Dresden 2011 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 35: CE: Low-dimensional Systems - Materials 3
TT 35.9: Talk
Wednesday, March 16, 2011, 16:15–16:30, HSZ 301
Helica magnetic structure in the distorted triangular antiferromagnet α-CaCr2O4 — •Sandor Toth1, 2, Bella Lake1, 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 t2g 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 TN=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.