Beijing National Laboratory for Molecular Sciences, Beijing Key Laboratory of Magnetoelectric Materials and Devices, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China
基金项目：
the National Natural Science Foundation of China(21671008);the National Natural Science Foundation of China(21621061);the National Key Basic Research Program of China(2018YFA0306003)
Beijing National Laboratory for Molecular Sciences, Beijing Key Laboratory of Magnetoelectric Materials and Devices, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China
Abstract:
Inorganic-organic or hybrid perovskite materials, which are the complementary counterparts of pure inorganic perovskites, can provide many new opportunities in the researches of phase transitions, critical phenomena, and relevant properties, as they combine the characteristics of inorganic and organic components. Therefore, the hybrid perovskites of ammonium metal formate framework are very promising, and their properties have been found to be strongly dependent on the characteristics of the constituent metal ions and/or ammonium ions. Herein, we used solid solution strategies, borrowed from solid state chemistry, to investigate the anisotropic diluted magnetic hybrid perovskite system of CH3NH3]CoxZn1-x(HCOO)3], wherein the B-sites are occupied by the mixed metal ions of Co2+ and Zn2+. The solid solution compounds of this series in the range x = 0–1 (or the molar percent Co% = 0–100%) were successfully prepared using conventional solution chemistry methods. The resulting compounds were demonstrated to be iso-structural by using both single-crystal and powder X-ray diffraction analyses. The solid solution crystals belong to the orthorhombic space group Pnma, with the cell parameters being a = 8.3015(2)–8.3207(3) Å, b = 11.6574(4)–11.6811(5) Å, c = 8.1315(3)–8.1427(4) Å, and V = 787.89(5)–790.98(7) Å3. The perovskite structure consists of a simple cubic anionic metal-formate framework and CH3NH3+ cations which are located in the framework cavities, with N―H···O hydrogen bonds formed between the framework and the cation. The members of this series showed negligible changes (< 0.4%) in their respective lattice and structural parameters. Thus, the prepared solid solution compounds constitute good molecule-based examples for the study of magnetic dilution under almost the same structural parameters and molecular geometries. Upon dilution, the magnetization per mole of Co at low temperatures and low fields was suppressed by the magnetic anisotropy of Co2+ and gradual destruction of the large spin canting between coupled Co2+ ions, in contrast to the magnetization enhancement observed in the isotropic diluted system of CH3NH3]MnxZn1-x(HCOO)3] with the same perovskite structure. The percolation limit was estimated as (Co%)P = 27(1)% (or xP = 0.27(1)) from the magnetic data, which was slightly lower than that predicted by the percolation theory for a simple cubic lattice (31%); this trend was due to the strong magnetic anisotropy of the present system. In addition, rare incommensurate phase transitions were primarily detected below ~120 K for the pure Co and Zn members, which may also affect the magnetic properties of the materials.
