Berry Tanya, Morey Jennifer R, Arpino Kathryn E, Dou Jin-Hu, Felser Claudia, Dincǎ Mircea, McQueen Tyrel M
Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States.
Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, United States.
Inorg Chem. 2022 May 2;61(17):6480-6487. doi: 10.1021/acs.inorgchem.2c00081. Epub 2022 Apr 21.
Metal-organic frameworks (MOFs) provide exceptional chemical tunability and have recently been demonstrated to exhibit electrical conductivity and related functional electronic properties. The kagomé lattice is a fruitful source of novel physical states of matter, including the quantum spin liquid (in insulators) and Dirac fermions (in metals). Small-bandgap kagomé materials have the potential to bridge quantum spin liquid states and exhibit phenomena such as superconductivity but remain exceptionally rare. Here we report a structural, thermodynamic, and transport study of the two-dimensional kagomé metal-organic frameworks Ni(HIB) and Cu(HIB) (HIB = hexaiminobenzene). Magnetization measurements yield Curie constants of 0.989 emu K (mol Ni) Oe and 0.371 emu K (mol Cu) Oe, respectively, close to the values expected for ideal = 1 Ni and = / Cu. Weiss temperatures of -10.6 and -14.3 K indicate net weak mean field antiferromagnetic interactions between ions. Electrical transport measurements reveal that both materials are semiconducting, with gaps () of 22.2 and 103 meV, respectively. Specific heat measurements reveal a large -linear contribution γ of 148(4) mJ mol-fu K in Ni(HIB) with only a gradual upturn below ∼5 K and no evidence of a phase transition to an ordered state down to 0.1 K. Cu(HIB) also lacks evidence of a phase transition above 0.1 K, with a substantial, field-dependent, magnetic contribution below ∼5 K. Despite them being superficially in agreement with the expectations of magnetic frustration and spin liquid physics, we ascribe these observations to the stacking faults found from a detailed analysis of synchrotron X-ray diffraction data. At the same time, our results demonstrate that these MOFs exhibit localized magnetism with simultaneous proximity to a metallic state, thus opening up opportunities to explore the connection between the insulating and metallic ground states of kagomé materials in a highly tunable chemical platform.
金属有机框架材料（MOFs）具有出色的化学可调性，最近已被证明具有导电性及相关的功能性电子特性。蜂窝晶格是产生新型物质物理状态的丰富来源，包括量子自旋液体（在绝缘体中）和狄拉克费米子（在金属中）。小带隙蜂窝材料有可能连接量子自旋液体状态并展现出超导等现象，但仍然极为罕见。在此，我们报告了二维蜂窝金属有机框架材料Ni(HIB)和Cu(HIB)（HIB = 六亚氨基苯）的结构、热力学和输运研究。磁化测量分别得出居里常数为0.989 emu K（mol Ni）Oe和0.371 emu K（mol Cu）Oe，接近理想的(S = 1) Ni和(S = 1/2) Cu预期的值。-10.6和-14.3 K的魏斯温度表明离子之间存在净弱平均场反铁磁相互作用。电输运测量表明这两种材料均为半导体，带隙（(E_g)）分别为22.2和103 meV。比热测量显示，Ni(HIB)中存在148(4) mJ mol⁻¹ K⁻¹的大线性贡献(\gamma)，在约5 K以下仅逐渐上升，且在降至至0.1 K时没有向有序状态相变的迹象。Cu(HIB)在0.1 K以上也没有相变的迹象，在约5 K以下有显著的、与场相关的磁贡献。尽管这些观察结果表面上与磁阻挫和自旋液体物理的预期相符，但我们将这些观察结果归因于通过同步加速器X射线衍射数据的详细分析发现的堆垛层错。同时，我们的结果表明这些MOFs表现出局域磁性，同时接近金属态，从而在一个高度可调的化学平台上为探索蜂窝材料的绝缘和金属基态之间的联系提供了机会。
