Local spin dynamics in doped cobalt(II)-radical magnetic chains studied by H-1 NMR

We investigated the spin dynamics of Zn(II)-doped 'single-chain magnet' (SCM) Co(hfac)(2)NITPhOMe (in short CoPhOMe) by means of H-1 NMR measurements. CoPhOMe was the first magnetic chain that showed a slowly relaxing magnetization (commonly called spins' or magnetization 'slowing down' mechanism), which follows the predictions of the Glauber model: the electronic spin freezing sets in before any transition to long-range magnetic order. The slowing down of the magnetization is also evidenced in the Zn-doped samples, which present chains that reach an average length of some tenth of spins for the highest doping, together with growing finite-size effects as the doping concentration is increased. The nuclear spin-lattice relaxation rate T-1(-1) (T) at different applied magnetic fields, displayed a high-temperature peak and a low-temperature shoulder that become lower and shifts toward higher temperatures with increasing the field. This behaviour is qualitatively in agreement with the recent AC susceptibility data that revealed the Glauber dynamics and finite-size effects, like the collective reversal of the spins of each chain segment. (C) 2008 Elsevier B.V. All rights reserved.