Abnormal magnetic phenomenon at low temperature in Zn doped <inline-formula><tex-math id="M1">\begin{document}$ \left[{(\mathbf{C}\mathbf{H}}_{3}{)}_{2}\mathbf{N}{\mathbf{H}}_{2}\right]{\mathbf{C}\mathbf{o}}_{\mathit{x}}{\mathbf{Z}\mathbf{n}}_{1-\mathit{x}}{\left[\mathbf{H}\mathbf{C}\mathbf{O}\mathbf{O}\right]}_{3} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M1.png"/></alternatives></inline-formula> frameworks
Authors: Liu Rong-Zhao , Fan Zhen-Jun , Wang Hao-Cheng , Ning Hao-Ming , Mi Zhen-Yu , Liu Guang-Yao , Song Xiao-Hui ,   School of Science, China University of Geosciences Beijing, Beijing 100083, China,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   Institute of Earth Sciences, China University of Geosciences Beijing, Beijing 100083, China,   State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences Beijing, Beijing 100083, China
Published: November 2022

Metal-organic framework (MOF) is a new type of inorganic-organic hybrid porous material composed of organic ligands bridging metal ions, and it has the characteristics of tunable functions, good stability and porosity. In this study, Zn doped Co-based metal organic frame works single-crystal samples<inline-formula><tex-math id="M2">\begin{document}$\left[{(\rm{C}\rm{H}}_{3}{)}_{2}\rm{N}{\rm{H}}_{2}\right]{\rm{C}\rm{o}}_{1-x}{\rm{Z}\rm{n}}_{x} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M2.png"/></alternatives></inline-formula><inline-formula><tex-math id="M2-1">\begin{document}$ {\left[\rm{H}\rm{C}\rm{O}\rm{O}\right]}_{3}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M2-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M2-1.png"/></alternatives></inline-formula>are synthesized by the solvothermal method with normal ratio <i>x</i> = 0, 0.1, 0.2, 0.3, 0.4, 0.5. Single crystal diffraction, scanning electron microscope and energy dispersive X-ray spectroscopy results show that Zn ions are uniformly doped into Co-based MOFs crystals. The field cooling curves show that antiferromagnetic phase transition temperature of Co-based MOFs decreases from 15 K for pure Co-MOF <i>x</i> = 0 to 12.8 K for <i>x</i> = 0.2. Abnormal large magnetic hysteresis is obtained for Zn doped crystals with large coercive field 3600 Oe (<i>x</i> = 0.3) compared with 450 Oe coercive field for pure Co-MOF (<i>x</i> = 0), and the hysteresis area of Zinc-doped sample is more than 3 times that of pure cobalt sample. On the other hand, we find a series of steps on the hysteresis loop of DMCo<sub>0.9</sub>Zn<sub>0.1</sub>F sample, which gradually disappears with the increase of temperature, similar to the quantum tunneling phenomenon of a single molecule magnet. Previous studies have shown that the long range magnetic interaction and the magnetic single-ion behavior competition coexist in these systems. It is believed that the doping of non-magnetic zinc ions weakens the long-range interaction between Co ions and makes Co ions show the step effect caused by quantum tunneling at low temperature.