Angular dependence of the superexchange interaction Fe3+-O2−-Cr3+

The super-exchange interaction parametersI(Fe, Cr) of Fe³⁺ and Cr³⁺ in iron doped rate-earth orthochromitesRCr_0.99Fe_0.01 O₃ (R=La, La_0.5Nd_0.5, Nd, Sm, Gd, Dy, Y, Er, Yb or Lu) have been obtained from⁵⁷Fe magnetic hyperfine structure measurementsvia the Mössbauer effect.The dependence of the experimental valuesI(Fe, Cr) on the Fe–O–Cr average superexchange angle (depending upon the relative size of the rare-earth (RE) ionR ³⁺) is well described by the equationI(d⁵, d ^N ) = _N + _N cos + _N cos² .Within the accessible range of super-exchange angles 142°156°, the Fe³⁺–O^2––Cr³⁺ interaction is negative (antiferromagnetic). However, a theoretical analysis predicts a sign reversal forI(Fe, Cr.) at about 162° and thus ferromagnetic character of the interaction between 162° and 180°.The spin-only super-exchange interaction integrals fore _g andt _2g electrons, separately, are also calculated. Their angular dependence is accounted for by the behaviour of the antiferromagnetic kinetic and ferromagnetic potential exchange which are of different character when passing from 180° to 90° super-exchange geometry. The magnitude and the sign of the spin-only super-exchange integral for an arbitrary 3d cation, pair is predicted.     

Influence of the Fe3+ –for – Al3+ Octahedral Substitutions on the IR Spectra of Montmorillonite Minerals

Abstract

The influence of octahedral replacement of Al³⁺ by Fe³⁺ on the infrared spectra of montmorillonites in the domain of OH vibrations is presented.

The obtained results suggest that in the domain of OH-bending vibration, the absorption band from 870 cm^?1 (Al³⁺ -OH-Fe³⁺) can not be detected in the spectra of montmorillonites when the octahedral Fe³⁺ content is below 0.10-0.15 (per half unit cell)

In the domain of OH-stretchtng, the increasing Fe³⁺ -for-Al³⁺ substitution in the dioctahedral series of smectites causes a continous shift of the absorption band ascribed to M³⁺ - OH - M³⁺ vibrations to lower frequencies.     

偏最小二乘分光光度法同时测定Fe3+和Al3+

以铬天青S(CAS)为显色剂,溴化十六烷基三甲胺(CTMAB)作为增溶增敏剂及丙酮作为稳定剂,采用偏最小二乘(PLS)分光光度法对Fe3 和Al3 同时测定。综合考虑光源稳定性,双组分吸光度加和性及线性等因素,选取6 10～6 70nm范围内7个波长以供多波长数据采集。作为比较,在后续数据分析中分别采用了CPA矩阵法和偏最小二乘法(PLS) ,结果表明后者具有明显的优势。     

Diffusion mechanisms in the Fe3Si alloys

In this paper,the possible reascon for the high thermal vacancy concentration and the low migration barriers for the Fe atorn diffusion in the stoichiometric DO3 structure Fe3Si have been discussed.The high thermal vacancy conenrrarion was attributed to the compression of Fe-Fe atcmic pairs and the tension of Fe-Si atomic pairs in Fe75Si25.The deformations (compression or tensicn)of the atompairs incrcase the interatomic potentials and thus dercrease the enthalpies of vacancy formation.The low minration bamiers for the Fe atom diffusion in Fe75Si25 were related to the symmetric property of the triangualar bamiers.Additionally.it was considered that the Si atoms in Fe3Si could probably migrate via nearest-neighbour jumps without disturbing the long-range order of atomic arrangements,provided that during the diffusion process the residence time on the antistructure sites is very short.     

KZnF3:Fe3+体系局域晶体结构的理论研究

本文采用对角化三角场中d5组态完全能量矩阵的方法,研究了KZnF3Fe3+体系的局域晶体结构和EPR参量之间的关系.在分析中我们引入了双层配位模型,即配位体包括Fe3+离子最近邻的6个F-离子和次近邻的8个K+离子.计算表明KZnF3Fe3+的局域结构畸变源于一个K+离子沿C3轴方向(即[111]方向)向Fe3+离子的移动,从而诱导F-离子的位移,使得Fe3+-F-键与C3轴夹角发生变化.通过计算EPR的低对称参量D和(a-F),我们分别得出室温(T=300K)时的畸变角为△θ1=2.58°,△θ2=-1.4°和低温(T7=77 K)时畸变角为△θ1=2.85°,△θ2=-1.40计算结果与实验观察值△θ1=2.8±0.3°,△θ2=-1.1±0.3°相符合.     

