Enhanced Spin Ordering and Stability through Chain Alignment in Open-Shell Conjugated Polymer Thin Films

Abstract

Magnetic properties of organic materials have rarely been investigated because of the lack of compatible materials despite its remarkable potential for various applications such as spintronics. Particularly, the relationship between molecular structure and magnetic properties, including magnetization and spin orientation in organic materials, remains unexplored. In this study, a magnetically active open-shell conjugated polymer consisting solely of an open-shell diradical monomer is developed. The bulk polymer shows a typical paramagnetic behavior; however, intriguingly, the polymer films exhibit a ferromagnetic hysteresis loop. Moreover, as the polymer chains are ordered by thermal annealing, a further increase in both saturation magnetization and coercivity is observed. The thermally annealed polymer film exhibits ferromagnetic-like spin ordering at both 10 K and room temperature, as well as high air stability. Furthermore, the magnetic anisotropy depends on the direction of chain alignment and/or backbone orientation in the polymer film. Our findings provide a promising method for designing magnetic polymers and open avenues for spin-based applications utilizing organic materials.