Molecular-weight dependence of ferromagnetism at room temperature of poly (3-hexylthiophene)

Abstract

Poly (3-hexylthiophene) (P3HT) is one of the promising organic magnetic materials due to its abundant spin properties and excellent solution processing ability. However, the dependence relationship of its magnetic properties on its electronic structure and solid-state order in thin film is unclear. Herein, the effect of molecular weight (Mw) on the ferromagnetism at room temperature of P3HT films was investigated by a comparative study on P3HT with Mw ranging from 19 to 84 kDa. The interference of magnetic impurities was carefully excluded. Structural analyses were performed to investigate the aggregates morphology and molecular features of P3HT thin films with different Mw. Differences in P3HT film ferromagnetism were observed and attributed to variation of solid-state order in mixed solvent. The saturation magnetization (M_s) increases first and then decreases with the increase of Mw, reaching a maximum value of 38.8 emu g⁻¹ at 63 kDa, which was due to the largest molecular chain order and crystallinity of P3HT-63 kDa films. P3HT-84 kDa films had a higher proportion of disordered structural components and limited conjugation length, and yielding low crystallinity and magnetism (10.5 emu g⁻¹).