Mn nuclear magnetic resonance studies in RMn2Ge2 (R = rare earths)

The ⁵⁵Mn NMR in RMn₂Ge₂ (R= La,Nd and Gd) were observed as a function of temperature. In Nd and Gd compounds the ⁵⁵Mn NMR frequencies exhibit anomalous temperature dependences owing the effects of rare earth sublattices. The ordering temperatures of the Nd and Gd sublattices are found to be 30 and 95 K, respectively.     

2018年5期 电子期刊

研究了不同Mn/Pb量比的Mn掺杂CsPbCl₃（Mn：CsPbCl₃）钙钛矿量子点的发光性质。Mn/Pb的量比增加引起的Mn²⁺发光峰的红移,被认为是来源于高浓度Mn²⁺掺杂下的Mn²⁺-Mn²⁺对。进一步研究了Mn：CsPbCl₃量子点的发光效率与Mn/Pb的量比之间的关系,发现随着量比达到5：1时,其发光效率明显下降。这种发光效率下降是由于Mn掺杂浓度引起的发光猝灭。Mn：CsPbCl₃量子点的变温发光光谱证实,随着温度的升高,Mn离子发光峰蓝移,线宽加宽,但其发光强度明显增加。     

ZnS：Mn/SiO2量子点的表面聚乙烯吡咯烷酮修饰及其应用于海水中铅离子检测

制备了二氧化硅壳层修饰的ZnS：Mn量子点,基于聚乙烯吡咯烷酮（PVP）与二氧化硅表面硅羟基的作用,在纳米复合微粒表面进行了PVP的修饰,得到了在海水中荧光性能及胶体稳定性良好的ZnS：Mn/SiO₂/PVP 量子点。在Pb²⁺对所制备纳米微粒具有荧光猝灭效应的基础上,建立了用ZnS：Mn/SiO₂/PVP 量子点作为荧光探针检测海水中微量铅离子的新方法。研究表明,量子点浓度为10^-3 mol/L时,海水中离子浓度在10~100 μmol/L范围内与ZnS：Mn/SiO₂/PVP量子点荧光猝灭强度呈良好的线性关系,相关系数为0.994 6,检出限为8×10^-7 mol/L。     

Heat capacities of Laves phase compounds RMn2 (R = Y, Gd and Er)

Measurements of heat capacity indicate that the Mn moment in YMn₂ has an itinerant character and an additional C_M is observable even above T_N. In GdMn₂, the Gd moments are in disorder at T_N simultaneously with the Mn moments. The CEF contributions in ErMn₂ are observed and are calculated using a single-ion Hamiltonian.     

Magnetic and structural investigations on substituted Pr2Co17-xTx systems (T= Fe, Mn, Cr, Cu and Al)

Magnetic and structural characteristics of Pr₂Co₁₇-based ternaries, in which Co is partly replaced by other transition elements, namely Fe, Mn, Cr, Cu and Al, have been investigated. The objective of the work was to explore the possibility of enhancing the anisotropy of Pr₂Co₁₇ to the point that it would be useful for permanent magnet fabrication. X-ray diffraction indicates that all the systems studied occur in the rhombohedral Th₂Zn₁₇ structure. The cell constants increase as Fe, Mn, etc., are introduced in the system, which indicates that substitution occurs in the Co sublattice. The Curie temperatures, T_c, decrease monotonically with increasing x in the order Fe < Cu < Mn < Al < Cr. The saturation magnetization, M_s, increases with increasing x for the Fe system with x 8. For x #62; 8 in the Pr₂Co_17-xFe_x system and in all other ternary systems st died, M_s decreases with x, the magnitude of the effect being in the order Cr #62; Al #62; Mn #62; Cu. The rate of decrease is larger than that expected as a simple dilution except for the systems containing Cu. Significant modification of the anisotropy characteristics of Pr₂Co₁₇ is observed upon substitution. The planar anisotropy of Pr₂Co₁₇ becomes uniaxial with Fe (x 4) and Mn (x 2) substitutions. With Cr and Al substitutions, the plane-seeking tendency of Pr₂Co₁₇ is significantly weakened.     

