Electronic structure of 3d-metal monosulphides by the xα discrete variational method

Electronic structure calculations of MS^10?₆ clusters (M = Mn, Fe, Co, Ni) have been performed making use of the X_α discrete variational method. The results of the calculations are used for the detailed interpretation of the X-ray emission and photoelectron spectra for Mn, Fe, Co and Ni monosulphides and in a discussion of the physical-chemical properties of the compounds under investigation.     

YBa2(Cu0.95M0.05)3O7-δ的代换效应及其中子衍射研究

X射线衍射实验表明YBa₂(Cu_0.95M_0.05)₃O_7-δ(M=Ti,V,Cr,Mn,Fe,Co,Ni,Cu和Zn)均为单相结构。Fe,Co,Ni和Zn对Cu的替代使超导临界温度T_c显著下降,而同样含量的Ti,V,Cr,Mn对Cu的替代并未对超导性能产生显著影响。并利用中子衍射分析了Ti,Mn,Fe和Co对Cu原子的取代,发现代换原子对Cu的两个晶位各自存在不同的择优占据 关键词：     

Magnetic and transport properties in Sr1−xLaxFe1−xMnxO3

The magnetic and transport properties in the perovskite Sr_1−xLa_xFe_1−xMn_xO₃ have been explored. As x rises, the systemic ferromagnetism increases gradually and cluster-spin-glass state occurs in the low-temperature region. For 0.3?x?0.7, the ferromagnetic phase separation from the paramagnetic phase was observed from the results of electron-spin-resonance measurement. Although all samples show a semiconducting behavior, their transport properties are dominated by two different mechanisms, namely, the electronic transport of x?0.5 samples is realized by thermal activation but the variable-range hopping is applied in x?0.7 ones. The different transport mechanism can be understood from the Mn/Fe ions interaction.     

X-ray photoemission and magnetometric studies of valence changes in Ce(Cu1−xNix)4Ga

The compounds Ce(Cu_1−xNi_x)₄Ga crystallize in the hexagonal CaCu₅-type structure for the whole doping range 0≤x≤1. The border compounds CeCu₄Ga and CeNi₄Ga represent a heavy fermion and fluctuating valence systems, respectively. We report on the studies of the valence evolution in Ce(Cu_1−xNi_x)₄Ga employing the X-ray photoemission spectroscopy (XPS) and magnetic susceptibility measurements. The photoemission of the Ce 3d peaks shows a gradual decrease of the occupation of the f states with Ni content. Simultaneously, the hybridization strength and the low temperature magnetic susceptibility are reduced. Within the valence band spectrum a transition from the dominance of the Cu 3d to the dominance of the Ni 3d states is well visible with the traces of the Ce 4f¹ states for up to x=0.5.     

NMR of 69Ga, 71Ga,and 51V in V3−xFex Ga alloys

We have studied at room temperature the intensities and the Knight shifts of the nuclear magnetic resonances of ⁶⁹Ga, ⁷¹Ga, and ⁵¹V in V_3?xFe_xGa for Fe concentrations ranging from x = 0.04 to x = 0.6. The results interpreted in terms of a redistribution of the conduction electrons and a paramagnetism due to the Fe impurities.     

EPR spectra of Fe centers in layered TlGaSe2 single crystal

A single-crystal TlGaSe₂ doped by paramagnetic Fe ions has been studied at room temperature by electron paramagnetic resonance (EPR) technique. The fine structure of EPR spectra of paramagnetic Fe³⁺ ions was observed. The spectra were interpreted to correspond to the transitions among spin multiplet (S=5/2, L=0) of Fe³⁺ ion, which are splitted by the local ligand crystal field (CF) of orthorhombic symmetry. Four equivalent Fe³⁺ centers have been observed in the EPR spectra and the local symmetry of crystal field at the Fe³⁺ site and CF parameters were determined. Experimental results indicate that the Fe ions substitute Ga at the center of GaSe₄ tetrahedrons, and the rhombic distortion of the CF is caused by the Tl ions located in the trigonal cavities between the tetrahedral complexes.     

First order magnetic phase transition in tetragonal NpCu2Si2

Magnetization and Np²³⁷ Mössbauer studies of the tetragonal compounds NpM₂Si₂ (M = Cr, Mn, Fe, Co, Ni, Cu) were performed. NpMn₂Si₂ is ferromagnetic. All other compounds order antiferromagnetically. Only in NpCu₂Si₂ the Mössbauer studies reveal a first order magnetic phase transition at T_N = 34 K. It is interpreted in terms of Blume's model, originally developed for cubic UO₂.     

