An unusual magnetic phenomenon in Mg doping [(CH₃)₂NH₂] Co_xMg_1−x[HCOO]₃ frameworks

¹ School of Science, China University of Geosciences Beijing - No. 29 College Road, Haidian District, Beijing, China
² Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences No. 8 South Third Street, Zhongguancun, Beijing, China
³ China University of Geosciences - No. 29 College Road, Haidian District, Beijing, China

^(a) E-mail: fanzj@cugb.edu.cn (corresponding author)
^(b) E-mail: xhsong@iphy.ac.cn (corresponding author)

Received: 15 August 2022
Accepted: 18 November 2022

Abstract

In this study, Mg doping metal-organic frameworks (MOFs) [(CH₃)₂NH₂] Co_1−xMg_x[HCOO]₃ single crystals were synthesized by solvothermal method with normal ratios x = 0, 0.1, 0.2, 0.3, 0.4, 0.6. Powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) results showed that Mg ion is uniformly doped into Co-based MOFs crystal. With the increase of diamagnetic magnesium ions doping, the antiferromagnetic phase transition temperature of Co-based MOFs for pure Co-MOF decreased from 15 K to 7.5 K for x = 0.4. Abnormal larger magnetic hysteresis was obtained for Mg doping crystals with a large coercive field 3100 Oe (x = 0.1), 3700 Oe (x = 0.2), 2900 Oe (x = 0.3) compared with 600 Oe coercive field for pure Co-MOFs (x = 0). At the same time, step-like behavior was first observed on Mg²⁺ doping sample with x = 0.1–0.3. This unusual magnetic phenomenon is well interpreted based on the coexistence of long-range canted antiferromagnetic order and isolated single-ion quantum magnets. The diamagnetic magnesium ions doping decreases the strong exchange coupling between neighboring Co ions and step-like behavior stemmed from the quantum tunneling of isolated Co ions.