Magnetic properties of the uranium sesquichalcogenides

Magnetic measurements on the orthorhombic uranium sesquichalcogenides and orthorhombic U₃Te₄ were performed in the temperature range 4.2–1000 K and in magnetic fields up to 140 kOe. The temperature dependence of the reciprocal susceptibility was found to be curvilinear for all the investigated compounds. At low temperatures U₂Te₃ and U₃Te appeared to be antiferromagnetic below 106 K. U₂Se₃ and U₂S₃ seem to have a more considerable ferromagnetic contribution below 60 and 80 K, respectively. The magnetic properties are discussed in terms of crystal structure and related properties of the investigated compounds.     

Magnetic properties of uranium ferrocyanides and ferricyanides

The uranium ferricyanide and ferrocyanide have been synthesized. It has been shown that the prepared compounds are ferromagnetically ordered in the low temperature region with the critical temperature T _c = 4.3K and T _c = 4.41 K, respectively.     

Magnetic ordering in uranium monophosphide

The magnetic ordering in uranium monophosphide (UP) has been studied by neutron diffraction from a single crystal in a magnetic field. UP orders at T_N ? 122 ± 0.1 K with the type-I antiferromagnetic structure (+-+-), the ordering taking place in a first-order transition. At T₀ = 22.5 K the ordered magnetic moment jumps from 1.7 μ_B to 1.9 μ_B. With a magnetic field H = 25 kOe applied along the [11&#x0304;10] direction, it is found that UP has the collinear single-$\text{K}$ type-I structure above T₀ and undergoes a first-order transition to the planar double-$\text{K}$ type-I structure, accompanied by a “moment jump” due to the change in the moment direction from <001> to <110>.     

Magnetic properties of thorium and uranium borides and U1−xThxB4 solid solutions

The dependence of the magnetic susceptibility on the temperature in the compound UB₄ and system U_1–xTh_xB₄ has been studied in the temperature range 140–1300°K. It has been established that the paramagnetic susceptibility does not obey the Curie-Weiss law. The experimental results are interpreted on the basis of the Stoner model of collectivized electrons which also makes it possible to explain the magnetic properties of other borides of thorium and uranium.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, No. 7, pp. 45–48, July, 1982.     

Lattice vibrational properties of uranium pnictides

Lattice vibrational properties of uranium pnictides have been studied using breathing shell model (BSM) which includes breathing motion of electrons of the U-atoms due tof−d hybridization. The phonon dispersion curves of U-pnicitides calculated from the present model agree reasonably well with the measured data. A comparison has been made between BSM and our results reported earlier obtained from three-body force rigid ion model to reveal the importance of the short-range electron-phonon interactions in these compounds. We also report, for the first time, the two phonon density of states and specific heat for these compounds.     

Magnetic properties of tetragonal uranium compounds I. the U2N2Z-ternaries

In the present work we report the magnetic behaviour of the tetragonal ternaries of the U₂N₂Z-type (Z=Sb, Bi and Te). Magnetic susceptibility measurements performed in a wide temperature range (4.2–1000 K) have shown, that they are ferromagnetically ordered with Curie temperatures 166, 154 and 71 K for U₂N₂Sb, U₂N₂Bi and U₂N₂Te, respectively. For all the investigated compounds the κ^-1_M(T) function in the temperature range above T_C can be expressed as (A/T + B)^-1 - λ.Magnetization measurements were carried out up to magnetic field strengths of 140 kOe in the temperature range from 4.2 to the respective T_C. It follows from these measurements that σ(T)_H and σ(H)_T for U₂N₂Sb and U₂ N₂Bi are typical as for normal ferromagnets. On the other hand, U₂N₂Te exhibits, unexpectedly, two distinct maxima on the σ(T) curves up to fields of 4.5 kOe; one at 45 K and the other one at 71 K. Previous neutron diffraction studies of this compound have shown that the magnetic moments of uranium atoms at 4.2 K are titled by about 20° from the basal plane.The results obtained are interpreted in terms of the crystal-field interaction of the 5f² electrons of the U⁴ ion. In consequence a γ_5t doublet is expected to be the ground-state crystal field level in the U₂N₂Z-type as well as in many other ternary uranium tetragonal compounds. However, in the case U₂N₂Te, the singlet-singlet-doublet “band” as a ground system is postulated.     

Magnetic properties of GdMg

The lattice constants at room temperature and the magnetic properties of several members of the series Gd_χLa_1-χMg were studied in the temperature range 4.2–300 K with applied fields up to 340 kG. Several of the pseudo-binary compounds were found to give rise to antiferromagnetic ordering in low applied fields. In their magnetic isotherms at 4.2 K critical fields occur which are associated with the destruction of the antiferromagnetic ground state. These critical fields were found to increase with La concentration. It is shown that in Gd_χLa_1-χMg the antiferromagnetic interaction between the Gd spins decreases with increasing χ whereas the ferromagnetic interaction increases in the same sense. In GdMg the antiferromagnetic interaction has almost completely vanished, so that superficially this compound looks like a normal ferromagnet.     

Magnetic properties of ferrihydrite

The magnetic properties of a sample of synthetic ferrihydrite have been investigated by use of Mössbauer spectroscopy. The area ratios of the Mössbauer lines are not significantly changed by application of magnetic fields at 5 K, indicating an amorphous magnetic structure. An average magnetic moment per particle of 3.1×10^?21 JT^?1 was estimated from the dependence of the hyperfine splitting of the Mössbauer spectra on external magnetic fields at 80 K.     

