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首页> 外文期刊>Chemistry: A European journal >A Wheel-Shaped Single-Molecule Magnet of [Mn~(II))_3Mn~(III)_4]: Quantum Tunneling of Magnetization under Static and Pulse Magnetic Fields
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A Wheel-Shaped Single-Molecule Magnet of [Mn~(II))_3Mn~(III)_4]: Quantum Tunneling of Magnetization under Static and Pulse Magnetic Fields

机译：[Mn〜（II））_ 3Mn〜（III）_4的轮型单分子磁体：在静磁场和脉冲磁场下的磁化量子隧穿

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The reaction of N-(2-hy-droxy-5-nitrobenzyl)iminodiethanol (= H3(5-NO2-hbide)) with Mn(OAc)_2 centre dot 4H2O in methanol, followed by recrys-tallization from 1,2-dichloroethane, yielded a wheel-shaped single-molecule magnet (SMM) of [Mn~(II)_3Mn~(III)_4(5-NO2-hbide)_6] centre dot 5C2H4Cl2 (1). In 1, seven manganese ions are linked by six tri-anionic ligands and form the wheel in which the two manganese ions on the rim and the one in the center are Mn~(II) and the other four manganese ions are Mn~(III) ions. Powder magnetic susceptibility measurements showed a gradual increase with chi_mT values as the temperature was lowered, reaching a maximum value of 53.9 emu mol~(-1)K. Analyses ofmagnetic susceptibility data suggested a spin ground state of S = 19/2. The zero-field splitting parameters of D and B_4~0 were estimated to be -0.283(1) K and -1.64(1) x 10~(-5) K, respectively, by high-field EPR measurements (HF-EPR). The anisotropic parameters agreed with those estimated from magnetization and inelastic neutron scattering experiments. AC magnetic susceptibility measurements showed frequency-dependent in- and out-of-phase signals, characteristic datafor an SMM, and an Arrhenius plot of the relaxation time gave a re-orientation energy barrier (DELTA E) of 18.1 K and a pre-exponential factor of 1.63 x 10~(-7) s. Magnetization experiments on aligned single crystals below 0.7 K showed a stepped hysteresis loop, confirming the occurrence of quantum tunneling of the on magnetization (QTM). QTM was, on the other hand, suppressed by rapid sweeps of the magnetic field even at 0.5 K. The sweep-rate dependence of the spin flips can be understood by considering the Landau-Zener-Stiick-elberg (LZS) model.
机译：N-（2-羟基-5-硝基苄基）亚氨基二乙醇（= H3（5-NO2-hbide））与Mn（OAc）_2中心点4H2O在甲醇中的反应，然后从1,2-进行重结晶二氯乙烷制得[Mn〜（II）_3Mn〜（III）_4（5-NO2-hbide）_6]中心点5C2H4Cl2（1）的轮状单分子磁体（SMM）。在1中，七个锰离子通过六个三阴离子配体相连，形成一个轮，其中轮辋上的两个锰离子和中心的一个锰离子为Mn〜（II），其他四个锰离子为Mn〜（III ）离子。粉末磁化率测量结果表明，随着温度的降低，chi_mT值逐渐增加，最大值达到53.9 emu mol〜（-1）K。磁化率数据分析表明自旋基态为S = 19/2。通过高场EPR测量（HF-EPR），D和B_4〜0的零场分裂参数分别估计为-0.283（1）K和-1.64（1）x 10〜（-5）K 。各向异性参数与磁化和非弹性中子散射实验估计的参数一致。交流磁化率测量显示，频率相关的同相和异相信号，SMM的特征数据以及弛豫时间的Arrhenius图给出了18.1 K的重新定向能垒（DELTA E）和指数前系数1.63 x 10〜（-7）s。在低于0.7 K的取向单晶上进行的磁化实验显示出阶梯状的磁滞回线，证实了on磁化（QTM）的量子隧穿的发生。另一方面，即使在0.5 K时，磁场的快速扫描也抑制了QTM。自旋翻转的扫描速率依赖性可以通过考虑Landau-Zener-Stiick-elberg（LZS）模型来理解。

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