Coercivity Control of Variable-Length Iron Chains in Phthalocyanine Thin Films
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The magnetic characteristics of iron phthalocyanine thin films are studied with a vibrating sample magnetometer, identifying a ferromagnetic transition temperature at 4.5 K. The metal ions at the center of the molecule are self-assembled along chains producing quasi one-dimensional magnetic chains of variable length in the thin films. The average chain length is varied from 20 to 300 nm via substrate temperature during deposition. Below the critical transition temperature, the magnetization curves have the shape of wasp-waisted or constricted loops. The in-plane chain length modulates the coercivity and saturation field and larger grains increase the coercivity significantly. First-order reversal curves of the wasp-waisted hysteresis loops reveal a long narrow strip that suggests a broad distribution of coercive fields and weak intergrain magnetic interactions. These findings are also supported through simulations based on the Preisach model.
KeywordsMetallo-organic molecule Coercivity Low-dimensional ferromagnetism First-order reversal curves Iron chains Preisach model
This work has been supported with by a grant from NSF DMR-0847552 and the support of the College of Natural Sciences and Mathematics at CSU Long Beach. The authors thank José de la Venta and Ivan K. Schuller for performing x-ray diffraction measurement to analyze the film quality at the University of California, San Diego.