Electron spin relaxation of N@C60 in CS2

Abstract

We examine the temperature dependence of the electron spin relaxation times of the molecules N @ C 60 and N @ C 70 (which comprise atomic nitrogen trapped within a carbon cage) in liquid C S 2 solution. The results are inconsistent with the fluctuating zero-field splitting (ZFS) mechanism, which is commonly invoked to explain electron spin relaxation for S ⩾ 1 spins in liquidsolution, and is the mechanism postulated in the literature for these systems. Instead, we find an Arrhenius temperature dependence for N @ C 60 , indicating the spin relaxation is driven primarily by an Orbach process. For the asymmetric N @ C 70 molecule, which has a permanent ZFS, we resolve an additional relaxation mechanism caused by the rapid reorientation of its ZFS. We also report the longest coherence time ( T 2 ) ever observed for a molecular electron spin, being 0.25 ms at 170 K .