Triangular Paramagnetic Molecules as Mimics of Long-Range Phenomena in Bulk Magnets

Shubham Bisht¹, Wei-Hao Chou², James Wampler³, Vivien Zapf³, Steven Hill², Michael Shatruk¹

1Florida State University, Department of Chemistry & Biochemistry, Tallahassee FL 32306, USA
2Los Alamos National Laboratory, NM 87545, 3National High Magnetic Field Laboratory Tallahassee, FL 32310

Over the last three decades, fruitful research in molecular magnetism enabled manifestation of several solid-state magnetic phenomena in molecular systems. Perhaps, the most striking example is the discovery of single-molecule magnetism in a dodecanuclear mixed-valent Mn₁₂ cluster¹, which not only showed a magnetic hysteresis characteristic of bulk ferromagnets, but also demonstrated unique quantum tunneling steps that only occur in molecular magnets². Inspired by this discovery, we are interested in designing and investigating molecules that can mimic such bulk magnetic properties as spin-electric coupling (SEC) and quantum spin liquid (QSL). Efficient SEC coupling leads to multiferroic behavior, when ferroelectricity and ferromagnetism coexist³. In QSL, strong magnetic frustration prevents ordering of spins even at the lowest temperature possible⁴. To develop these ideas at the molecular level, we use synthetic inorganic chemistry to tune the atomistic interactions as needed for the desired properties. To achieve molecule-based SEC effects, we explore the influence of applied magnetic (electric) field on electric (magnetic) polarization in spin-frustrated triangular complexes, such as [Ru^III(μ³-O)(PhCOO)₆(py)₃]PF₆. We expect that the applied field can break the symmetry imposed by the equilateral arrangement of the Ru^III ions and produce a substantial change in the measured electric or magnetic polarization. Our search for molecule-based QSL mimics relies on the intriguing theoretical prediction of QSL in the Kitaev system, defined by bond-directional exchange interactions among strongly anisotropic spins arranged on a triangular lattice. To achieve a molecular system with Kitaev-like interactions, we have synthesized a tetranuclear cluster, [Ni(cyclen)]₃[Cr(ox)₃](ClO₄)₃, and characterized its structural and magnetic properties. Our future efforts will aim to extend this design strategy to obtain such clusters with more magnetically anisotropic metal ions, to allow for the bond-directional anisotropy of magnetic exchange interactions.

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