Spin-glass behavior in the antiperovskite manganese nitride Mn3CuN codoped with Ge and Si

Antiperovskite manganese nitrides ${\mathrm{Mn}}_3\left({\mathrm{Cu}}_{0.6}{\mathrm{Si}}_x{\mathrm{Ge}}_{0.4?x}\right)N$ ($x=0.05$, 0.1, 0.15) were prepared and their negative thermal expansion, magnetic and specific heat properties were investigated. A frozen state with a freezing temperature was found at ～207 K in ${\mathrm{Mn}}_3\left({\mathrm{Cu}}_{0.6}{\mathrm{Si}}_{0.15}{\mathrm{Ge}}_{0.25}\right)N$. This indicates that ${\mathrm{Mn}}_3\left({\mathrm{Cu}}_{0.6}{\mathrm{Si}}_{0.15}{\mathrm{Ge}}_{0.25}\right)N$ exhibits a spin glass state at low temperatures. We discussed the cause of spin glass behavior and correlated this spin glass behavior with broadening of the negative thermal expansion operation-temperature window of the manganese nitrides ${\mathrm{Mn}}_3\left({\mathrm{Cu}}_{0.6}{\mathrm{Si}}_{0.15}{\mathrm{Ge}}_{0.25}\right)N$.     

Spin-glass behavior of (La,Gd)B6 alloys

The low-frequency ac magnetic susceptibility of (La_1–x Gd _x )B₆ alloys (0.0035x0.0812) was measured between 0.04 and 10 K in very low and moderate applied magnetic fields up to 8 kOe. In addition, the low-field static susceptibility was measured between 4.2 and 200 K. At low temperatures the alloys exhibit the basic features of the spin glass state, that is sharp maxima and time dependent effects in the low-field ac susceptibility. The temperature and field dependence of the susceptibility follows a law of corresponding states forx0.01, which is characteristic for Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. Effects from interactions between the Gd ions observed above the freezing temperature are consistent with a recent theory based on a virial expansion of the magnetic free energy for the RKKY model and yield |J|=0.04 eV for the magnitude of thes–f exchange integral. The same value is obtained from the initial susceptibility atT0 when compared with a molecular-field result. Above 1 K the initial susceptibility follows a single-impurity Curie law with the free-ion value of the magnetic moment of the Gd solute.     

Spin-glass behavior as a function of concentration and local order by NMR in nearly random NiMn systems

Unidirectional anisotropy fields (H_A) in disordered Ni_{100 ? x}Mn_x (25 ? x ? 32) systems after field cooling are found by NMR (spin echo) to be very sensitive to the Mn concentration and to local order. The H_A increases by roughly a factor of 10 when the concentration increases 5%. The Mn NMR spectra show that all Mn have several first nearest Mn neighbours. For a given concentration, in the above range, the H_A are very sensitive to the annealing-quenching temperatures (T_AQ) and vanish when the sample is cooled down from 900°C in 2 h. The NiMn system can be tuned by heat treatments from spin-glass to a ferromagnet. The Mn NMR spectra with decreasing T_AQ show a clear metallurgical evolution tending to states where a Mn atom sees fewer first nearest Mn neighbours. We find evidence that the anisotropy has its roots in atomic randomness.     

Spin-glass behavior of iron-intercalated zirconium disulfide

The susceptibility of the Fe_0.25ZrS₂ intercalation compound has been shown to depend strongly upon the applied field at lower temperatures. The existence of a cusp at lower fields, together with the fact that the maximum is erased when the sample is field cooled. are attributed to spin-glass properties below 15 K. The 4 K Mössbauer spectrum is magnetic and unresolved, showing a high degree of disorder as far as the spin orientations are concerned. As the temperature is increased, the evolution of the characteristics of the spectra for Fe_0.25ZrS₂, as well as for Fe_0.33ZrS₂, are interpreted in terms of a progressive occurrence of fast relaxing spins. Owing to the non-metallic properties of these compounds, the iron-vacancies disordered distribution and the frustration of the exchange interactions are probably at the origin of such a behavior.     

