Materials that combine magnetic order with other desirable physical attributes could find transformative applications in spintronics, quantum sensing, low-density magnets and gas separations. Among potential multifunctional magnetic materials, metal-organic frameworks, in particular, bear structures that offer intrinsic porosity, vast chemical and structural programmability, and the tunability of electronic properties. Nevertheless, magnetic order within metal-organic frameworks has generally been limited to low temperatures, owing largely to challenges in creating a strong magnetic exchange. Here we employ the phenomenon of itinerant ferromagnetism to realize magnetic ordering at T C = 225 K in a mixed-valence chromium(II/III) triazolate compound, which represents the highest ferromagnetic ordering temperature yet observed in a metal-organic framework. The itinerant ferromagnetism proceeds through a double-exchange mechanism, which results in a barrierless charge transport below the Curie temperature 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.
Bibliographical noteFunding Information:
This research was supported by the National Science Foundation (NSF) Award no. DMR-1611525, with the exception of the measurement and analysis of the magnetic data, which were supported by the Nanoporous Materials Genome Center of the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences under Award no. DE-FG02-17ER16362. Powder X-ray diffraction data were collected at Beamline 11-BM at the APS, operated by Argonne National Laboratory, and beamline BM31 at the ESRF. We are grateful to our local contact at the ESRF for providing assistance in using beamline BM31. Use of the APS at Argonne National Laboratory was supported by US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract no. DE-AC02-06CH11357. Data from Beamline 11-BM were collected as part of the 2018 Modern Methods in Rietveld Refinement and Structural Analysis workshop, a school supported by the US National Committee for Crystallography and the American Crystallographic Association. Neutron diffraction data were collected at the POWGEN beamline at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Soft X-ray absorption spectroscopy data were collected at Beamline 8.0.1 at the Advanced Light Source of Lawrence Berkeley National Laboratory, a Department of Energy Office of Science User Facility under Contract no. DE-AC02-05CH11231. Electronic structure calculations utilized an award of computer time provided by the ASCR Leadership Computing Challenge (ALCC) program and resources of the National Energy Research Scientific Computing Center, a US Department of Energy Office of Science User Facility operated under Contract no. DE-AC02-05CH11231. Additional computation resources were provided by the Minnesota Supercomputing Institute at the University of Minnesota. T.R. thanks the Welch Foundation (Grant no. N-2012-20190330) for funding. In addition, we thank J. Oktawiec, S. H. Lapidus, X. Wenqian, P. Khalifah, Q. Zhang, M. J. Kirkham, Y.-S. Liu and G. Ren for discussions and experimental assistance, and T.D.H. for editorial assistance. We also thank the National Science Foundation and National GEM Consortium for providing graduate fellowship supports for J.G.P. and B.A.C., respectively.
© 2021, The Author(s), under exclusive licence to Springer Nature Limited.
PubMed: MeSH publication types
- Journal Article