Magnetically driven molecular orientational ordering in plastic crystals: The case of d-camphor.

This article focuses on the role of magnetic interactions in the orientational order–disorder phase transition of d-camphor, a plastic crystal. Experimental measurements revealed a sharp change in magnetic susceptibility at the transition temperatures (TII–III = 239.8 K on cooling and TIII–II = 245.2 K on warming), indicating long-range antiferromagnetic ordering of the orbital magnetic moments (μMe) generated by the reorientations of methyl groups within the molecules. Additionally, dielectric constant measurements identified two closely spaced discontinuities near the transition, suggesting a complex molecular reorientation process. The findings support a model where the orientational ordering arises from synchronization of molecular magnetic moments to minimize resonant interactions, and the associated entropy changes reflect temporal rather than purely spatial reconfigurations. This approach may extend to understanding similar phase transitions and metastability in other crystalline solids.