SrMn0.5Fe0.5O3的自旋玻璃态和过渡金属离子价态的研究

采用固相反应法制备了SrMn_0.5Fe_0.5O₃陶瓷样品,并对样品的晶体结构,磁性和离子价态进行了系统的表征与分析. X射线衍射谱的Rietveld拟合表明样品属于理想的立方钙钛矿型结构,Mn离子和Fe离子随机占据B位的O八面体中心. X射线光电子能谱表明Mn离子为+3和+4的混合原子价态,Fe离子为+3价. 样品在大于230K的高温区域呈现Curie顺磁特性,在小于230 K的低温区域样品表现出自旋玻璃态行为,这种特性源于Mn离子和Fe离子之间的交换作用及自身价态和分布的不均匀性. 由于Fe³⁺离子占据O八面体的中心,对顺磁区的Mssbauer谱测量表现为四级分裂. 关键词： 晶体结构 价态 顺磁 自旋玻璃态     

On the luminescence of manganese(II) phosphates

Luminescent properties of manganese(II) phosphates prepared by thermal dehydration of Mn(H₂PO₄)₂·2H₂O have been studied. The emission spectrum consists of two bands whose relative intensity and spectral position depend on the chemical and crystalline structure of phosphates. The different courses of temperature quenching of luminescence intensity and excitation spectra of each emission band of Mn(H₂PO₄)₂·2H₂O, Mn(H₂PO₄)₂, MnH₂P₂O₇ and c-Mn₂P₄O₁₂ are discussed.     

Cathodic process of manganese (II) in NaCl-KCl melt

In order to achieve the preparation of pure ferromanganese by electrorefining of high-carbon ferromanganese in molten salt, the electrochemical behavior of MnCl₂ was investigated. Molten NaCl-KCl system was selected as the electrolyte, tungsten was used as the working electrode, carbon as the counter electrode, and Ag/AgCl as the reference electrode. The cathodic process was studied by cyclic voltammetry, square wave voltammetry, and chronopotentiometry. The results show that it is a one-step process with 2 electrons transferred. The electrochemical reduction process of Mn²⁺ to Mn was determined as quasi-reversible and diffusion-controlled. Then, galvanostatic electrolysis was carried out to produce manganese metal from NaCl-KCl-MnCl₂ melt, which was characterized by x-ray diffraction (XRD).     

Quantitative analysis of dinuclear manganese(II) EPR spectra

A quantitative method for the analysis of EPR spectra from dinuclear Mn(II) complexes is presented. The complex [(Me(3)TACN)(2)Mn(II)(2)(mu-OAc)(3)]BPh(4) (1) (Me(3)TACN=N, N('),N(")-trimethyl-1,4,7-triazacyclononane; OAc=acetate(1-); BPh(4)=tetraphenylborate(1-)) was studied with EPR spectroscopy at X- and Q-band frequencies, for both perpendicular and parallel polarizations of the microwave field, and with variable temperature (2-50K). Complex 1 is an antiferromagnetically coupled dimer which shows signals from all excited spin manifolds, S=1 to 5. The spectra were simulated with diagonalization of the full spin Hamiltonian which includes the Zeeman and zero-field splittings of the individual manganese sites within the dimer, the exchange and dipolar coupling between the two manganese sites of the dimer, and the nuclear hyperfine coupling for each manganese ion. All possible transitions for all spin manifolds were simulated, with the intensities determined from the calculated probability of each transition. In addition, the non-uniform broadening of all resonances was quantitatively predicted using a lineshape model based on D- and r-strain. As the temperature is increased from 2K, an 11-line hyperfine pattern characteristic of dinuclear Mn(II) is first observed from the S=3 manifold. D- and r-strain are the dominate broadening effects that determine where the hyperfine pattern will be resolved. A single unique parameter set was found to simulate all spectra arising for all temperatures, microwave frequencies, and microwave modes. The simulations are quantitative, allowing for the first time the determination of species concentrations directly from EPR spectra. Thus, this work describes the first method for the quantitative characterization of EPR spectra of dinuclear manganese centers in model complexes and proteins. The exchange coupling parameter J for complex 1 was determined (J=-1.5+/-0.3 cm(-1); H(ex)=-2JS(1).S(2)) and found to be in agreement with a previous determination from magnetization. The phenomenon of exchange striction was found to be insignificant for 1.     

Electron spin relaxation in solutions of manganese (II) ions

Measurements of the neutron scattering static structure factor S(Q) are reported for orthobaric liquid fluorine at 77K for an incident wavelength of 1·2Å. The observed S(Q) and the atom-atom correlation function are discussed and compared with those of other halogens and oxygen. From the d(r) pair distribution function it is shown that liquid fluorine has a coordination number of first neighbours more similar to liquid oxygen than halogens. The number of atoms in the first and second coordination shell is in good agreement with a close-packed arrangement of atoms.     

Spin-glass transition in a Kondo lattice with quenched disorder

We use the Popov-Fedotov representation of spin operators to construct an effective action for a Kondo lattice model with quenched disorder at finite temperatures. We study the competition between the Kondo effect and frozen spin order in Ising-like spin glass. We present the derivation of new mean-field equations for the spin-glass order parameter and analyze the effects of screening of localized spins by conduction electrons on the spin-glass phase transition.     

