FisMat2017 - Submission - View

Abstract's title: SPIN DYNAMICS IN SINGLE ION POLYOXOMETALATE SINGLE-MOLECULE MAGNET [Er(W5O18)2]9-
Submitting author: Manuel Mariani
Affiliation: University of Pavia - Department of Physics
Affiliation Address: Via Bassi 6 27100 Pavia (Italy)
Country: Italy
Oral presentation/Poster (Author's request): Oral presentation
Other authors and affiliations: Ferdinando Borsa (University of Pavia and INSTM, Dept. of Physics, Pavia, Italy, Iowa State University, Dept. of Physics and Astronomy, Ames, Iowa, USA), Michael J. Graf (Boston College, Dept. of Physics, Chestnut Hill, Massachusetts, USA), Samuele Sanna (University of Pavia and INSTM, Dept. of Physics, Pavia, Italy, University of Bologna, Dept. of Physics and Astronomy, Bologna, Italy), Marta Filibian (University of Pavia and INSTM, Dept. of Physics, Pavia, Italy), Tomas Orlando (University of Pavia and INSTM, Dept. of Physics, Pavia, Italy, Max Planck Institute for Biophysical Chemistry, Gottingen, Germany), Sabareesh K. P. Velu (Bilkent University, Dept. of Physics, Çankaya, Ankara, Turkey), Eugenio Coronado (Universitat de Valencia, Instituto de Ciencia Molecular, Paterna, Spain), Alessandro Lascialfari (University of Milano and INSTM, Dept. of Physics, Milano, Italy)
Abstract

In the last twenty years single molecule magnets (SMMs) have been extensively studied for their fascinating quantum properties [1], but also for their possible technological applications [2]. Many systems, consisting in polynuclear complexes formed by magnetic ring of metal ions coupled by exchange interactions, have been synthesized. In recent years a new class of compounds have attracted interest, since the SMMs properties was found also in “double-decker” structures containing only one lanthanide (Ln3+) ion (phthalocyaninatolanthanide complexes [3], Na9[Ln(W5O18)2xH2O [4]). Here we investigated the magnetic properties and spin dynamics of the derivative containing Er3+ ion (ErW10) [4], through NMR and m+SR techniques: with the former we studied, on a powder sample, the 1H absorption spectra, the spin-lattice (T1) and spin-spin (T2) relaxation times at H=3.46, 1.5, 0.43Tesla in the T-range 1.6K<T<300K; with the latter we analyzed the positron asymmetry spectra and the muon relaxation rates lin the range 1K<T<100K in zero-field and at H=500, 2000G longitudinal fields. The spectra present a line-broadening on decreasing temperature (T) indicating a progressive spin freezing of the single molecule magnetic moments, observed also in the structure of the m+SR positron asymmetry spectra. Both techniques yield local fields of the order of 0.3T ascribed to dipolar local fields. On decreasing T, the gradual loss of the 1H NMR signal intensity is observed, due to the so-called wipe-out effect [5] is quantitatively analyzed. T1-1 and λ both show an enhancement as T is lowered. However, while the NMR signal is lost before reaching the very slow fluctuation region, the muon spin-lattice relaxation can be followed to very low T and the characteristic maximum, when the fluctuation frequency becomes of the order of the muon Larmor frequency, can be observed. The data can be reproduced well with a model based on a single correlation time τ = τ0 exp(Δ/T) for the magnetic fluctuations to be compared with previous susceptibility results [4].

 

[1] J. R. Friedman et al.,Phys. Rev. Lett., 1996, 76, 3830; S. Carretta et al., Phys. Rev. Lett., 2007, 98, 167401

[2] F. Troiani et al., Phys. Rev. Lett., 2005, 94, 207208

[3] F. Branzoli et al., J. Am. Chem. Soc., 2009, 131, 4387

[4] M. A. AlDamen et al., Inorg. Chem., 2009, 48, 3467; F. Luis et al., Phys. Rev. B, 2010, 82, 060403R

[5] M. Belesi et al.,  Phys. Rev. B, 2005, 72, 014440