When Metal Organic Frameworks Turn into One-Dimensional Magnets

Simulations and experiments reveal one-dimensional nano-size magnets are formed in a common porous material.

Image courtesy of Timo Thonhauser
Front view of metal organic framework (MOF-74), showing the almost perfectly one-dimensional chains of transition metal magnets (green sections of structure).

The Science

Simulations in concert with experiments reveal that one-dimensional nano-size magnets are formed in a common model porous material, referred to as MOF-74.  Metal organic frameworks (MOFs) are compounds that consist of metal ions or clusters linked by rigid organic molecules to form one-, two-, or three-dimensional porous structures.

The Impact

This well studied MOF-74 has now been shown to display one-dimensional magnetism, an important first step towards understanding and studying the fundamentals of magnetism. This family of easily synthesized, and potentially inexpensive, one-dimensional magnetic materials could be useful in future magnetic device applications.

Summary

One-dimensional magnets have been discovered in a class of nano-porous material, called MOF-74, by combining advanced simulations with experimental characterization. Metal organic frameworks, or MOFs, contain metal ions and rigid organic molecules.  MOF-74 is a well characterized, model system that is easily synthesized and tailored with different metal atom additions or organic ligands. This compound also displays regular, almost perfect, one-dimensional chains of metal atoms, which are well separated, thus representing an ideal model system. Computer simulations were performed on MOF-74 with different metals at the corners, including Fe, Co or Ni, and showed that an interaction leading to significant magnetism occurs for all three metals. In addition, the coupling in between metal-containing chains is at least one order of magnitude smaller than the magnetism within the chain, making these materials almost perfect one-dimensional magnets at low temperature. The in-between chain-coupling is found to be antiferromagnetic (i.e., no magnetism), in agreement with experiments. While some quasi-one-dimensional materials with one-dimensional magnetism exist, such as complex oxides, polymers, and a few other rare materials, these are typically very difficult to synthesize and often poisonous or explosive. The impact of this research stems from the ease of MOF-74 synthesis, resulting in a system that is arguably the simplest realization of one-dimensional magnetism in nature. In view of the high tailorability and tunability of MOFs, exciting new opportunities open up with possible impact for many magnetic devices.

Contact

Yves Chabal
University of Texas-Dallas
chabal@utdallas.edu

Timo Thonhauser
Wake Forest University
thonhauser@wfu.edu

Funding

This paper was supported by the Department of Energy, Office of Science, Basic Energy Sciences.

Publications

P. Canepa, Y. Chabal, and T. Thonhauser, “When metal organic frameworks turn into linear magnets”, Phys. Rev. B 87, 094407 (2013). [DOI: 10.1103/PhysRevB.87.094407]

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