Spin Symmetry Breaking: Superparamagnetic and Spin Glass-Like Behavior Observed in Rod-Like Liquid Crystalline Organic Compounds Contacting Nitroxide Radical Spins

Symmetry

Shuichi Sato¹  Yoshiaki Uchida²  Rui Tamura³ 

[1] Department of Physics, Osaka Dental University, Hirakata, Osaka 573-1121, Japan;Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan;Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan;

关键词: spin symmetry breaking;    magnetic liquid crystals;    magneto-LC effect;    nitroxide radicals;    superparamagnetic domain;    spin glass state;   

DOI  :  10.3390/sym12111910

来源: DOAJ

【 摘 要 】

Liquid crystalline (LC) organic radicals were expected to show a novel non-linear magnetic response to external magnetic and electric fields due to their coherent collective molecular motion. We have found that a series of chiral and achiral all-organic LC radicals having one or two five-membered cyclic nitroxide radical (PROXYL) units in the core position and, thereby, with a negative dielectric anisotropy exhibit spin glass (SG)-like superparamagnetic features, such as a magnetic hysteresis (referred to as ‘positive magneto-LC effect’), and thermal and impurity effects during a heating and cooling cycle in weak magnetic fields. Furthermore, for the first time, a nonlinear magneto-electric (ME) effect has been detected with respect to one of the LC radicals showing a ferroelectric (chiral Smectic C) phase. The mechanism of the positive magneto-LC effect is proposed and discussed by comparison of our experimental results with the well-known magnetic properties of SG materials and on the basis of the experimental results of a nonlinear ME effect. A recent theoretical study by means of molecular dynamic simulation and density functional theory calculations suggesting the high possibility of conservation of the memory of spin-spin interactions between magnetic moments owing to the ceaseless molecular contacts in the LC and isotropic states is briefly mentioned as well.

【 授权许可】

Unknown