摘要
高对称性晶体场环境下的各向异性镧系离子有利于消除其非轴向磁各向异性,并且在较大程度上抑制量子隧穿效应(QTM),从而有利于增加单分子磁体(SMMs)的磁弛豫有效能垒(Ueff)、提高其阻塞温度(TB).而研究较少的各向同性GdⅢ离子表现出不寻常的场诱导磁弛豫性质,其弛豫机理仍然存在争议.本研究采用六氰合铁酸钾作为氰基前驱体以及具有较大空间位阻的2-甲基吡啶氮氧化物(2-PNO)作为辅助配体,使用溶剂挥发法与稀土GdⅢ离子构筑氰基桥连GdFe配合物,并进行结构表征、磁学性质探究.单晶X射线衍射结果表明配合物GdFe中GdⅢ离子的配位环境为具有局部高对称性且轴向拉伸的五角双锥型(D5h)配位几何结构.零直流场下GdFe配合物的交流磁化率没有表现出频率依赖性,应是量子隧穿效应所致,而在外加1 kOe直流场条件下则显示出磁弛豫行为,表明QTM过程被抑制.其直流场诱导磁弛豫行为可归结为一个由共振声子俘获所产生的声子瓶颈效应以及一个低温下未被完全抑制的QTM过程.该GdFe配合物可看作研究稀土GdⅢ离子在局部高对称性(如这里的D5h)配位几何条件下磁弛豫性质的典型实例.
Anisotropic lanthanide ions in the highly symmetric crystal field environment are beneficial to eliminate their non-axial magnetic anisotropy and to suppress the quantum tunneling effect(QTM)to a large extent,thus increasing the effective energy barrier(U eff)of magnetic relaxation and improving the blocking temperature(T B)for single-molecule magnets(SMMs).However,the less-studied isotropic GdⅢions exhibit anomalous field-induced magnetic relaxation properties,and the relaxation mechanism remains controversial.In this paper,potassium hexacyanoferrate was used as the cyano-precursor and 2-picoline N-oxide(2-PNO)with large steric hindrance as the auxiliary ligand,and the complex GdFe was constructed with rare earth GdⅢions by solvent evaporation method.The structure characterization and magnetic properties were investigated.The single crystal X-ray diffraction results show that the coordination environment of GdⅢions in the complex GdFe is a highly-symmetric axially-elongated pentagonal bipyramidal(D 5h)coordination geometry.The AC(alternating current)susceptibility of the GdFe complex under zero DC(direct current)field does not show frequency dependence,which should be caused by quantum tunneling effect,while it shows magnetic relaxation behavior under a 1 kOe external field,indicating that the QTM process is suppressed.The DC field-induced relaxation behavior can be attributed to a phonon bottleneck effect caused by resonant phonon trapping and a QTM process that is not completely suppressed at low temperature.This GdFe complex can be regarded as a typical example to study the magnetic relaxation properties of rare earth GdⅢions under local high-symmetry(here D 5h)coordination geometry.
作者
方玥懿
刘贝
谷依
赵曼芸
董晓燕
朱文华
FANG Yueyi;LIU Bei;GU Yi;ZHAO Manyun;DONG Xiaoyan;ZHU Wenhua(College of Chemistry and Chemical Engineering,Hubei University,Wuhan 430062,China)
出处
《湖北大学学报（自然科学版）》
CAS
2023年第5期758-765,共8页
Journal of Hubei University：Natural Science
基金
国家自然科学基金(22271082)
湖北省教育厅重点项目(D20211003)资助
关键词
各向同性钆离子
高对称性
磁弛豫
声子瓶颈效应
isotropic GdⅢions
high-symmetry
magnetic relaxation
phonon bottleneck effect
