Arrays of magnetized quantum dots at critical conditions

Abstract

Magnetodynamics of an array of ferromagnetically coupled quantum dots are analyzed when accounting for disorder effects, inter- and intra-dot structure. Particular attention is paid for specific features associated with sharp step-like change of a dot magnetic moment caused by the Zeeman splitting of energy levels. For an analysis of the system we employ the randomly jumping interacting moments model including quantum fluctuations due to the discrete level structure, inter-dot coupling and disorder. At the jump anomalies the magnetic state equation is found to indicate an existence of spinodal regions and critical points. In the vicinity of such points magnetization evolves as erratic jumps associated with avalanches of the moment steps in magnetized dots. The model predicts some universal scaling properties for magnetic noise. The considered magnetodynamics is similar to the well-known Barkhausen effect but occurs at conditions far from the magnetization reversal. Such an effect might be employed, therefore, as a tool to analyze the roughness and the disorder in magnetic dot arrays, which are of great importance for advanced electronic devices, nanoscale storage media and magnetic recording technology.