A new manganese-based single-molecule magnet with a record-high antiferromagnetic phase transition temperature

We perform both dc and ac magnetic measurements on the single crystal of Mn30（Et-sao）3（C104）（MeOH）3 single- molecule magnet （SMM） when the sample is preserved in air for different durations. We find that, during the oxidation process, the sample develops into another SMM with a smaller anisotropy energy barrier and a stronger antiferromagnetic intermolecular exchange interaction. The antiferromagnetic transition temperature observed at 6.65 K in the new SMM is record-high for the antiferromagnetic phase transition in all the known SMMs. Compared to the original SMM, the only apparent change for the new SMM is that each molecule has lost three methyl groups as revealed by four-circle x-ray diffraction （XRD）, which is thought to be the origin of the stronger antiferromagnetic intermolecular exchange interaction.     

Mn12-Ac磁性分子团簇单晶的热重-差热分析与结构转变

通过热重-差热分析(TG-DTA)，考察了Mn12-Ac磁性分子晶体从室温到270℃的热失重过程.结合x射线粉末衍射分析，认为在第一个失重阶段，即25—110℃，Mn12-Ac失去了处于团簇分子间隙的结晶乙酸和结晶水，同时失去了团簇分子中与4个Mn3+配位的4个H2O，Mn12-Ac单晶结构被破坏，但是团簇分子的基本结构依然存在；在第二个失重阶段，即180—230℃，Mn12-Ac转变为γ-Mn2O3，其中混有少量Mn3O4. 关键词： Mn12 分子团簇 热重-差热分析 x射线衍射     

Dipolar Interaction and Magnetic Ordering Ground State in Mn12 Molecular Magnet

Here a direct calculation of the dipolar interaction in a single crystal Mn12, with all of Mn ions summed, shows that a transition between ferromagnetic and antiferromagnetic ground states takes place where the dimension along the α（b） axis versus the dimension along the c axis reaches a certain critical value. It is shown that the w ~ ~ ground state is dependent upon the shape of the specimen. The reason of the shape dependence of ordering is that dipolar interaction is of long-range nature and the sign of dipolar interaction is dependent on the direction.     

液膜富集－原子吸收法测定碱金属盐中的铜、钴、镍

液膜富集－原子吸收法测定碱金属盐中的铜、钴、镍于惠芬，王爱霞，王云平，徐书绅，杨光强（长春师范学院化学系长春　１３００３２）关键词液膜富集，铜，钴，镍，原子吸收法应用乳状液膜富集痕量金属，在分析化学领域是一种新方法，已有一些文献报道［１－３］。本文在...     

痕量镁的准液膜富集与测定

用准液膜法分离富集矿泉水、果茶中痕量镁,以火焰原子吸收法(AAS)测定其含量.用磷酸二异辛酯(P204)迁移Mg~(2 )离子,用硫酸解吸Mg~(2 )离子.迁移与解吸同步进行,省去了乳状液膜分离法中制乳及破乳过程,使液-液萃取与反萃取过程一步完成.在本法的液膜体系及操作条件下,镁的回收率在90%～94%范围,改善了AAS法的测定下限.1 仪器与试剂WYX-402A原子吸收分光光度计镁标准溶液(光谱纯):1000μg·ml~(-1)2 试验方法配制含4%～6%P204和0.05%～0.1%聚双丁二酰亚胺(N205)的煤油-CCl_4溶液作为萃取剂(ρ为1.08g·ml~(-1)),将其加入到分离装置的分离柱中,使液面达到解吸剂硫酸注入口.蠕动注入解吸剂1.16g·ml~(-1)硫酸.当液面超过硫酸注入口1cm左右时,蠕动注入含镁料液(ρ为1.10g·ml~(-1)的0.01mol·ml~(-1)HOAc-NaOAc体系).连续蠕动注入料液及解吸剂以保持上油水界面在硫酸注入口与料液出口之间,下油水界面低于料液注入口,料液循环六次以上.停止蠕动注入料液后,连续循环注入解吸剂5min,静止分层后从分离柱下口活栓放出解吸剂并直接用于测定.     

液膜富集与火焰原子吸收光谱法测定饮料中痕量锌

液膜法是一种新型高效的分离技术.近年来,作者等已有多篇报道,但在食品分析中尚无应用报道.锌是人体中不可缺少的微量元素,饮料或口服液中痕量锌的分析一般先作灰化处理,然后以火焰原子吸收光谱法测定.本文以液膜法作为预处理手段,较之常用的灰化法更为省时省力,所得结果与文献[7]方法一致,而分析周期则由3h缩至1h.     

Magnetic Quantum Tunnelling in Faster Relaxation Process in Mn12Ac Molecular Magnets

The field-tuned ac susceptibility of Mn12Ac single crystal has been measured as functions of temperature and frequency. Two relaxation processes appear in our measurement. One is related to the magnetic quantum tunnelling of a collective spin S = 12 by a 61 K magnetic barrier and it has been well studied, while the other is faster than the former and its mechanism is unclear. We find that the relaxation time for the faster process shows the minima at H = 0 and H = 3.4 kOe, indicating that the quantum tunnelling also takes place in this process while the resonant fields are different from what we have known before.     

Quantum interference between Raman scattering and single-photon absorption

A new kind of quantum interference between Raman scattering and single-photon absorption is predicted theoretically, which gives an expanded view of quantum interference. Its potential application is also proposed.     

Shape Dependence of Low-Temperature Magnetic Relaxation of Mn12Ac

We report the discovery that the low-temperature magnetic relaxation in Mn12Ac single crystals strongly depends on the shape of the samples. The relaxation time exhibits a minimum at the phase transition point between ferromagnetic and antiferromagnetie phases. The shape dependence is attributed to the dipolar interaction between molecular magnets.     

Magnetic Relaxation Study on Single Crystals of Nia Single-Molecule Magnets

The ac susceptibility of single crystals of Ni4 single-molecule magnets is measured by a compensation measurement setup. The magnetic relaxation time calculated from the peak of the out-phase component of the susceptibility fits the Arrhenius law well and gives an effective spin-flipping energy barrier of Uefr = 7.2 K. This value is fax below the classical activation energy barrier of U = 14 K, whereas it is close to the energy gap between the Sz= ±4 and S, = ±3 doublets, which indicates that quantum tunneling between the Sz = 3 and Sz = -3 states plays a key role in the magnetic relaxation. Therefore the relaxation process combines thermal activation and quantum tunneling. Also we deduce that the blocking temperature of Ni4 single-molecule magnets is lower than 0.3 K by extrapolating the relaxation time plot, which ensures that this single-molecule magnet material enters a long-range magnetic ordered state instead of a spin glass state at 0.91 K.