第一原理研究Mn掺杂LiNbO3晶体的磁性和光吸收性质

采用基于密度泛函理论和局域密度近似的第一性原理分析了Mn掺杂LiNbO₃晶体的结构, 磁性, 电子特性和光吸收特性. 文中计算了Mn占据Li位和Nb位体系的形成焓, 对应的形成焓分别为-8.340 eV/atom和-8.0062 eV/atom, 也就意味着Mn 原子优先占据Li位. 这也就意味着Mn原子占据Li位的掺杂LiNbO₃晶体结构更稳定. 磁性分析的结果显示, 其对应磁矩也比占据Nb位的高. 进一步分析磁性的来源, 自旋态密度结果显示: Mn掺杂LiNbO₃晶体的磁性主要源于掺杂原子Mn, Mn原子携带的磁矩高达 4.3 μ_B, 显示出高自旋结构. 由于Mn-3d与近邻O-2p及次近邻Nb-4d 轨道的杂化作用, 计算表明: 诱导近邻O原子及次近邻Nb原子产生的磁矩对总磁矩的贡献较小. 通过光学吸收谱的分析, 得出在可见光区Li位被Mn原子替代以后显示出更好的光吸收响应相比于Nb位. 本文还分析了O空位对于LiNbO₃晶体磁性与电子性质的影响, 结果显示O空位的存在可以增加Mn掺杂LiNbO₃体系的磁性.     

些V/S,V/Fe/S和Mn/O簇合物溶液化学行为的NMR研究

报道我们对某些V/S,V/Fe/S和Mn/O簇合物溶液化学的核磁研究.(Et₄N)[V₄S₄(C₄H₈NCS₂)₆](1)的¹H NMR谱包含三个宽峰,δ4.77,5.17和7.57,分别归属为端基与桥基配体的α-H.游离配体信号的出现表明了溶液中发生配体与溶剂分子的交换反应.对一系列[VFe₃S₄(R₂ NCS₂)₄]^-簇合物(R₂=OC₄H₈(2),Et₂(3))进行了¹H NMR表征.钒与三个铁中心的配体氢谱被分别归属.对NMR谱的时间跟踪发现位于δ19.6(2)以及δ34.2(3)的信号逐渐增长,这意味着新物种形成.合成反应的动态NMR跟踪指认了新物种为Fe₄S₄(R₂ NCS₂)₄.提出了溶液中簇骼金属原子交换机理.包含H₂O和NO₃配体的单核锰bpy配合物(4)的氢谱指示出这些单齿配体的可交换性.它促使配合物4成为含有两个单核Mn分子的包容化合物.     

An empirical study of the Mn partial density of states in icosahedral Al70Pd20Mn10

Using the line-shape analysis of the Mn 2p_3/23d3d Auger transitions and by observing the Mn 3p→3d transitions in electron energy-loss spectroscopy, we have studied the local density of electronic states of the crystalline cubic and the quasicrystalline icosahedral phases of Al₇₀Pd₂₀Mn₁₀. We find that, in the cubic phase the Mn 3d states coincide with the Fermi level E_F, but in the quasicrystalline state the Mn 3d band is fully occupied and shifted to lower binding energies causing a significant reduction in the density of states at E_F.     

Role of vacancy-type defects in magnetism of GaMnN

Role of vacancy-type(N vacancy(VN) and Ga vacancy(VGa)) defects in magnetism of GaMnN is investigated by first-principle calculation.Theoretical results show that both the VNand VGainfluence the ferromagnetic state of a system.The VNcan induce antiferromagnetic state and the VGaindirectly modify the stability of the ferromagnetic state by depopulating the Mn levels in GaMnN.The transfer of electrons between the vacancy defects and Mn ions results in converting Mn~(3+)(d~4) into Mn~(2+)(d5).The introduced VNand the ferromagnetism become stronger and then gradually weaker with Mn concentration increasing,as well as the coexistence of Mn~(3+)(d~4) and Mn~(2+)(d~5) are found in GaMnN films grown by metal–organic chemical vapor deposition.The analysis suggests that a big proportion of Mn~(3+)changing into Mn~(2+)will reduce the exchange interaction and magnetic correlation of Mn atoms and lead to the reduction of ferromagnetism of material.     

