new phase transition in TbMnO₃, a bending down of the T_lock-phase boundary in GdMnO₃ for low magnatic fields and a shift of the ferroelectric transition down to lower temperatures in high fields.

This work was supported by the DFG through SFB 608.