Dresden 2011 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 35: CE: Low-dimensional Systems - Materials 3

TT 35.9: Vortrag

Mittwoch, 16. März 2011, 16:15–16:30, HSZ 301

Helica magnetic structure in the distorted triangular antiferromagnet α-CaCr₂O₄ — •Sandor Toth^{1, 2}, Bella Lake^{1, 2}, Nazmul Islam¹, Simon Kimber³, Oliver Pieper¹, Dimitri Argyriou¹, Manfred Reehuis¹, and Oksana Zaharko⁴ — ¹Helmholt Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany — ²Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany — ³ESRF, 6 Rue Jules Horowitz BP 220, 38043 Grenoble Cedex 9, France — ⁴Laboratory for Neutron Scattering, PSI, CH-5232 Villigen, Switzerland

α-CaCr₂O₄ is a distorted triangular lattice antiferromagnet. The S=3/2 magnetic Cr³⁺ ions are located on slightly distorted stacked triangular layers. The octahedral enviroment ensures that the 3 d-electrons occupy the low lying t_2g levels and that the orbital moment is quenched. Magnetic susceptibility suggests strong magnetic correlations below 50 K. Powder and single crystal neutron diffraction show helical magnetic ordering below T_N=42.6 K, where the ordering wave vector k∼(0 1/3 0) and the angle between neighboring spins within the triangular plane is 120^∘. Spherical neutron polarimetry unambiguously proved that the helical plane is perpendicular to the b axis. The observed magnetic order is a characteristic of nearest neighbor Heisenberg interactions on an equilateral triangular lattice in apparent contradiction to the distorted crystal which allows for 4 inequivalent nearest neighbour exchange paths. By simulating the magnetic order of α-CaCr₂O₄ as a function of these 4 interactions it is found that 120^∘ helical order is in fact stable over a large range of parameter space.