Unusual magnetic phenomenon at low temperature in Zn doping [(CH3)2NH2]CoxZn1-x[HCOO]3 frameworks

Metal-organic frameworks (MOFs)are new types of inorganic-organic hybrid porous materials composed of organic ligands bridging metal ions which has the characteristics of regulable functions, good stability and porosity. In this study, Zn doping Co-based metal organic frameworkssingle-crystal samples [(CH3)2NH2]CoxZn1-x[HCOO]3 were synthesized by solvothermal method with normal ratio x=0, 0.1, 0.2, 0.3, 0.4, 0.5. Single crystal diffraction, SEM and EDX results show that Zn ions are uniformly doped into Co-based MOFs crystals. Field cooling curves show that antiferromagnetic phase transition temperature of Co-based MOFs decreases from 15 K for pure Co-MOF x=0 to 12.8 K for x=0.2. Abnormal large magnetic hysteresis is obtained for Zn doping crystals with large coercive field 3600 Oe (x=0.3) compared with 450 Oe coercive field for pure Co-MOFs (x=0), and the hysteresis area of Zinc-doping sample is more than 3 times that of pure cobalt sample. On the other hand, we found a series of steps on the hysteresis loop of DMCo0.9Zn0.1F sample, which gradually disappeared with the increase of temperature, similar to the quantum tunneling phenomenon of a single molecule magnet. Previous studies have shown that the coexistence of long range magnetic interaction and magnetic single-ion behavior competition 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.