化学学报 ›› 2013, Vol. 71 ›› Issue (07): 1022-1028.DOI: 10.6023/A13030319 上一篇    下一篇

研究论文

单核Gd化合物的场依赖磁弛豫和磁热效应研究

钱康a, 王炳武a, 王哲明a, 苏刚b, 高松a   

  1. a 北京大学化学与分子工程学院稀土材料化学与应用国家重点实验室 北京 100871;
    b 中国科学院大学物理学院 北京 100049
  • 收稿日期:2013-03-21 出版日期:2013-07-14 发布日期:2013-05-06
  • 通讯作者: 高松, E-mail: gaosong@pku.edu.cn E-mail:gaosong@pku.edu.cn
  • 基金资助:

    项目受国家自然科学基金(No. 90922033)和国家重点基础研究发展计划(Nos. 2010CB934601, 2013CB933400)资助.

Field-Dependent Magnetic Relaxation and Magnetocaloric Effect in Mononuclear Gd Complexes

Qian Kanga, Wang Bingwua, Wang Zheminga, Su Gangb, Gao Songa   

  1. a State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecule Engineering, Peking University, Beijing 100871;
    b School of Physics, University of Chinese Academy of Sciences, Beijing 100049
  • Received:2013-03-21 Online:2013-07-14 Published:2013-05-06
  • Supported by:

    Project supported by the National Natural Science Foundation of China (No. 90922033) and the National Basic Research Program of China (Nos. 2010CB934601, 2013CB933400).

合成了两例具有局域D4d对称性的单核钆配合物: Gd(THD)3L (THD=2,2,6,6-四甲基庚烷-3,5-二酮, L=Phen (1,10-菲罗琳, 1), Bpy (2,2'-联吡啶, 2). 磁性研究表明其在低温下具有较大的磁热效应, 在2.5 K时, 0到5 T外磁场下的磁熵变(-ΔSm)分别高达17.0和18.4 J·kg-1·K-1. 研究发现, 化合物1, 2还同时具有明显的场依赖磁弛豫性质. 通过分析弛豫时间随外加磁场和温度变化的关系, 发现其低场下的弛豫行为可以用共振声子俘获机制来解释, 高场下的弛豫行为则可能来源于直接过程.

关键词: 钆, 场依赖磁弛豫, 磁热效应

Two new mononuclear Gd complexes Gd(THD)3L (THD=2,2,6,6-tetramethylheptane-3,5-dione, L=Phen (1), Bpy (2)) based on b-diketone type ligand with Phen and Bpy as capping ligands were synthesized, respectively. To obtain the complexes, the THD liangd (3 mmol) and capping ligand (1 mmol) were mixed and dissolved in ethanol (10 mL), followed by adding of 5 mL aqueous solution of KOH (3 mmol) and slowly heating to remove the α-H of THD ligand. And then 5 mL aqueous solution of Gd(NO3)3 was added dropwise. The white precipitate was collected and recrystallized in the mixture of ethanol and acetone to get colorless transparent crystals. Their structures were determined by the single-crystal X-ray diffraction method, found crystallized in P-1 space group, and gave an eight-coordinated coordination environment of Gd3-with D4d local symmetry. Magnetic susceptibility measurements of powder samples were carried out by SQUID magnetometer at 1000 Oe dc field from 2 to 300 K, and the χmT value at room temperatures were 7.89 and 8.25 cm3·K·mol-1, respectively, in good agreement with the expected value. The magnetization measurements reveal that the magnetic entropy changes (-ΔSm) at 2.5 K from 0 to 5 Tesla magnetic field are as large as 17.0 and 18.4 J·kg-1·K-1 for 1 and 2, respectively. The ac susceptibility shows an obvious slow magnetic relaxation phenomenon. By analyzing the temperature and magnetic field dependences of the relaxation time, we found that the resonant phonon trapping mechanism is predominant when the field is lower than 1 T and the direct process plays a role when the field is larger than 2 T.

Key words: Gd, field-dependent relaxation, magnetocaloric effect