Coercivity Dependence on Chain Length in a Low-Dimensional Magnetic System

Single chain magnets deposited in the form of thin films can have tunable average chain lengths. A small molecule, iron phthalocyanine, is sublimed on a non-interacting substrate in the form of a thin film with a thickness of about 100 nm. The molecule's central ions form magnetic chains that are oriented parallel to the substrate surface. Furthermore, the average chain length is varied using the substrate deposition temperature in order to achieve a set of different magnetic responses as measured in magnetic hysteresis loops. The coercivity increases strongly with samples that have longer chain lengths. For comparison, a model with reduced dimensions based on single domain spherical magnetic particles in the superparamagnetic regime is developed and applied to this data set. The lower-dimensionality markedly extends the range of grain sizes over which the coercivity increases.