Andrey Maljuk

Coupling of frustrated ising spins to the magnetic cycloid in multiferroic TbMnO3

We report on diffraction measurements on multiferroic TbMnO(3) which demonstrate that the Tb- and Mn-magnetic orders are coupled below the ferroelectric transition T(FE) = 28 K. For T<T(FE) the magnetic propagation vectors (tau) for Tb and Mn are locked so that tau(Tb) = tau(Mn), while below T(N)(Tb) = 7 K we find that tau(Tb) and tau(Mn) lock-in to rational values of 3/7b* and 2/7b*, respectively, and obey the relation 3tau(Tb)-tau(Mn)=1. We explain this novel matching of wave vectors within the frustrated anisotropic next-nearest-neighbor Ising model coupled to a periodic external field produced by the Mn-spin order. The tau(Tb)=tau(Mn) behavior is recovered when Tb magnetization is small, while the tau(Tb) = 3/7 regime is stabilized at low temperatures by a peculiar arrangement of domain walls in the ordered state of Ising-like Tb spins.

Ba 2 YIrO 6 : A cubic double perovskite material with Ir 5 + ions

Materials with a 5d4 electronic configuration are generally considered to have a nonmagnetic ground state (J=0). Interestingly, Sr2YIrO6 (Ir5+ having 5d4 electronic configuration) was recently reported to exhibit long-range magnetic order at low temperature and the distorted IrO6 octahedra were discussed to cause the magnetism in this material. Hence, a comparison of structurally distorted Sr2YIrO6 with cubic Ba2YIrO6 may shed light on the source of magnetism in such Ir5+ materials with 5d4 configuration. Besides, Ir5+ materials having 5d4 are also interesting in the context of recently predicted excitonic types of magnetism. Here we report a single-crystal-based analysis of the structural, magnetic, and thermodynamic properties of Ba2YIrO6. We observe that in Ba2YIrO6 for temperatures down to 0.4 K, long-range magnetic order is absent but at the same time correlated magnetic moments are present. We show that these moments are absent in fully relativistic ab initio band-structure calculations; hence, their origin is presently unclear.

Flop of electric polarization driven by the flop of the Mn spin cycloid in multiferroic TbMnO3.

N. Aliouane, 2 K. Schmalzl, D. Senff, A. Maljuk, K. Prokeš, M. Braden, and D. N. Argyriou ∗ Helmholtz-Zentrum Berlin für Materialen und Energy, Glienicker Str. 100, D-14109 Berlin, Germany Institute For Energy, P.O. Box 40, NO-2027 Kjeller, Norway Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, JCNS at ILL, 38042 Grenoble Cedex 9, France II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany (Dated: February 11, 2009)

Iridium double perovskite Sr2YIrO6: A combined structural and specific heat study

Recently, the iridate double perovskite Sr

Diluted paramagnetic impurities in nonmagnetic Ba2YIrO6

_2

Noncollinear antiferromagnetism of coupled spins and pseudospins in the double perovskite La2CuIrO6

YIrO

Unraveling the nature of magnetism of the 5

_6

\boldsymbol{d^4}

has attracted considerable attention due to the report of unexpected magnetism in this Ir

double perovskite Ba

^{5+}

_2

(5d