Collective dipolar relaxations in a molecular nanomagnet, Mn12-acetate

Abstract [Mn 12 (CH 3 COO) 16 (H 2 O) 4 O 12 ]·2CH 3 COOH·4H 2 O (Mn 12 -acetate) crystal is a perfect ensemble of identical nanoclusters, with uniform space distribution within the crystal. These tiny magnetic clusters experience dipolar field from one another that potentially result in collective relaxations. We have studied low-temperature, low-field dc magnetic relaxation features of a single crystal of this archetypal single molecular magnet in order to recognize such interactions. The crystal exhibits wait-time dependent memory characteristics of Mn 12 O 12 superspins at 2.85 K, slightly below its blocking temperature. Through time-dependent magnetic measurements, we show that these molecular magnetic clusters undergo collective magnetic relaxation, attributed to the inter-cluster dipolar interactions.