Structure and magnetic properties of a new single-molecule magnet [Mn11Fe1O12 (CH3COO)16(H2O)4].2CH3COOH.4H2O

A new single-molecule magnet [Mn₁₁Fe₁O₁₂ (CH₃COO)₁₆(H₂O)₄]?2CH₃COOH?4H₂O (Mn₁₁Fe₁) has been synthesized.The structure has been studied by the single crystal x-ray diffraction. The difference of Jahn--Teller distortion between Fe³⁺ and Mn³⁺ ion reveals that Fe³⁺ ion substitutes for Mn³⁺ ion on the Mn(3) sites in the Mn₁₂ skeleton. The temperature dependence of the magnetization gives a blocking temperature T_B=1.9K for Mn₁₁Fe₁. Based on the magnetization process analysis of the crystal at T=2K, we suggest that Mn₁₁Fe₁ has the ground state with a total spin S= 11/2.     

Magnetic properties of the compounds N(CH3)4MnIIMIII(CN)6 ·8 H2O(MIII = Mn,Fe)

In the isostructural cyanobridged chain compounds N(CH₃)₄Mn^IIM^III(CN)₆ · 8H₂O high spin Mn(II) ions couple antiferromagnetically to low spin Mn(III) of Fe(III) ions. The Mn^II–Mn^III compound orders ferrimagnetically below T_N = 28.5 ± 1 K. The tetragonal a and b axes are easy ones for the magnetic moments. In the Mn^II–Fe^III compound antiferromagnetic order occurs below T_N = 9.3 K, with spins aligned along the tetragonal c axis. The compound undergoes a meta-magnetic transition from the antiferromagnetic to a ferrimagnetic phase. This occurs at 2 K for a field H_crit ≈ 1.2 T. The temperature dependence of H_crit, which vanishes at T_N, is followed. The tricritical temperature T¹ is ～ 5 K.     

Preparation and magnetic properties of Mn12 clusters with 4-cyanobenzenecarboxylate ligand, [Mn12O12(O2CC6H4-p-CN)16(H2O)4] and its tetraphenylphosphonium salts

The new Mn₁₂ magnetic clusters with 4-cyanobenzenecarboxylate ligand, [Mn₁₂O₁₂(O₂CC₆H₄-p-CN)₁₆(H₂O)₄] (1) and its singly (2) and doubly (3) reduced analogs as their tetraphenylphosphonium salts, have been synthesized and characterized by elemental analyses, Raman, ESI-MS spectra and magnetic measurements with a SQUID magnetometer. Unlike the known Mn₁₂ oxocarboxylate clusters, which are very soluble in CH₃CN or CH₂Cl₂, the complex 1 is not dissolved in organic solvents providing an indication for strong intermolecular interactions which lead to strong dipole–dipole interactions between clusters and affect the magnetic behavior. The one-electron and two-electron reduced clusters (2, 3) contain the bulk counterion and dissolve in CH₃CN. They show magnetic properties characteristic for anion Mn₁₂ single-molecule magnets.     

Preferential ordering of Mn and Fe Atoms in Y6(Fe1−xMnx)23

Neutron diffraction studies of the nomagnetic compositional range of the Y₆(Fe_1?xMn_x)₂₃ system reveal the presence of preferential ordering of Fe and Mn atoms on the four transition metal crystallographic sites. Throughout the entire compositional range of the ternary system, Mn atoms prefer to occupy the f₂ site and Fe atoms the f₁ site. Refinements of the data were carried out using the Rietveld profile method.     

Effect of Mn doping on electrochemical properties of Li2FeSiO4/C cathode materials based on a vacuum solid-state method

Li₂Fe_1?x Mn _x SiO₄/C (x?=?0, 0.1, 0.2, 0.3, 0.4, 0.5) are prepared by a vacuum solid-state reaction of SiO₂, CH₃COOLi·2H₂O, FeC₂O₄·2H₂O, and Mn(CH₃COO)₂·4H₂O. The crystalline structures, morphologies, and electrochemical performances are analyzed contrastively by X-ray diffraction (XRD), scanning electron microscopy, galvanostatic charging–discharging, and electrochemical impedance spectroscopy (EIS). The XRD and EIS results prove that Mn doping may be beneficial to the battery performances of Li₂FeSiO₄ materials, by reducing the crystallite sizes, decreasing transfer impedance (R _ct), and increasing Li-ion diffusion coefficient (D _Li+). However, the galvanostatic charge–discharge results indicate that only Li₂Fe_0.8Mn_0.2SiO₄/C shows the improved performance; its initial discharge capacity can reach to 190.7 mAh g^?1. All things considered, the increased impurities after Mn doping, decided by reference intensity ratio (RIR) method, seem to impose more negative effects on the Li₂Fe_1?x Mn _x SiO₄/C performances. Under this premises, the Mn-doped content is particularly important for Li₂FeSiO₄ materials prepared by the vacuum solid-state method.     