Regional distribution of manganese found in the brain after injection of a single dose of manganese-based contrast agents

Manganese (Mn) complexes are unstable and dissociate in vivo. Because of the release of this metal, there exists some concern about the potential long-term neurotoxicity associated with the use of Mn-based contrast agents. This latter problem arises because manganese is known to accumulate in specific regions of the brain of people intoxicated by this metal. It was previously demonstrated that Mn can accumulate in the mice brain after administration of 5 μmol/kg of MnCl₂, Mn-diethylenetriaminepentaacetate (Mn-DTPA), or Mn-dipyridoxal diphosphate (Mn-DPDP). In order to better characterize the behavior of Mn complexes after administration, this study assesses the regional distribution of Mn in the brain after i.v. injection of a single dose of MnCl₂ or Mn-DTPA. Male Wistar rats received an i.v. injection of 5 μmol/kg of ⁵⁴Mn as MnCl₂ or Mn-DTPA. The rats were killed at one and two weeks post exposure. The distribution of the radioactivity in the slices was monitored by autoradiography. For both MnCl₂ or Mn-DTPA, we observed that the radioactivity was dispersed in the entire brain, but the radioactivity was higher in several regions. No difference was observed between MnCl₂ or Mn-DTPA in the regional distribution of Mn, and no difference was observed between the two times of exposure (1 week or 2 weeks). The uptake of Mn was minimal in corpus callosum. Maximal Mn concentration was observed in the hippocampal region, thalamus, colliculi, amygdala, olfactory nuclei, and cerebellum.     

Neutron diffraction study of magnetic ordering in ErMn2Si2, ErMn2Ge2 and ErFe2Si2

Neutron diffraction study of polycrystalline compounds ErMn₂Si₂, ErMn₂Ge₂ and ErFe₂Si₂ was performed in the temperature range between 1.8 and 293 K. All compounds have tetragonal, ThCr₂Si₂-type crystal structure. The antiferromagnetic collinear structure of ErMn₂Si₂ and ErMn₂Ge₂ at both RT and LNT, consists of a sequence + - + - of ferromagnetic layers of Mn atoms. The magnetic moment of an Mn atom (≈2μ_B) is parallel to the c-axist. At low temperatures (LHT and lower), the ferromagnetic ordering within the Er sublattice is observed. The magnetic moment (μ_Er ≈ 9μ_B) is perpendicular to the c-axis. From the temperature dependence of the intensities of the magnetic peaks, the following values for the Curie temperatures were obtained: (10±5) K for ErMn₂Si₂ and (8.5±3) K for ErMn₂Ge₂. For ErFe₂Si₂ a collinear antiferromagnetic structure of the + - - + type was found, the magnetic unit cell consisting of the chemical one, doubled along the c-axis.     

Magnetic order in M2Mo3O8 single crystals (M = Mn, Fe, Co, Ni)

Magnetic measurements on hexagonal single crystals of M₂Mo₃O₈ (M = Mn, Fe, Co and Ni) are reported. The Mn compound orders ferrimagnetically at T_c = 41.5 K; the Fe and Co compounds antiferrimagnetically at T_N = 59.5 K and 40.8 K, respectively. No magnetic ordering was found in the Ni compound down to 2 K. All the compounds showed strong magnetic anisotropy when ordered, the results indicating that the magnetic spins' preferred orientation is along the hexagonal axis. Mn₂Mo₃O₈ shows a temperature dependence of the spontaneous magnetization in the ferrimagnetic regime which is rarely observed: as T → 0, M_s → 0.     

Studies on Electronic Structure and Magnetic Properties of an Organic Magnet with Metallic Mn^2＋ and Cu^2＋ Ions

The electronic structure and the magnetic properties of the non-pure organic ferromagnetic compound MnCu(pbaOH)(H2O)3 with pbaOH=2-hydroxy-1, 3-propylenebis (oxamato) are studied by using the density-functional theory with local-spin-density approximation. The density of states, total energy, and the spin magnetic moment are calculated. The calculations reveal that the compound MnCu(pbaOH)(H2O)3 has a stable metal-ferromagnetic ground state, and the spin magnetic moment per molecule is 2.208 μa, and the spin magnetic moment is mainly from Mn ionand Cu ion. An antiferromagnetic order is expected and the antiferromagnetic exchange interaction of d-electrons of Cu and Mn passes through the antiferromagnetic interaction between the adjacent O, 0, and N atoms along the path linking the atoms Cu and Mn.     