姜黄素分光光度法测定马林果中Fe3+

本文通过分光光度法研究了姜黄素与Fe3 的显色反应,发现其络合物的最大吸收波长为530nm,摩尔吸光系数为ε530=1.8×105L/mol.cm.校准曲线的回归方程为y=0.0353 0.3075x,r=0.9898.Fe3 含量在0.4-1.2μg/mL范围内有很好的线性关系.在pH=l1.8介质中姜黄素与Fe3 形成1:1的络合物,并且其稳定,方法的选择性好,用于各种水果中铁的测定,可得到满意的结果.     

Using the 57m Fe3+ Mössbauer probe to determine the EFG tensor parameters at CuO cation sites

Mössbauer emission spectroscopy of the ⁵⁷Co(^57m Fe) isotope has shown that the impurity iron atoms appearing at the CuO-lattice cation sites after the decay of ⁵⁷Co²⁺ are donors and can become stabilized in two charge states, ^57m Fe³⁺ and ^57m Fe²⁺, and that the population ratio of these states depends on the Fermi level, whose position is governed by native CuO-lattice defects. A satisfactory agreement between the calculated and experimental values of the quadrupole splitting in Mössbauer spectra has been obtained for the ^57m Fe³⁺ centers. This permits one to consider the results obtained in the ⁵⁷Co(^57m Fe) Mössbauer emission spectroscopy study of cuprates as reliable experimental data on the crystal-field EFG tensor parameters at copper sites.     

常温下YGaG:Fe3+体系的EPR谱研究

本文采用对角化三角晶场中d5组态离子的完全能量矩阵的方法,研究了YGaG:Fe3 体系的EPR谱与局域晶格畸变的关系,利用EPR谱的低对称参量D和(a-F)的实验值确定出Fe3 离子在YGaG:Fe3 体系中的键长R=0.2005 nm,键角θ=51.498°,以及晶格畸变角Δθ=0.954°。     

ZnO:Fe3+体系局域晶格结构的研究

本文采用对角化三角场中d5组态离子的完全能量矩阵的方法,研究了Fe3+离子在ZnO:Fe3+体系的局域结构与EPR参量的关系,结果表明：在ZnO:Fe3+体系中,Fe3+取代了Zn2+离子后整个晶体显示出压缩畸变,其畸变参量ΔR=-0.119A和Δθ=0.339°被确定。     

A microscopic model for the spin-spin relaxation of Fe3+ in an amorphous Mössbauer sample

A model for the spin-spin relaxation of glassy paramagnetic substances in external magnetic fields is developed and applied to frozen aqueous solutions of Fe(NO₃)₃. In these the ferric ions are surrounded by weakly distorted octahedral complexes of water molecules. The relaxation process is characterized by several relaxation frequencies which replace the single flip frequency of earlier approaches. In contrast to the latter, they can be calculated from the microscopic properties of the sample. The only model parameter is the ligand field coupling constant D determining the relaxational behavior. A set of Mössbauer spectra, measured under various experimental conditions, is well described by a single value of the ligand field parameter D = 2.2g_B kG. Some characteristic features of the model become obvious in the spectra, e.g. the fading of certain absorption lines with increasing Fe³⁺ concentration.     

基于三苯胺的增强型Fe3+荧光探针及性能

Fe3+在人的许多生理过程中扮演着重要的角色,例如氧气运输、DNA合成、髓磷脂合成、线粒体呼吸、神经递质合成和代谢等.然而,过量的Fe3+会诱导细胞产生·OH从而引起细胞损伤,并且还会诱导β-地中海贫血、帕金森病、癫痫和阿尔茨海默病等疾病的发生.因此,对Fe3+的检测和监测具有非常重要的意义.本文设计并合成了一种以三苯...     