Ab-initio calculation of electronic structure of partially inverted manganese ferrite

Electronic structure of manganese ferrite is calculated using the density functional theory. Partially inverted structure with the inversion parameter y=0.0625 is considered, using four different supercells (Mn₁₅Fe)_A[Fe₃₁Mn]_BO₆₄ that differ in relative position of Fe_A and Mn_B. The crystal structure was optimized by minimizing the forces acting on the atoms. The spin magnetic moments m of Mn and Fe ions depend to some extent on their position in the supercell, but we found that in all cases m(Mn_B) is considerably smaller (by approx. one Bohr magneton) than m(Mn_A). This indicates strongly that the formal valence of Mn_B is 3+. Trivalent manganese in an octahedral position is expected to exhibit a Jahn–Teller effect and corresponding analysis was performed. No pronounced localization of the extra electron in the octahedral sublattice that would represent the Fe²⁺ ion was found.     

Measurement of mass attenuation coefficients in some Cr,Co and Fe compounds around the absorption edge and the validity of the mixture rule

The total mass attenuation coefficients for elements Cr, Co and Fe and compounds CrCl₂, CrCl₃, Cr₂(SO₄)₃K₂SO₄·24H₂O, CoO, CoCl₂, Co(CH₃COO)₂, FePO₄, FeCl₃·6H₂O, Fe(SO₄)₂NH₄·12H₂O were measured at different energies between 4.508 and 14.142 keV using secondary excitation method. Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr were chosen as secondary exciters. 59.5 keV γ-rays emitted from a ²⁴¹Am annular source were used to excite a secondary exciter and K_α(K-L₃, L₂) lines emitted by the secondary exciter were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. It was observed that mixture rule method is not a suitable method for determination of the mass attenuation coefficients of compounds, especially at an energy that is near the absorption edge. The obtained values were compared with theoretical values.      

二硫酸-二元胺锰和二羟基-二元胺锰纳米片磁性的第一性原理研究

We perform first-principles simulations on a type of two-dimensional metal-organic nanosheet derived from the recently reported manganese bis-dithiolene Mn₃C₁₂S₁₂ [Nanoscale 5, 10404 (2013)] and manganese bis-diamine Mn₃C₁₂N₁₂H₁₂ [ChemPhysChem 16, 614 (2015)] mono-layers. By coordinating chalcogen (S or O) atoms and -NH- group to Mn atoms with trans- or cis-structures and preserving space inversion symmetry, four configurations of this type of nanosheet are obtained: trans-manganese dithiolene-diamine Mn₃(C₆S₃N₃H₃)₂, cis- manganese dithiolene-diamine Mn₃(C₆S₆)(C₆N₆H₆), trans-manganese dihydroxyl-diamine Mn₃(C₆O₃N₃H₃)₂, and cis-manganese dihydroxyl-diamine Mn₃(C₆O₆)(C₆N₆H₆). The ge- ometric con guration, electronic structure and magnetic properties of these metal-organic nanosheets are systematically explored by density functional theory calculations. The cal- culated results show that Mn₃(C₆S₃N₃H₃)₂, Mn₃(C₆O₃N₃H₃)₂ and Mn₃(C₆O₆)(C₆N₆H₆) monolayers exhibit half-metallicity and display strong ferromagnetism with Curie transition temperatures near and even beyond room temperature, and Mn₃(C₆S₆)(C₆N₆H₆) monolayer is a semiconductor with small energy gap and spin frustration ground state. The mechanisms for the above properties, especially in uences of diflerent groups (atoms) substitution and coordination style on the magnetism of the nanosheet, are also discussed. The predicted two-dimensional metal-organic nanosheets have great promise for the future spintronics ap-plications.     

The first observation of photoinduced tuning of AC magnetization for organic–inorganic hybrid materials composed of Mn12-acetate and azobenzene

New organic–inorganic hybrid material composed of typical single-molecule magnet [Mn₁₂(CH₃COO)₁₆(H₂O)₄O₁₂]·2CH₃COOH·4H₂O (Mn₁₂-acetate) and photochromic azobenzene in PMMA cast films was prepared to observe novel photomagnetic phenomenon. We characterized it by means of UV–visible absorption and IR spectra to confirm photoisomerization of azobenzene even at room temperature. We measured temperature and field dependence of DC susceptibility, and temperature and frequency dependence of AC susceptibility as comparing with bulk precipitates of Mn₁₂-acetate. We found some differences in hysteresis loops for them. After alternate illumination of UV or visible light for 3 min at 3 K, we could observe reversible decrease or increase of in-phase AC susceptibility (and little changes of DC susceptibility) for the hybrid materials accompanying cis–trans photoisomerization of azobenzene.     

