Coercivity Dependence on Chain Length in Low-Dimensional Magnetic Systems

Based on their strong optical properties metallo-phthalocyanine thin films have applications in organic photovoltaics and organic light emitting diodes. For specific metal centers, such as iron phthalocyanine (FePc), the metal ion chains form tunable low-dimensional dynamic magnetic systems of fundamental interest. The average chain length can be varied by the deposition temperature in order to achieve a great variety of magnetic hysteresis loops at temperatures below 5 K. The coercivity increases with the chain length in these low-dimensional crystals of finite size. A model with reduced dimensions based on single domain spherical magnetic particles in the superparamagnetic regime is applied and a lower cut-off chain length of around 15 nm is found. The lower-dimensionality markedly extends the range of grain sizes over which the thin film coercivity increases. Fine tuning a model that predicts intrinsic magnetic properties of low-dimensional magnetic chain systems is imperative for optimizing applications.