The Comparison of the Holographic Storage Properties of Fe∶LiNbO_3 and Fe∶Ce∶LiNbO_3 Crystals

１ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｔｈｅｐｒｅｓｅｎｔ，ｔｈｅｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｍａｔｅｒｉａｌｓａｒｅｗｉｄｅｌｙｕｓｅｄｆｏｒｈｉｇｈｄｅｎｓｉｔｙｈｏｌｏｇｒａｐｈｉｃｓｔｏｒａｇｅ．Ａｓｏｎｅｏｆｔｈｅｍｏｓｔｐｏｐｕｌａｒｐｈｏｔ...     

Relaxation phenomena in Cr3+ doped Al2O3−Fe 2 57 O3 systems

Mössbauer absorption spectra have been measured for Cr³⁺ doped Al₂O₃?Fe ₂ ⁵⁷ O₃ systems for different values of the Cr³⁺ concentration at room temperature. The cross relaxation between Fe³⁺ and Cr³⁺ ions, which destroys the paramagnetic hyperfine structure of Fe⁵⁷ observed in undoped Al₂O₃?Fe ₂ ⁵⁷ O₃, is thoroughly studied. The experimental results suggest a new kind of cross-relaxation process involving three spins, i.e. two Fe³⁺.ions and one Cr³⁺. The process, though it is a higher-order one, is highly effective because it is energy-conserving.     

Al2O3:Fe3+体系晶格局域结构的EPR理论研究

本文通过分析Al2O3∶Fe3+体系中Fe3+离子的EPR谱,研究Fe3+的局域晶体结构结果表明Al2O3∶Fe3+的局域结构存在各向异性膨胀.用拟合EPR谱的低对称参量D和(a-F)实验值的方法,求得两个三棱锥的棱与C3轴的夹角分别为θ1=46.54°和θ2=61.26°,相对于原Al2O3结构的畸变角分别是Δθ1=-1.1°±0.1°,Δθ2=-1.8°.两畸变角同时均小于0说明Al2O3∶Fe3+体系中含Fe3+离子的晶格主要产生沿C3轴的伸长畸变.     

Fe∶LiNbO3全息图热定影及H+浓度的影响

应用光折变效应动力学方程,导出了在Fe∶LiNbO3中对光折变全息图热定影所需的最小H+浓度,以及H+浓度与光栅空间频率的关系.应用光谱比较法测量了不同样品的H+浓度值.得出了进行有效热定影的H+浓度范围.完成了Fe∶LiNbO3全息存储和热定影实验.获得了100 h连续无损读出的良好热定影实验结果.     

μ+SR study of Ising spin-glass Fe0.5Mn0.5TiO3

A typical Ising spin-glass Fe_0.5Mn_0.5TiO₃ has been investigated by ⁺ spin relaxation measurements. It is found that the local magnetic fields at the ⁺ stopping sites appear at a temperature twice as high asT _SG. The directional distribution of the local magnetic fields is nearly isotropic, indicating the existence of the transverse spin components. It is clearly demonstrated that the spins fluctuate belowT _SG and even at 4 K. Taking into account the results obtained by other methods, the main part of the fluctuations is inferred to be due to the transverse spin components and the fluctuation limes at 4 K are driven into a range between 10^–5 and 10^–7 s.     

Mössbauer Study of the Fe3B/Nd2Fe14B Nanocomposite Magnet by the Addition of Co

The addition of Co to Nd₄Fe_77.5–x Co _x Hf_0.5Ga_0.5B_18.5 (0x5) was found to enhance the magnetic properties of Fe₃B/Nd₂Fe₁₄B nanocomposite magnets. The enhancement resulted from the fact that Co tends to retard the formation of Fe₃B from the amorphous matrix but to accelerate that of Nd₂Fe₁₄B. The decreased interval between the crystallization temperature of Fe₃B and Nd₂Fe₁₄B led to a uniform grain size distribution of both phases during the annealing treatment. The additive Co was confirmed to partition mainly to Nd₂Fe₁₄B crystals rather than to Fe₃B which was traced by XRD and Mössbauer spectroscopy as well. About 72 vol.% of Fe₃B, 27 vol.% of Nd₂Fe₁₄B, and a small amount of Fe around 1 vol.%, respectively, were found to form. However, the volume fraction of each phase did not vary by the addition of Co up to 5 at.%.