New Model Systems for Studying Highly Frustrated Magnetism

Ovidiu Garlea, Ames Laboratory

In the field of frustrated magnetism, the search for new compounds which could provide tests for theoretical predictions or stimulate the development of more elaborate models is rapidly growing. In this respect, I will present recent work on the synthesis and structural determination of Oxygen doped RCuO_2+d, delafossite. The d=0.5 compound represents a first example of the Delta chain, constituted of isolated chains of corner-sharing spin ½ triangles. For d=0.66, the delafossite-type cationic arrangement is modified by oxygen insertion and the copper ions are arranged as an almost regular Kagomé lattice.

In the second part of my talk I will present the results of the first inelastic neutron scattering study of excitations in one of the largest monodispersed magnetic clusters yet investigated, containing thirty Fe⁺³ spins in a frustrated configuration. The large number of s = 5/2 magnetic ions per molecule precludes the diagonalization of the quantum Heisenberg Hamiltonian, and these experimental results provide a stringent test for approximate theories that have been formulated to deal with large finite clusters of interacting spins.

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