2-μm fluorescence and Raman spectra in high and low Al(PO3)3 content fluorophosphates glasses doped with Er-Tm-Ho

Thermal stability and 2-μm fluorescence of high and low Al(PO_3)_3 content of fluorophosphate glasses are investigated.Thermal stability of high Al(PO_3)_3 content of fluorophosphate glass is better than low Al(PO_3)_3 content of fluorophosphate glass.However, 2.04-μm fluorescence intensity of high Al(PO_3)_3 content of fluorophosphate glass is only 48.2, lower than low Al(PO_3)_3 content of fluorophosphate glass.Raman spectroscopy is employed to investigate the difference in thermal stability and 2-μm fluorescence.Moreover, fluorescence peak intensity ratios of 2.04 to 1.81 μm and 2.04 to 1.57 μm are calculated, which indicate that Er-Tm-Ho doped fluorophosphate glasses are suitable materials in 2-μm applications.     

Electromigration of gold (high concentration) in lead

The steady state method was used to study the electromigration of ¹⁹⁵Au in lead doped with 680 ppm Au. In the temperature range 165–270°C Au migrates toward the anode, as in the case of more dilute solutions; but the effective charge increases in magnitude with decreasing temperature at a faster rate than that observed for dilute Pb(Au) samples, so that the difference between the effective charge for the 680 ppm samples and that for dilute samples becomes larger as the solubility limit is approached. A simple model, which allows for formation of Au doublets in equilibrium with the singlets, predicts an apparent increase of Z¹ with concentration of impurity at lower temperatures somewhat greater than the observed effect.     

Vibrational spectroscopic investigation of the hydrates of manganese(II) oxalate

The three known hydrates of manganese(II) oxalate, α‐MnC₂O₄ · 2H₂O, γ‐MnC₂O₄ · 2H₂O and MnC₂O₄ · 3H₂O were synthesized by known procedures and characterized by X‐ray powder diffractometry. Their infrared (IR) and Raman spectra were recorded and discussed on the basis of its structural peculiarities allowing to establish some interesting relations between them and with other, previously investigated, oxalate complexes. The IR spectra of partially deuterated samples of α‐MnC₂O₄ · 2H₂O were also discussed, reinforcing some of the performed assignments. Copyright © 2009 John Wiley & Sons, Ltd.     

Electron paramagnetic relaxation in aqueous solutions of manganese (II) ions

The processes of the electron paramagnetic relaxation, molecular motions and structural changes in aqueous solutions of manganese nitrate have been investigated by direct measurement of spin-lattice (T ₁) and spin-spin (T ₂) relaxation times for a wide range of concentrations, temperatures and viscosities. T ₁ and T ₂ were measured by a non-resonance absorption method.

It was discovered that some structural regions exist at the different concentrations of Mn(II) ions in solution. So, the structure of highly concentrated solutions may be considered as one of the corresponding crystallohydrate. The structural microinhomogeneities were observed also in the intermediate concentration range at definite temperatures. It is shown that the relaxation mechanism proposed by Bloembergen and Morgan is not effective in the concentration range studied by us.

The analysis of relaxation times and E.P.R. spectra has shown the formation of ‘liquid microphases’ at the freezing point of the solution. Such microphases can exist at temperatures a few tenths of a degree below the solvent freezing point, and its composition considerably differs from the initial solution.

The correlation times for intramolecular and intermolecular electron relaxation mechanisms are evaluated and their nature is discussed.     

Spin-glass-like behavior in a Fe-Zr amorphous alloy

The thermomagnetization curves and the hyteresis loops of the amorphous alloy Fe₉₂Zr₈ at low temperature have been investigated. Spin-glass-like behavior such as a thermomagnetic history and relaxation of remanence has been observed.     

Antiferromagnetic interaction in dichlorobis (pyrazole) manganese (II); three independent determinations

The value of the antiferromagnetic interaction in the supposed linear chain compound, Mn(pyrazole)₂Cl₂, has been determined with the aid of low-temperature susceptibility and specific heat measurements, and paramagnetic resonance linewidth studies. The results of the measurements are consistent with each other and yield a $\text{J}\text{k}$ value of ?0.85 ± 0.05 K.     

Critical behavior in the amorphous Ising ferromagnet with a random field

Within the differential operator method and the effective-field approximation, the critical behaviour of the amorphous Ising ferromagnet with a random field is studied. Tricritical points and reentrant phenomena are discussed. The influence of the random field and the amorphization on the transition temperature is also investigated.