Quantum tunneling and quantum phase interference in a [Mn(II)2Mn(III)2] single-molecule magnet.
Quantum tunneling and quantum phase interference in a [Mn(II)2Mn(III)2] single-molecule magnet.
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DOI：
10.1021/ja050994z
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发表时间：
2005-08
影响因子：
15
通讯作者：
L. Lecren;W. Wernsdorfer;Yang-guang Li;O. Roubeau;H. Miyasaka;R. Clérac
中科院分区：
文献类型：
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作者：
L. Lecren;W. Wernsdorfer;Yang-guang Li;O. Roubeau;H. Miyasaka;R. Clérac
[Mn4(hmp)6(H2O)2(NO3)2](NO3)2.2.5H2O(1)由2-羟甲基吡啶（Hhmp）与Mn(NO3)2.4H2O在四乙基氢氧化铵存在下反应合成。1在三斜P空间群中结晶，在填料结构中有两个晶体独立的中心对称[Mn4(hmp)6(H2O)2(NO3)2]2+配合物。四个锰离子呈双立方排列，其中外锰离子为七配位，内锰离子为六配位。直流磁测量表明，Mn2+…Mn3+和Mn3+…Mn3+相互作用为铁磁性，分别为J(wb)/k(B) = +0.80(5) k和J(bb)/k(B) = +7.1(1) k，基态为S(T) = 9。结合交流和直流测量揭示了1在热激活和基态隧穿机制下的单分子磁体（SMM）行为，包括量子相位干涉。在热激活状态下，系统的特征弛豫时间（tau）遵循Arrhenius定律，tau = 6.7 x 10(-)(9) s, δ (eff)/k(B) = 20.9 k。在0.34 K以下，tau饱和，表明磁化的量子隧穿成为smm的主要弛豫过程。在0.04 K以下，使用mu-SQUID技术测量的磁场依赖性显示smm之间存在非常弱的相互作用(zJ'/ K (B)约为-1.5 x 10(-3) K)，并且可以在-0.35 K处估计D/ K (B)。利用量子相位干涉确认了D值，并估计了横向各向异性参数E/k(B) = +0.083 k和基态隧道分裂δ (LZ) = 3 × 10(-7) k在H(trans) = 0 Oe。这些结果合理化了观察到的隧穿时间（tau(QTM)）和有效能垒（delta(eff)）。
[Mn4(hmp)6(H2O)2(NO3)2](NO3)2.2.5H2O (1) has been synthesized from the reaction of 2-hydroxymethylpyridine (Hhmp) with Mn(NO3)2.4H2O in the presence of tetraethylammonium hydroxide. 1 crystallizes in the triclinic P space group with two crystallographically independent centrosymmetrical [Mn4(hmp)6(H2O)2(NO3)2]2+ complexes in the packing structure. Four Mn ions are arranged in a double-cuboidal fashion where outer Mn2+ are heptacoordinated and inner Mn3+ are hexacoordinated. dc magnetic measurements show that both Mn2+...Mn3+ and Mn3+...Mn3+ interactions are ferromagnetic with J(wb)/k(B) = +0.80(5) K, and J(bb)/k(B) = +7.1(1) K, respectively, leading to an S(T) = 9 ground state. Combined ac and dc measurements reveal the single-molecule magnet (SMM) behavior of 1 with both thermally activated and ground-state tunneling regimes, including quantum phase interference. In the thermally activated regime, the characteristic relaxation time (tau) of the system follows an Arrhenius law with tau0 = 6.7 x 10(-)(9) s and delta(eff)/k(B) = 20.9 K. Below 0.34 K, tau saturates indicating that the quantum tunneling of the magnetization becomes the dominant relaxation process as expected for SMMs. Down to 0.04 K, field dependence of the magnetization measured using the mu-SQUID technique shows the presence of very weak inter-SMM interactions (zJ'/k(B) approximately -1.5 x 10(-3) K) and allows an estimation of D/k(B) at -0.35 K. Quantum phase interference has been used to confirm the D value and to estimate the transverse anisotropic parameter to E/k(B) = +0.083 K and the ground-state tunnel splitting delta(LZ) = 3 x 10(-7) K at H(trans) = 0 Oe. These results rationalize the observed tunneling time (tau(QTM)) and the effective energy barrier (delta(eff)).