催化前驱体亚硝酰硝酸钌中杂质元素的质谱分析

钌催化前驱体是影响负载型钌催化剂催化性能最重要因素。前驱体中的部分杂质会对催化性能产生抑制作用，尤其是S，P，Cl，As等杂质元素含量过高会降低催化剂的活性，严重时会造成催化剂中毒；因此，必须严格控制催化前驱体中杂质元素的含量。建立了快速准确测定催化前驱体亚硝酰硝酸钌（Ru(NO)(NO₃)₃）中杂质元素的分析方法。Ru(NO)(NO₃)₃经稀硝酸溶解后采用电感耦合等离子体串联质谱（ICP-MS/MS）直接测定其中的8个杂质元素（P，S，Ti，V，Cr，Mn，Fe，As）。为防止Ru(NO)(NO₃)₃溶液水解形成Ru(NO)(NO₃)x(OH)_3-x，采用稀硝酸介质有效维持了样品溶液的稳定性。在MS/MS模式下，通过一级四极杆质量过滤器（Q₁）控制进入碰撞/反应池（CRC）的离子，仅允许与待测元素具有相同质荷比（m/z）的离子进入CRC，从而将来自样品基质和等离子气Ar所形成的干扰离子阻止在CRC外，消除了大量质谱干扰。通过向CRC内通入O₂为反应气，目标离子P+，S+，Ti+，V+，As+与O₂的反应为放热过程（31P++O₂→31P16O++O，ΔH_r=-3.17 eV；32S++O₂→32S16O++O，ΔH_r=-0.34 eV；48Ti++O₂→48Ti16O++O，ΔH_r=-1.63 eV；51V++O₂→51V16O++O，ΔH_r=-0.85 eV；75As++O₂→75As16O++O，ΔH_r=-0.63 eV），能自发反应生成氧化物离子；目标离子Cr+，Mn+与O₂的反应为吸热过程（52Cr++ O₂→52Cr16O++O，ΔH_r=+1.38 eV；55Mn++O₂→55Mn16O++O，ΔH_r=+2.15 eV）。为促进Cr+，Mn+与O₂发生反应，通过调整CRC的工作参数，设置八极杆偏置电压为较大的负电压，使Cr+和Mn+在与O₂反应前被加速，提高Cr+和Mn+的动能，促进了反应的发生，通过吸热反应生成氧化物离子；而P+，S+，Ti+，V+，Cr+，Mn+，As+干扰离子在CRC内不能与O₂发生反应，仍然保持原始的m/z。通过二级四极杆质量过滤器（Q₂）将这些干扰离子阻止在外，仅允许所形成的氧化物离子进入检测器，几乎完全消除了元素P，S，Ti，V，Cr，Mn，As的所有质谱干扰。NH₃因含一对孤对电子而具有高反应活性，能与很多金属离子反应形成团簇离子。通过向CRC内通入NH₃/He为反应气，目标离子Fe+与NH₃发生质量转移反应，在所形成多个团簇离子中，Fe(NH₃)+₂的丰度最高且无干扰，通过NH₃质量转移法消除干扰。结果显示，8个元素在0～500 μg·L-1范围内具有良好的线性关系，线性相关系数≥0.999 8。方法的检出限为0.29～485 ng·L-1，按所建立的方法分析了实际样品中8个杂质元素的含量，各元素的加标回收率为93.2%～107.5%，相对标准偏差（RSD）≤3.9%。方法具有样品处理简单、分析速度快和精密度高的特点，适合催化前驱体亚硝酰硝酸钌中多个杂质元素的准确测定，为制备负载型钌催化剂提供了质量保障。     

基于长余辉材料的激光书写和显示

本文给出了长余辉材料一个新的用途,研制了一台以长余辉材料为屏幕的激光书写显示装置,可以人为控制激光笔在余辉材料上随意书写文字、画图并显示.该装置利用单片机和步进电机控制两组轴镜在不同方向的转动,从自己建立的开源矢量图库中调用相关图片,使激光光束在长余辉材料上进行二维矢量的扫描,完成文字书写和绘图显示.用VASP(Vienna abinitio simulation package)软件计算出长余辉材料Mn(H_2PO_4)_2的能级结构,测试了SrAl_2O_4:Eu~(2+),Dy~(3+)和Mn(H_2PO_4)_2的余辉强度衰减曲线,便于调整样机电机的书写速度,测试了Mn(H_2PO_4)_2的反射谱和拉曼谱,其拉曼峰值在625,769和1049 nm及远红外.通过理论和实验研究,掌握了与相应长余辉材料匹配的激发最佳激光波段.制作样机后得到英文、中文、图像的实时书写和显示结果.本装置犹如一只无形的"笔"在纸上挥舞,流畅书写绘画,书写过程配上音乐颇具观赏性,该装置可应用于商业广告显示、动态标语书写、教学投影辅助设备、舞台效果、新型艺术表现形式等领域.     

