Magnetization tunneling in an enneanuclear manganese cage

The enneanuclear mixed-valent manganese cage [Mn9O7(OAc)(11)(thme)(py)(3)(H2O)(2)] I {Mn-9} possesses an S = 17/2 ground state as a result of an antiferromagnetic interaction between three ferromagnetically coupled Mn-IV ions and a wheel of four Mn-III and two Mn-II ions. AC magnetization measurements show a frequency-dependent out-of-phase signal at 3.4 K and 997 Hz, indicative of single-molecule magnetism behaviour. Data obtained from varying the frequency of oscillation of the AC field gives an effective energy barrier (U-eff) for the reversal of magnetization of 27 K. Magnetic measurements of single crystals of 1 at low temperature show time- and temperature-dependent hysteresis loops which contain steps at regular intervals of field. DC and AC relaxation measurements show both the temperature-dependent and temperature-independent regions, the latter being definitive evidence of magnetization tunneling in the lowest energy zero-field split component of the ground state. (C) 2003 Elsevier Science Ltd. All rights reserved.