Experimental evidence of the dependence of spin tunneling on the concentration of dislocations in Mn12 crystals

We present experimental results on the influence of the concentration of dislocations on resonant spin tunneling in a thermally treated single crystal of Mn-12-2Cl benzoate. The time evolution of the magnetization follows a stretched exponential law over a few time decades for all concentrations. The experimental values for the parameters entering this law were used to derive the thermal-dependent concentration of dislocations. We propose a new scaling term to account for the thermally assisted resonant tunneling at finite temperatures. (C) 2003 Elsevier B.V. All rights reserved.