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Relatore: Cecilia I. Ventura- Centro Atomico Bariloche and Univ. Nacional de Rio Negro, Bariloche, ARGENTINA.

Aula Fermi
23 Luglio 2010 ore 12.00

One way to probe magnetic order is to measure spin excitations, such as magnons, by inelastic neutron scattering experiments, and compare them with those characteristic of each proposed magnetic phase. Here we will describe our recent studies of magnetic excitations in two families of strongly correlated electron systems. First, for half-doped colossal magnetoresistance manganites, I will report on our study of the spin excitations of the CE phase originally proposed by J. Goodenough. Using a localized spin model we calculated magnons for 3D-perovskite compounds such as La1-xMxMnO3, where M=Ca,Sr,Ba, and for their 2D-laminar counterparts, as e.g. La0.5Sr1.5MnO4 . I will then briefly describe our study for the magnons observed in heavy fermions with antiferromagnetic long-range order (Tneel~TKondo), concretely in CeIn3 and CePd2Si2 single crystals. We used a microscopic model including a lattice of correlated f-electron orbitals (as in Ce,U) hybridized with the conduction band, with competing RKKY (Heisenberg-like JH) and Kondo (JK) couplings.Through a series of unitary transformations, we perturbatively derived a second order effective Hamiltonian which, projected on the antiferromagnetic fermion ground state, describes the spin wave excitations, renormalized by their interaction with the conduction electrons. Our calculated magnon dispersion relations agree well with the experimental data in cubic CeIn3 [M.Acquarone, C.I.Ventura, Journal of Mag. & Magnetic Mats. 321, 2648 (2009)].