STATIC AND DYNAMIC PROPERTIES OF MOLECULAR NANOMAGNETS INVESTIGATED BY NMR M.Mariani 1,2, M. Belesi 1, H.Amiri 1, A.Lascialfari 1,2,3, F.Borsa 1, P.Khuntia 1, F. Orsini 2,3, P. Arosio 3, A. Cornia 4, R. Winpenny 5, E. Mc Innes 5, M.Andruh 6, P. Santini 2,7, S. Carretta 2,7, G. Amoretti 2,7 1 Dipartimento di Fisica A.Volta e Unita CNISM, Universita di Pavia, Pavia, Italy 2 S3-CNR-INFM, Modena, Italy 3 DISMAB, Universita` degli studi di Milano, Milano, Italy 4 Dipartimento di Chimica e INSTM, Università di Modena, Modena, Italy 5 Department of Chemistry, University of Manchester, Manchester, UK 6 Inorg. Chemistry Laboratory, University of Bucharest, Bucharest, Romania 7 Dipartimento di Fisica, Università degli studi di Parma, Parma, Italy

The subject Molecular nanomagnets are organic molecules with a limited number of magnetic ions where the intramolecular magnetic interactions are dominant over the intermolecular interaction. IDEAL MODEL SYSTEMS TO INVESTIGATE NANOMAGNETISM We show here three broad classes of nanomagnets showing interesting properties and where NMR has given relevant information

Phonon trapping in Ni10 [1]. The superparamagnetic slowing down of the magnetization in Ni10 nanomagnet is not due to an anisotropy barrier ( as e.g. in Fe8) but rather to a novel phonon trapping phenomenon as demonstrated by the persistence of a narrow proton NMR line even at low T

Heterometallic rings Static effects [2] The redistribution of the local spin density can be probed by 53 Cr NMR in a Cr8 ring where one Cr ion is replaced by a diamagnetic Cd ion

Heterometallic rings Dynamic effects [3,4] The shift in the NMR relaxation rate between the Cr7Fe and Cr7Ni is related to the different perturbation effects of the Fe and Ni ions on the spin dynamics

Single molecule paramagnets [5] The susceptibility is Curie- like down to very low temperature with J =+0.14K in Cu6Fe and J = -1.12K in Cu6Co

Single molecule paramagnets [5] The proton NMR spin-lattice relaxation rate is weakly T dependent down to 4K as in bulk paramagnets

References [1] Belesi et. al, PRL 102,177201(2009) [2] Micoti et al., PRL 97, (2006) [3] H.Amiri et al., umpublished [4] S.Carretta et al,. umpublished [5] P.Khuntia et al,.PRB 80, (2009)