Polarized neutron scattering from model spin-1/2 antiferromagnets

Martin Mourigal (Institut Laue Langevin)

Experimental and theoretical studies of the Heisenberg model have provided deep insights into the role of quantum fluctuations and frustration on the many-body properties of antiferromagnets. Neutron scattering is of crucial importance, allowing a direct benchmarking of theoretical concepts and often revealing unexpected phenomena. In this seminar I will present recent neutron scattering results from two low-dimensional compounds where frustration and quantum fluctuations induce unconventional magnetic ground-states and spin dynamics:

1) In the metal-organic square-lattice material CFTD, anomalous spin excitations are observed at the magnetic zone-boundary and are not captured by conventional spin-wave theory. After a theoretical introduction, I will present polarized neutrons results revealing anomalous lineshapes for the 1- and 2-magnon high-energy responses. These experimental findings will be compared to other cuprates such as La2CuO4 and with recent numerical results from Quantum Monte Carlo. Potential origins for the anomaly will be discussed.

2) The frustrated spin-chain multiferroic LiCuVO4 displays electric polarization simultaneously with spin-spiral magnetic order. I will report a thorough polarized neutron study of its magnetic structure in applied electric and magnetic fields. Relevant mechanisms for ferroelectricity in this edge-sharing cuprate will be discussed based on the determined magnetic structure and on a mean-field analysis.

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Last modified 07-January-2011 by website owner: NCNR (attn: )