Magnetic and electrical transport properties in the self-doped manganite La0.9Mn0.9M0.1O3 (M=Mn,Zn and Ti)

The magnetic and electrical transport properties of La_0.9Mn_0.9M_0.1O₃ (M=Mn, Zn and Ti) were investigated. The temperature and magnetic field dependence of electrical resistivity (ρ) and dc magnetization were studied. All the compounds are found in rhombohedral structure. The excess oxygen in all three compounds was detected through iodometric titration. A modification in resistivity is observed when M=Mn is replaced by M=Zn and Ti. The high temperature resistivity above T_C follow variable range hopping model for both Zn and Ti compounds. For Zn doping, the observation of large field-cool effect and decrease in resistivity at room temperature and is assumed to be due to the implant of Mn⁴⁺ in Mn³⁺ matrix, which favor Mn³⁺/Mn⁴⁺ double exchange. The ferromagnetic behavior below T_C for the compound with M=Ti is correlated to the excess oxygen in it, which implants Mn⁴⁺ and thus incorporates ferromagnetic interactions. The substitutions lead to a reduction of T_c and magnetization.     

Decay studies of neutron-rich products from 76Ge induced multinucleon transfer reactions including the new isotopes 62Mn, 63Fe and 71, 72, 73Cu

By irradiating a ^natW target with 9 MeV/u ⁷⁶Ge ions, neutron-rich isotopes in the chromiumgermanium region were produced. On-line mass-separated samples were investigated. The new isotopes ⁶²Mn, ⁷¹Cu, ⁷²Cu and ⁷³Cu were identified and their half-lives measured to be 0.88(15), 19.5(16), 6.6(1) and 3.9(3) s, respectively. The half-life of ⁶³Fe, a nucleus which has previously been detected using particle-identification techniques, was measured to be 4.9(5) s. Decay schemes were derived in most cases. Additional spectroscopic information was obtained on the decays of ⁷³Zn and ⁷⁴Zn. We give evidence that the earlier reported γ-ray activity attributed to ⁶⁷Ni belongs to the decay of the ⁷⁰Cu isomers. At A = 67 we observed a new β-ray activity of 21(1) s half-life which is here assigned to the decay of ⁶⁷Ni.     

Tb0.3Dy0.7(Fe0.9T0.1)1.95合金的结构、自旋重取向和穆斯堡尔谱

系统研究了室温下Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95(过渡金属元素T=Mn，Fe，Co，B，Al，Ga)合金中ⅢA族金属和过渡金属元素T替代Fe对结构、自旋重取向和穆斯堡尔谱的影响.结果发现，不同金属T替代Fe，Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95，合金具有相同的MgCu₂型立方Laves相结构；Al，Ga替代使Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95合金的易磁化方向在{110}面逐渐偏离了立方晶体的主对称轴，即自旋重取向，B，Mn，Co替代未使易磁化轴发生明显转动；Al，Ga元素替代使超精细场H_hf略有下降，B，Mn替代对超精细场H_hf的影响不大，而Co元素替代使超精细场H_hf有较大增加；所有元素替代使同质异能移IS有所增加；B，Al，Ga和Mn替代使四极劈裂Q_s增加，而Co替代使四极劈裂Q_s下降. 关键词： 立方Laves相 自旋重取向 穆斯堡尔谱     

The effect of transition element doping on the electronic and magnetic properties of La1.4Sr1.6Mn2O7

The effect of transition element (TE=Cr, Fe, Co, Ni, Cu, Zn) doping on the electronic transport and magnetic properties in the bilayer manganite La_1.4Sr_1.6Mn₂O₇ is studied for the same dopant concentration fixed at 2%. Doping does not cause change in structure but different behavior in magnetic and transport properties. Except for Cr, all the other dopings significantly shift the magnetic transition temperature (T_C) to a lower temperature. Associated with such a decrease, the insulator-metal transition temperature (T_IM) decreases and the peak resistivity (ρ_p) at T_IM increases. Cr doping enhances T_C and T_IM as well as decreases ρ_p. Fe doping apparently has a stronger effect than Co and Ni doping. It is also indicated that Cu doping causes an anomalously large increase in ρ_p. These behaviors are compared with those observed in other bilayer manganites such as La_1.2Sr_1.8Mn₂O₇ as well as in La_0.7Ca_0.3Mn_1−xTE_xO₃.     

