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Magnetic Ordering via Itinerant Ferromagnetism in a Metal-Organic Framework

preprint
revised on 26.05.2020 and posted on 28.05.2020 by Jesse Park, Brianna Collins, Lucy Darago, Tomce Runcevski, Michael Aubrey, Henry Z. H. Jiang, Ever Velasquez, Mark Green, Jason Goodpaster, Jeffrey R. Long
Materials that combine magnetic order with other desirable physical attributes offer to revolutionize our energy landscape. Indeed, such materials could find transformative applications in spintronics, quantum sensing, low-density magnets, and gas separations. As a result, efforts to design multifunctional magnetic materials have recently moved beyond traditional solid-state materials to metal–organic solids. Among these, metal–organic frameworks in particular bear structures that offer intrinsic porosity, vast chemical and structural programmability, and tunability of electronic properties. Nevertheless, magnetic order within metal–organic frameworks has generally been limited to low temperatures, owing largely to challenges in creating strong magnetic exchange in extended metal–organic solids. Here, we employ the phenomenon of itinerant ferromagnetism to realize magnetic ordering at TC = 225 K in a mixed-valence chromium(II/III) triazolate compound, representing the highest ferromagnetic ordering temperature yet observed in a metal–organic framework. The itinerant ferromagnetism is shown to proceed via a double-exchange mechanism, the first such observation in any metal–organic material. Critically, this mechanism results in variable-temperature conductivity with barrierless charge transport below TC and a large negative magnetoresistance of 23% at 5 K. These observations suggest applications for double-exchange-based coordination solids in the emergent fields of magnetoelectrics and spintronics. Taken together, the insights gleaned from these results are expected to provide a blueprint for the design and synthesis of porous materials with synergistic high-temperature magnetic and charge transport properties.

Funding

DMR-1611525

DE-FG02-17ER16362

History

Email Address of Submitting Author

gaehyunpark@berkeley.edu

Institution

UC Berkeley

Country

United States

ORCID For Submitting Author

0000-0003-3947-9170

Declaration of Conflict of Interest

The authors declare no competing interests

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