Spin dynamics of antiferromagnetic molecular rings probed by inelastic neutron scattering

Tatiana Guidi, Dipartimento di Fisica ed Ingegneria dei Materiali e del Territorio, Istituto Nazionale Fisica della Materia, Universita' Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, and NCNR

Molecular Nano-Magnets are clusters made of strongly exchange-coupled ions, arranged in regular crystals and forming a macroscopic collection of identical and isolated magnetic units. In this class of systems, magnetic wheels are clusters with a ring-shaped cyclic structure and a dominant antiferromagnetic (AF) coupling between nearest-neighbor ions. For an even number of homo-spin centers, the ground state is a singlet and the excitation spectrum is characterized by rotational and spin-wave like bands. On the contrary, in heterometallic wheels the spin compensation is not fulfilled and the spin ground state can be tailor made choosing the appropriate magnetic ions. I will present the results of Inelastic Neutron Scattering (INS) experiments performed on several ring-shaped molecules for studying the spin correlation and dynamics. Energy and intensity measurements for several intra-multiplet excitation allowed a precise assessment of the zero-field anisotropy, whilst strength and topology of exchange interactions have been determined through measurements of intermultiplet excitations. Quantum effects in AF rings were widely investigated during the past few years. The INS results suggest that heterometallic wheels are good candidates for macroscopic observations of quantum effects.

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