Direct observation of new proton rich nuclei in the region 23≦Z≦29 using A 55A.MeV58Ni beam

Using magnetic separation and identification through time of flight andΔExE measurements, the nuclei⁵⁶Cu,⁵²Co (T _z =?1);⁵⁵Cu,⁵¹Co,⁴⁷Mn,⁴³V(T _z =?3/2)⁵²Ni,⁵⁰Co,⁴⁸Fe,⁴⁶Mn,⁴⁴Cr (T _z =?2); and⁵¹Ni (T _z =?5/2) are observed for the first time from interactions of 55A.MeV⁵⁸Ni projectiles with a Ni target. The predicted proton drip-line has probably been reached for the odd elements.     

Transferred hyperfine fields at 119Sn in Fe1−xMxSn [M≡Mn, Co and Ni]

The transferred hyperfine fields at ¹¹⁹Sn, using Mössbauer spectroscopy are reported for the hexagonal B-35 compounds with a general formula Fe_1?xM_xSn, where MMn, Co and Ni. In these compounds, Sn atoms occupy two crystallographically inequivalent sites. For FeSn the observed spectrum consists of a quadrupole doublet and a magnetic pattern corresponding to 2(d) and 2(a) sites respectively. The data have been analysed to resolve the controversy regarding hyperfine parameters. On replacing Fe by Mn atoms, additional lines appear in the higher velocity region of the Mössbauer spectrum and the intensity of the nuclear Zeeman pattern increases at the expense of quadrupole doublet. The resulting Mössbauer spectra have been analysed by taking only the nearest neighbour interactions into account. This analysis shows that on replacing each Fe atom by a Mn atom, the hyperfine field at 1(a) Sn site increases by about 40 kOe and a field of about 35 kOe is produced at the 2(d) Sn sites. Further, from the nuclear Zeeman pattern for 2(d) sites, the sign of quadropole splitting for these sites could also be determined and was found to be positive. However, the substitution of Co and Ni in place of Fe atoms results in a broad unresolved pattern suggesting that the hyperfine field at the 1(a) sites decreases and a finite field develops at the 2(d) site. The origin of transferred hyperfine fields at the two inequivalent Sn sites is discussed, the magnetic transition temperatures of these compounds have been estimated and the magnetic moments of M-atoms have been inferred.     

非晶态Fe86M4Zr10合金的磁性和电性

本文研究了非晶态Fe₈₆M₄Zr₁₀(M=V,Cr,Mn,Fe,CO,Ni,Cu,B,Si)合金的基本磁性和低温电性,讨论了不同元素M的掺杂对FeZr合金居里温度和磁矩的影响,并用相干交换散射模型解释了样品在居里温度附近出现的电阻率极小。 关键词：     

Mössbauer and magnetization studies of the NpM2Ge2(M=Cr,Fe, Co,Ni, Cu) intermetallic compounds

Magnetization and ²³⁷Np Mössbauer studies were performed on tetragonal NpM₂Ge₂ intermetallic compounds. All the compounds order antiferromagnetically. The Néel points and the magnetic hyperfine interactions of the NpM₂Ge₂ compounds are 62(3), 28(3), 36(5), 27(3), 34(3) K and 2860(40), 1800(40), 3040(40), 2600(40), 2330(90) Mc/sec for M=Cr, Fe, Co, Ni and Cu respectively.     

Nd0.5Pb0.5-xSrx (Mn, Fe)O3的局域结构畸变和磁输运性质的研究

通过X光衍射，穆斯堡尔谱和输运性质的测量研究了掺杂Fe的Nd0.5Pb0.5-xSrxMnO3样品的结构和磁输运性质。x光衍射和穆斯堡尔谱都表明了样品随Sr的增多结构畸变减小。Sr的掺杂同时也降低了室温时的电阻率并使磁电阻增大。由于在样品中Mn3+ 与 Mn4+的比率是一样的，也就意味着具有相同的双交换作用。所以Sr对样品性质的改变可以认为是由于晶格畸变所产生的。由于Jahn-Teller 效应而产生的Mn(Fe)O6八面体的局域结构畸变可以局域电子。由我们的实验可以看到在居里温度Tc以上，除了双交换作用之外，Jahn-Teller 效应对于输运性质也起了重要作用。     

