Origin of long-range ferromagnetic ordering in metal–organic frameworks with antiferromagnetic dimeric-Cu(II) building units

• Main Authors: Göettlicher, Jörg, Yi, Jiabao, Li, Sean, Wang, Lan, Ding, Jun, Chen, Banglin, Wei, Su-Huai, Feng, Yuan Ping, Shen, Lei, Yang, Shuo-Wang, Xiang, Shengchang, Liu, Tao, Zhao, Bangchuan, Ng, Man-Fai
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2013
• Online Access: https://hdl.handle.net/10356/97602; http://hdl.handle.net/10220/11263
• Institution: Nanyang Technological University

Even though metal–organic frameworks (MOFs) derived from antiferromagnetic dimeric-Cu(II) building units and nonmagnetic molecular linkers are known to exhibit unexpected ferromagnetic behavior, a comprehensive understanding of the underlying mechanism remains elusive. Using a combined theoretical and experimental approach, here we reveal the origin of the long-range ferromagnetic coupling in a series of MOFs, constructed from antiferromagnetic dimeric-Cu(II) building blocks. Our studies show that the strong localization of copper vacancy states favors spontaneous spin polarization and formation of local moment. These copper vacancy-induced moments are coupled via the itinerant electrons in the conjugated aromatic linkers to establish a long-range ferromagnetic ordering. The proposed mechanism is supported by direct experimental evidence of copper vacancies and the magnetic hysteresis (M-H) loops.