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Magnetic ordering through itinerant ferromagnetism in a metal–organic framework

Abstract

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 TC = 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.

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Fig. 1: Solid-state structures.
Fig. 2: Spectroscopic characterization.
Fig. 3: Magnetic properties of Cr(tri)2(CF3SO3)0.33.
Fig. 4: Electronic structure calculations and electronic conductivity of Cr(tri)2(CF3SO3)0.33.

Data availability

All data supporting the findings of this study are available within the paper and its Supplementary Information files. Source data are provided with this paper.

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Acknowledgements

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.

Author information

Affiliations

Authors

Contributions

J.G.P. and J.R.L. formulated the project. J.G.P. synthesized the compound. B.A.C. and J.D.G. performed electronic structure calculations and analysed the data. J.G.P. and L.E.D. collected and analysed the magnetic data. M.E.Z. collected X-ray absorption spectroscopy data. J.G.P. and M.L.A. collected and analysed conductivity data. E.V. collected scanning electron microscopy images. H.Z.H.J. collected and analysed the infrared spectra. J.G.P. collected and analysed powder X-ray diffraction data from the APS, with assistance from T.R. M.A.G. collected and analysed powder X-ray diffraction data from the ESRF. M.A.G. and J.G.P. collected and analysed powder neutron diffraction data. J.G.P. and J.R.L. wrote the paper, and all the authors contributed to revising it.

Corresponding author

Correspondence to Jeffrey R. Long.

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The authors declare no competing interests.

Additional information

Peer review information Nature Chemistry thanks Talal Mallah and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Scanning electron microscopy images of Cr(tri)2(CF3SO3)0.33 crystals.

a,b Scanning electron microscopy images of microcrystalline Cr(tri)2(CF3SO3)0.33 powder. Octahedron-shaped crystals have an average edge dimension of ~0.5 μm. Scale bars 2 μm (a) and 1 μm (b).

Extended Data Fig. 2 Analyses of the Cr mixed-valency.

a, N2 adsorption isotherm collected at 77 K for Cr(tri)2(CF3SO3)0.33. Closed and open data points represent adsorption and desorption, respectively. b, Infrared data collected at 150 K (blue) and 300 K (red) and the difference plot (green) for Cr(tri)2(CF3SO3)0.33. Source data

Extended Data Fig. 3 Magnetic data.

a, Variable-temperature magnetic susceptibility data (χM) for Cr(tri)2(CF3SO3)0.33 collected under the applied dc field of 25 Oe. Data plotted as 1/χM versus temperature. Curie-Weiss fit to the data between 300 K and 350 K is shown by a black solid line, with fitting parameters described in the main text. b-f, Variable-temperature in-phase (χ”) and out-of-phase (χ”) ac magnetic susceptibility of Cr(tri)2(CF3SO3)0.33 at selected frequencies of 4 Oe ac oscillating magnetic field and zero dc magnetic field. Source data

Extended Data Fig. 4 Charge analysis.

a, Magnetic moments (µB mol−1) for the ferromagnetic state. b, Atomic charge for the ferromagnetic state in atomic units. c, Magnetic moments (µB mol−1) for the antiferromagnetic state. d, Atomic charge for the antiferromagnetic state in atomic units. Atomic properties shown as a gradient from blue to white to red. Negative magnetic moments indicate spin-down contributions.

Extended Data Fig. 5 Variable temperature conductivity data modeling.

a-d, Variable-temperature log(σ) data of Cr(tri)2(CF3SO3)0.33 plotted versus 1/T0.25 (a), 1/T0.5 (b), and 1/T and fitted with three-dimensional variable-range hopping, Efros-Shklovskii variable-range hopping, and Arrhenius models, respectively (c, d). For clarity, log(σ) versus 1/T plot (c) has been zoomed-in to the intermediate temperature region (d) where conductivity exhibits a weak temperature dependence. Source data

Supplementary information

Supplementary Information

Definition of compound, additional methods, additional discussion, references, Supplementary Tables 1 and 2 and Figs. 1–7.

Supplementary Data 1

Supplementary PXRD Data containing synchrotron powder X-ray diffraction data (.xye) and input (.inp) files used for performing Rietveld refinements in Supplementary Figure 1.

Supplementary Data 2

Supplementary computational data, source data for Supplementary Figure 4.

Source data

Source Data Fig. 2

Statistical source data for Figure 2a,b.

Source Data Fig. 3

Statistical source data for Figure 3a,b,c.

Source Data Fig. 4

Statistical source data for Figure 4e,f.

Source Data Extended Data Fig. 2

Statistical source data for Extended Data Figure 2.

Source Data Extended Data Fig. 3

Statistical source data for Extended Data Figure 3.

Source Data Extended Data Fig. 5

Statistical source data for Extended Data Figure 5.

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Park, J.G., Collins, B.A., Darago, L.E. et al. Magnetic ordering through itinerant ferromagnetism in a metal–organic framework. Nat. Chem. (2021). https://doi.org/10.1038/s41557-021-00666-6

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