Oxide ion conductivity of double doped lanthanum gallate perovskite type oxide

Doping transition metal cation is known to enhance the electronic conduction of solid electrolytes, however, the ionic conduction can also be improved by those dopants. In this investigation, the oxide ion conductivity of LaGaO₃ based oxide doped with transition metal cations such as Fe, Co, Ni, Mn, and Cu for the Ga site was studied. It was found that doping Co or Fe is effective for enhancing the oxide ion conductivity. The improved oxide ion conductivity may be induced by the improved mobility of oxide ion. Among examined transition metal cations, cobalt is the most adequate cation as a dopant for the Ga site of LSGM. Considering the conductivity and the transport number, the optimized composition is found to be La_0.8Sr_0.2Ga_0.8Mg_0.115Co_0.085O₃. In this work, application of Co²⁺ doped LSGM as the electrolyte of internally reformed fuel cells was also investigated. Improvement in oxide ion conductivity is effective for enhancing the power generation characteristics. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Magnetic,electrical transport and electron spin resonance studies of Fe-doped manganite LaMn0.7Fe0.3O3+δ

We have investigated the magnetic, electrical transport and electron spin resonance (ESR) properties of polycrystalline Fe-doped manganite LaMn_0.7Fe_0.3O_3+δ prepared by sol–gel method. A typical cluster-glass feature is presented by DC magnetization and AC susceptibility measurements and a sharp but shallow memory effect was observed. Symmetrical Lorentzian lines of the Mn/Fe spectra were detected above 120 K, where the sample is a paramagnetic (PM) insulator. When the temperature decreases from 120 K, magnetic clusters contributed from ferromagnetic (FM) interaction between Mn³⁺ and Mn³⁺/Fe³⁺ ions develop and coexist with PM phase. At lower temperature, these FM clusters compete with antiferromagnetic (AFM) ones between Fe³⁺ ions, which are associated with a distinct field-cooled (FC) effect in characteristic of cluster-glass state.     

Transport behavior and mechanism of conduction of simultaneously substituted Y and Fe in La0.7Ba0.3MnO3 perovskite

The electrical properties and the mechanism of conduction of the simultaneously substituted La_0.7−xY_xBa_0.3Mn_1−xFe_xO₃ perovskite (0≤x≤0.30) have been studied. The insertion of Y³⁺ and Fe³⁺ ions in the parent compound La_0.7Ba_0.3MnO₃ leads to an increase of the resistivity. The undoped sample (x=0) shows a metallic behavior, which can be fitted by the relation ρ(T)=ρ₀+ρ₂T²+ρ_4.5T^4.5, indicating the importance of electron-magnon scattering effects in this material. All the other samples (x≥0.10) are semiconductors throughout the studied temperature range (80-290 K). Several models have been used to fit their temperature-dependent resistivity: thermal activation, adiabatic nearest-neighbor hopping of small polarons (Holstein theory) and variable range hopping (VRH) models. The fits show that the electronic transport in semiconducting La_0.7−xY_xBa_0.3Mn_1−xFe_xO₃ is well described and dominated by the VRH mechanism, for which the hopping distance (a) grows with increasing Fe³⁺ doping, thus increasing the average hopping energy W.     

Effect of the simultaneous substitution of two transition metals on the structural, magnetic and electrical properties of La0.6Sr0.4Mn1−2xCrxFexO3

The structural, magnetic and electrical properties of Cr and Fe simultaneously substituted in the perovskite La_0.6Sr_0.4Mn_1−2xCr_xFe_xO₃ have been studied. The presence of Cr and Fe had no significant effect on the structural properties. Curie temperature and saturation magnetization decrease with increase in Cr and Fe contents. For x=0.20 and 0.25, a steep drop of zero field-cooled (ZFC) magnetization at low temperature signifies the formation of cluster- or spin-glass state. A weak hysteresis at low fields seems to be an indication of phase separation. All the resulting magnetization curves can be explained by a superposition of both ferromagnetic and antiferromagnetic components. All the samples are semiconducting throughout the temperature range studied. Resistivity can be described by the adiabatic small polaron hopping and the variable range hopping model. It was found that the transport mechanism is dominated by the VRH model with an increase of Mott localization energy, which explains the increase of resistivity.