First-principles study on the electronic structure and the ferromagnetic properties of the cyano-bridged bimetallic compound Mn2(H2O)5Mo(CN)7·4H2O (α phase)

First-principles calculations have been performed to study the electronic structure and the ferromagnetic properties of the cyano-bridged bimetallic compound Mn₂(H₂O)₅Mo(CN)₇·4H₂O (α phase).The calculations were based on density-functional theory and the full potential linearized augmented plane wave method (FP-LAPW). The calculated total energies revealed that the compound has a stable ferromagnetic (FM) ground state, which is in agreement with the experiments. The electronic structure of the compound has a half-metallic behavior. The calculated magnetic moment per molecule is about 15.000 μ_B, the magnetic moment are mainly from Mo and Mn atoms with d electronic configuration. It is also found that there exists ferromagnetic interaction between low-spin Mo²⁺ and high-spin Mn³⁺ ions through the Mo-C-N-Mn linear linkages.     

The Mössbauer study of Nd−Fe−Co−B permanent magnetic alloys

Sintered Nd₁₇ (Fe_1?x Co_x)₇₅B₈ permanent magnetic alloys have been studied by Mössbauer effect, X-ray diffraction and electron probe micro-analysis, The results show that the alloys are composed of the tetragonal phase Nd₂(Fe,Co)₁₄B, the B-rich phase Nd₁₁₁(Fe,Co)₄B₄ and the Nd-rich phase Nd₈₀(Fe,Co)₁₉B. In the tetragonal phase, Co atoms occupy preferentially the k₂ and j₂ sites, and Fe atoms occupy randomly the k₁ site and preferentially the j₁ site while the e and c sites seem to be completely occupied by Fe atoms.     

The tuning of quantum magnetization for organic/inorganic hybrid materials composed of Mn12-acetate and azobenzene casted into PMMA films on PVA films

In order to examine the effects of polymer matrix substituting crystalline solvents and photoisomerization of azobenzene in photo-modulation of AC susceptibility discovered recently, we have compared various quantum magnetic properties of new organic/inorganic hybrid materials composed of Mn₁₂-acetate (a typical single-molecule magnet, [Mn₁₂(CH₃COO)₁₆(H₂O)₄O₁₂]·2CH₃COOH·4H₂O) containing or not containing azobenzene casted into polymethylmethacrylate (PMMA) films on Polyvinylalchol (PVA) films. The M-H hysteresis loops below blocking temperature for both materials exhibited distinct differences of the dM/dH vs. H plots, which suggested azobenzene as well as crystalline solvents resulted in tuning of magnetic properties. Moreover, the AC susceptibility at 0.1-1000 Hz frequencies provided activation energy U_eff=87 K from Arrhenius law for both materials, albeit Cole-Cole plots indicated perturbation of quantum magnetization for both hybrid materials in polymer matrix.     

TbyDy1-y(Fe1-xTx)2(T=Al,Mn)的磁致伸缩与内禀磁致伸缩特性

用直拉单晶生长系统制备Tb_yDy_1-x(Fe_1-xT_x)₂(T=Al,Mn)单晶,并测量其磁致伸缩.用电弧炉合成多晶Tb_yDy_1-y(Fe_1-xT_x)₂(T=Al,Mn),并用X射线衍射方法测量拟合得到内禀磁致伸缩.结果表明,Al和Mn替代后饱和磁场降低,说明Al和Mn的替代明显地降低了各向异性能.随Al和Mn替代量的增加,总的趋势是材料的内禀磁致伸缩λ₁₁₁降低.对Tb_0.5Dy_0.5(Fe_0.9Mn_0.1)₂单晶,在不加压情况下的磁致伸缩效果并不明显,但当施加压力时,磁致伸缩变化显著,尤其在12—26MPa压力下,磁致伸缩变化很大,且低场效果很好. 关键词：     

Nd2(Fe1-xMnx)14B的低温内禀矫顽力

当x<0.5时,Nd₂(Fe_1-xMn_x)₁₄B可形成四方晶体结构,空间群为P4₂/mnm。在低温下,该赝三元化合物的大块铸态样品具有高矫顽力。此矫顽力不依赖于热处理等工艺过程,因此具有内禀性质。内禀矫顽力 _iH_c与样品的成分有关。Nd₂(Fe_1-xMn_x)₁₄B的起始磁化曲线具有传播场H_p,并且H_p的数值与 _iH_c接近。这表明内禀矫顽力是由畴壁钉扎造成的。研究了 _iH_c与温度的变化关系,并估算了钉扎位垒的强度。测量了Nd₂(Fe_1-xMn_x)₁₄B的居里温度和饱和磁化强度。在此赝三元化合物中,交换作用随Mn对Fe的替换而急剧降低。这使得畴壁厚度变窄。Nd₂(Fe_1-xMn_x)₁₄B的磁化和反磁化行为可用窄畴壁的特征来解释。 关键词：     

Mössbauer study on characterization of Co[Fe(CN)5NH3 \cdot x H2O

The electronic states of Fe atoms in Co[Fe(CN)₅NH₃ H₂O were studied by means of ⁵⁷Fe Mössbauer spectroscopy. The Mössbauer spectra of Co[Fe(CN)₅NH₃ 6H₂O show the coexistence of mixed valences for the Fe atoms and a magnetic relaxation at 4 K. When water molecules were removed, electron transfer from Co to Fe occurred.     

