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High-temperature metal–organic magnets

Nature volume 445, pages 291–294 (2007)Cite this article

Abstract

For over two decades there have been intense efforts aimed at the development of alternatives to conventional magnets, particularly materials comprised in part or wholly of molecular components1,2. Such alternatives offer the prospect of realizing magnets fabricated through controlled, low-temperature, solution-based chemistry, as opposed to high-temperature metallurgical routes, and also the possibility of tuning magnetic properties through synthesis. However, examples of magnetically ordered molecular materials at or near room temperature are extremely rare3, and the properties of these materials are often capricious and difficult to reproduce. Here we present a versatile solution-based route to a new class of metal–organic materials exhibiting magnetic order well above room temperature. Reactions of the metal (M) precursor complex bis(1,5-cyclooctadiene)nickel with three different organics A—TCNE (tetracyanoethylene), TCNQ (7,7,8,8-tetracyanoquinodimethane) or DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone)—proceed via electron transfer from nickel to A and lead to materials containing Ni(II) ions and reduced forms of A in a 2:1 Ni:A ratio—that is, opposite to that of conventional (low Curie temperature) MA2-type magnets. These materials also contain oxygen-based species within their architectures. Magnetic characterization of the three compounds reveals spontaneous field-dependent magnetization and hysteresis at room temperature, with ordering temperatures well above ambient. The unusual stoichiometry and striking magnetic properties highlight these three compounds as members of a class of stable magnets that are at the interface between conventional inorganic magnets and genuine molecule-based magnets.

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Figure 1: Temperature dependence of field-cooled (25 Oe) magnetization for 1–3.
Figure 2: Magnetic hysteresis loops for 1 (black line), 2 (blue line), and 3 (red line) at 300 K.
Figure 3: Temperature dependence of the a.c. susceptibility of 3 at different frequencies.

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Acknowledgements

We thank the Natural Sciences and Engineering Research Council of Canada and the University of Victoria for support of this research. We thank F. Palacio (Zaragoza) for assistance with some magnetic measurements and B. Gowen (Victoria) for assistance in scanning TEM and EDX measurements.

Author Contributions R.J. and R.G.H contributed equally to this work. R.J. initiated the work under the supervision of R.G.H. R.J. performed all the syntheses, control experiments, characterization, SEM and EDX measurements of the magnets. K.K. attempted to crystallize these materials, assisted in some control experiments and also processed the magnetic, X-ray photoelectron spectroscopic data. J.B.G. performed some magnetic measurements. K.A.R.M. and K.W. conducted the X-ray photoelectron spectroscopic studies. R.J. and R.G.H. wrote the manuscript. All authors have discussed the results presented and commented on the paper.

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Authors and Affiliations

  1. Department of Chemistry, University of Victoria, PO Box 3065 STN CSC, British Columbia, V8W 3V6, Victoria, Canada

    Rajsapan Jain, Khayrul Kabir, Joe B. Gilroy & Robin G. Hicks

  2. Department of Chemistry, University of British Columbia, British Columbia, V6T 1Z1, Vancouver, Canada

    Keith A. R. Mitchell & Kin-chung Wong

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  1. Rajsapan Jain
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Correspondence to Robin G. Hicks.

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Supplementary Information

This file contains Supplementary Methods; Supplementary Data and Supplementary Figures 1-10 with legends. This file contains descriptions of materials & techniques; compositional analyses data; and spectroscropic data (infrared spectra, 3 figures; solid state electronic spectra, 4 figures; XPS spectra, 6 figures; magnetic data, 13 figures; SEM images, 3 figures; EDX images and spectra, 9 figures; TEM images, 3 figures). (PDF 2229 kb)

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Jain, R., Kabir, K., Gilroy, J. et al. High-temperature metal–organic magnets. Nature 445, 291–294 (2007). https://doi.org/10.1038/nature05439

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