测量电子自旋——晶格弛豫时间T1的技术问题

本文讨论应用连续波方法测量电子自旋——晶格弛豫时间T₁的实验技术问题。分析液氮翻滚使T₁测量结果很不一致的原因,提出用吹冷气冷冻样品方法,可以解决液氮翻滚对测量T₁所产生的影响.用改进的方法测量ZnS:Mn、Cu粉末样品的T₁,获得重复性较好的实验结果。     

Mn掺杂后三元黄铜矿结构半导体CuInTe2的缺陷特征与热电性能

三元黄铜矿结构(也称类金刚石结构)半导体是一类具有热电转换潜力的新型热电材料. 本次工作中采用电负性更小的Mn元素替换CuInTe₂黄铜矿结构半导体中的Cu元素, 设计制备贫Cu化合物Cu_1-xInMn_xTe₂. 研究表明, 当Mn含量较低时, Mn优先占位在In 位置产生受主缺陷Mn_In^-. 因此随着Mn含量的增大, 载流子浓度和电导率均得到改善. 但当Mn含量进一步增大后, Mn可同时占位在In位置和Cu位置, 除产生受主缺陷Mn_In^-外, 还能产生施主缺陷Mn_Cu⁺. 由于两类极性相反的缺陷之间的湮灭现象, 使得缺陷浓度及载流子浓度开始降低, 晶格结构畸变有变小趋势, 因此在高温下晶格热导率仅略有提高. 研究结果表明, 在某一特定的Mn含量(x=0.05)时, 材料具有最优的热电性能(ZT=0.84@810.0 K), 这一性能约是未掺杂CuInTe₂的2倍.     

Magnetic pair making and breaking effect of Ru in La0.7Sr0.3Mn0.9Ru0.1O3 and La0.5Sr0.5Co0.9Ru0.1O3

The substitutional effect of Ru on the magnetic and transport properties of double exchange ferromagnets, La_0.7Sr_0.3MnO₃ and La_0.5Sr_0.5CoO₃ has been investigated. It is found that substitution of 10% Ru at the Mn site of La_0.7Sr_0.3MnO₃ decreases the Curie temperature by 20 K than that of the parent compound. However, a large decrease in the Curie temperature, ΔT_c80 K and the system undergoes a transition from metallic state to insulating state is observed when 10% Ru is doped in La_0.5Sr_0.5CoO₃. The marginal effect of Ru in the Mn–O–Mn sublattice in comparison to the Co–O–Co sublattice could be due to the magnetic exchange interaction between Mn and Ru by virtue of the fact that Ru exhibits variable valence states, Ru⁺⁴/Ru⁺⁵. The e_g and t_2g parentage of Ru⁺⁵ is similar to Mn⁺⁴ and therefore, Ru⁺⁵ ion appears to participate in the double exchange mediated ferromagnetic (FM) interaction. On the other hand, Ruthenium (IV) ion disrupts an intermediate spin state of cobalt (Co⁺³: t_2g⁵e_g¹), forcing a double exchange FM state to anti-FM state.     

Magnetic properties of Mn-substituted GdCoxMn1−xO3 and LaCoxMn1−xO3

Partial substitution of manganese by cobalt in rare-earth perovskites REMnO₃ leads to unusual magnetic phenomena because of the simultaneous presence of Mn³⁺, Mn⁴⁺, Co²⁺ and Co³⁺ species. The magnetic nature of the RE cation plays a fundamental role in the magnetic properties. We present herein two specific families: for RE=La the magnetic behavior of the |Co+Mn| network is observed, while for Gd its strong magnetic moment interacts with the transition metals, leading to a spin reversal state. Magnetic interactions are maximized at x=0.50, as if two regimes exist: for x<0.5 Co substitutes Mn in the REMnO₃ manganite, and for x>0.5 Mn substitutes Co in the RECoO₃ cobaltite.     

Be,Mg,Mn掺杂CuInO_2形成能的第一性原理研究

研制开发新型的光电材料对促进社会经济发展具有重要的科学意义和实用价值.利用宽禁带CuInO_2铟基材料实现全透明光电材料是目前深入研究的热点.通过基于密度泛函的第一性原理计算方法,本文计算出掺杂元素Mg, Be, Mn在CuInO_2的形成能.计算结果表明,施主类缺陷(如掺杂元素替代Cu原子或进入间隙位置)由于较高的形成能和较深的跃迁能级,很难在CuInO_2材料中出现N型导电;而受主缺陷中,在氧原子化学势极大的情况下, Mg原子替代In能成为CuInO_2理想的受主缺陷.计算结果可为制备性能优异的CuInO_2材料提供指导.