Emission Mössbauer spectroscopic studies of57Fe atoms produced in57Co-labelled trinuclear cobalt-iron halogenoacetate complexes

Mixed-valence states of⁵⁷Fe atoms produced after EC-decay of⁵⁷Co in a series of trinuclear cobalt-iron halogenoacetate complexes, [Co^IIFe ₂ ^III O(CH_3?nX_nCO₂)₆(H₂O)₃] (0≤n≤3, X=Cl, Br, and I), were studied by comparing the results obtained by emission Mössbauer spectroscopy with those observed in absorption Mössbauer spectra of analogous trinuclear iron complexes, [Fe^IIFe ₂ ^III O(CH_3?nX_nCO₂)₆(H₂O)₃]. Some of the emission Mössbauer spectra show a temperature-dependent mixed-valence state as found in the absorption Mössbauer spectra. Others show a somewhat different temperature dependence compared with the absorption Mössbauer spectra. The results were interpreted in terms of after-effects of the EC-decay.     

Mössbauer and molecular orbital (MO) study of localized and delocalized mixed-valence organo-FeIIFeI bisandwiches

A Mössbauer study of two mixed-valence Fe^IIFe^I compounds C₅H₅Fe(C₅H₄)₂ FeC₆(CH₃)₆ (1) and ¦C₆(CH₃)₆ Fe(C₅H₄)₂ Fe C₆(CH₃)₆¦⁺ (2 ⁺) was carried out from 4.2K to room temperature. Zero-field spectra show two types of iron atoms for1 and one type for2 ⁺. Hence1 is a localized mixed-valence complex and2 ⁺ a delocalized mixed-valence complexe. High magnetic field spectra for 2⁺ give a negative sign for the EFG and show the valence electron is delocalized on the two centers. IEHT-MO calculations confirm the results and allow to explain the temperature independence of the quadrupole splitting (QS) of2 ⁺.     

Chemical shifts of Cr Kα and Kβ1, 3 lines by WDXRF spectrometry

Chemical shift and full widths at half maximum (FWHM) intensity of chromium Kα and Kβ_{1, 3} lines were examined for 12 kinds of materials containing chromium (CH₃CO₂)₇Cr₃(OH)₂, CrK(SO₄)₂.12H₂O, Cr(NO3)₃.9H₂O, Cr₂O₃, CrF₂, CrF₃.4H₂O, CrCl₂, CrCl₃, CrCl₃.6H₂O, [CrCl₂(H₂O)₄]Cl.2H₂O, Cr₂(SO₄)₃.15H₂O, CrO and Cr metal by wavelength‐dispersive X‐ray fluorescence (WDXRF) spectrometry. The chemical shifts, asymmetry index and the half‐widths of both the X‐ray emission lines show interesting trends with the oxidation state of chromium. It was observed that the chemical shifts for F compounds are higher than Cl compounds. It was also found larger chemical shifts and FWHM for Kβ_{1, 3} lines than Kα ones. It should be noted that the magnitude of chemical shifts increases with increase in the number of ligand atoms. Copyright © 2009 John Wiley & Sons, Ltd.     

Micro‐Raman investigation of transition‐metal‐doped ZnO nanoparticles

We measured the Raman spectra of ZnO nanoparticles (ZnO‐NPs), as well as transition‐metal‐doped (5% Mn(II), Fe(II) or Co(II)) ZnO nanoparticles, with an average size of 9 nm. A typical Raman peak at 436 cm⁻¹ is observed in the ZnO‐NPs, whereas Zn_1−xMn_xO, Zn_1−xFe_xO and Zn_1−xCo_xO presented characteristic peaks at 661, 665 and 675 cm⁻¹, respectively. These peaks can be related to the formation of Mn₃O₄, Fe₃O₄ and Co₃O₄ species in the doped ZnO‐NPs. Moreover, these samples were analyzed at various laser powers. Here, we observed new vibrational modes (512, 571 and 528 cm⁻¹), which are specific to Mn, Fe and Co dopants, respectively, and ZnO‐NPs did not reveal any additional modes. The new peaks were interpreted either as disorder activated phonon modes or as local vibrations of Mn‐, Fe‐ and Co‐related complexes in ZnO. Copyright © 2007 John Wiley & Sons, Ltd.