Spin dynamics in mesoscopic size magnetic systems: A {sup 1}HNMR study in rings of iron (III) ions

摘要: Two magnetic molecular clusters containing almost coplanar rings of iron (III) ions with spinS=5/2 have been investigated by {sup 1}H NMR and relaxation measurements. The first system, which will be referred to as Fe6, is a molecule general formula [NaFe{sub 6}(OCH{sub 3}){sub 12}(C{sub 17}O{sub 4}H{sub 15}){sub 6}]{sup +}ClO{sub 4}{sup {minus}} {ital or} 15}H{sub 11}O{sub 2}){sub [LiFe{sub while the second type ring, denoted Fe10, corresponds [Fe{sub 10}(OCH{sub 20}(C{sub 2}H{sub 2}O{sub 2}Cl){sub 10}]. linewidth broadened nuclear dipolar interaction coupling protons paramagnetic moment. It found that spin-lattice rate, T{sub 1}{sup {minus}1}, proton sensitive probe Fe spin dynamics. In both clusters, {minus}1} decreases decreasing temperatures from room temperature, goes through peak just below about 30 K in Fe6 10 it drops exponentially very small values at helium temperature. temperature dependence rate discussed terms themore » fluctuations local spins within allowed total configurations framework weak collision theory describe relaxation. We use calculated energy levels for ring based on Heisenberg Hamiltonian value J obtained fit susceptibility semiquantitatively behavior vs T. exponential drop low consistent nonmagnetic singlet ground state separated an gap excited triplet state. (Abstract Truncated)« less