Magnetic hyperfine fields on119Sn nuclei in uranium compounds

119Sn Mössbauer spectroscopy studies were performed on 12 uranium intermetallic compounds in order to investigate correlations between the formation of the magnetic moment on the U atom and the magnetic hyperfine field transferred to 119Sn nuclei in magnetically ordered materials. The measured hyperfine fields (H_hf) are related to the values of the ordered U magnetic moments (UB) by U_oH_hf/n=A UU. The parameter A varies between 0.73 (UGa2) and 1.55 (UGe2). It seems to correlate with the extent of the hybridization of the 5f states with the conduction electron states.     

Fission decay properties of ultra neutron-rich uranium isotopes

The fission decay of highly neutron-rich uranium isotopes is investigated which shows interesting new features in the barrier properties and neutron emission characteristics in the fission process. ²³³U and ²³⁵U are the nuclei in the actinide region in the beta stability valley which are thermally fissile and have been mainly used in reactors for power generation. The possibility of occurrence of thermally fissile members in the chain of neutron-rich uranium isotopes is examined here. The neutron number N = 162 or 164 has been predicted to be magic in numerous theoretical studies carried out over the years. The series of uranium isotopes around it with N = 154–172 are identified to be thermally fissile on the basis of the fission barrier and neutron separation energy systematics; a manifestation of the close shell nature of N = 162 (or 164). We consider here the thermal neutron fission of a typical representative ²⁴⁹U nucleus in the highly neutron-rich region. Semiempirical study of fission barrier height and width shows that ²⁵⁰U nucleus is stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. On the basis of the calculation of the probability of fragment mass yields and the microscopic study in relativistic mean field theory, this nucleus is shown to undergo exotic decay mode of thermal neutron fission (multi-fragmentation fission) whereby a number of prompt scission neutrons are expected to be simultaneously released along with the two heavy fission fragments. Such properties will have important implications in stellar evolution involving r-process nucleosynthesis.      

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运用密度泛函理论方法,采用MS中CASTEP模块计算了铀晶体的能量随体积变化的关系,并绘制了E-V曲线。运用准谐振子德拜模型计算了压强从0~100GPa、温度从0~2000K下的晶体铀的相对体积,发现相对体积随着温度和压强的增加而减小。并成功得到了热膨胀系数、热容、以及体弹模量随温度和压强的变化关系。预测了铀的热力学性质。为铀晶体在高温高压下的实验研究提供了理论依据。     

Magnetic properties of amorphous alloys

The magnetic properties of existing amorphous iron based materials, i.e., Fe--metalloid, Fe--early transition metals and Fe--rare earth alloys, are briefly discussed for some representative alloys. The spin orientation of amorphous Fe--metalloid alloys has been determined by the angular dependence of hyperfine interactions. It is shown that in iron--early transition metals ferromagnetic order is not long-ranged, but determined by magnetic clusters. The magnetic hyperfine field distributions of Fe-rich iron--early transition metals consist of a high and a low field tail. The magnetic structure has been investigated for two representative Fe--RE (RE = Er, Ce) amorphous alloys. For the first time, the magnetic coupling phenomenon in amorphous/crystalline multilayers has been discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetic properties of carbon nanosheets

Two-dimensional carbon nanosheets have been fabricated using inductively coupled radio frequency plasma-enhanced chemical vapour deposition. The structural properties of the nanosheets have been characterised using atomic force microscopy, scanning electron microscopy and X-ray diffractometer. The magnetisation of the samples was studied using vibrating sample magnetometer. The magnetisation of the nanosheets was found to be diamagnetic for fast synthesis processes (30 and 60 min). On the other hand, the nanosheets exhibited a weak ferromagnetic response for the slow (120 min) synthesis process. Energy dispersive spectrometry and atomic absorption spectroscopy confirmed that the magnetisation exhibited by the carbon nanosheets was an intrinsic property and that it was not due to contamination from the substrate. Raman spectroscopy studies revealed that the ferromagnetic carbon nanosheets have a higher ratio (1.20) of graphite peak (I _G) to disordered peak (I _D) than normally expected (0.75–0.90). Available data indicated that the magnetisation was due to the presence of structural disorders.     

Magnetic properties of neutron matter

The energy of interacting neutron matter with spin polarization is calculated in Hartree-Fock approximation by the method of unitary transformations for a hard core and a soft core potential. In addition the magnetic spin susceptibility is given and the possibility of a ferromagnetic transition investigated. It is shown that the effect of the nuclear forces for all densities considered depresses the magnetic spin susceptibility relative to that of the corresponding ideal Fermi gas.     

Magnetic properties of tetraphenyldithiapyranylidene iodides

Two tetraphenyldithiapyranylidene (DIPS ø₄) polyiodides have been recently synthesized. The static and dynamic paramagnetism behavior are investigated and analyzed. The role of the iodine chains which is peculiar because of different chemical species and structurally non-equivalent chains is shown to be essential to understand the physics of these one-dimensional electronic systems.     

Magnetic properties of neptunium diarsenide

The magnetic properties of a collection of single crystals of NpAs₂ have been investigated in the temperature range 4.2-300 K and in applied fields up to 100 kOe. For small magnetic fields (3 kOe), NpAs₂ is ferromagnetic up to T_IC=18 K, antiferromagnetic from 28 K to T_N=52 K, then paramagnetic. Both transitions are first order. When the applied field increases T_IC is shifted towards T_N. The antiferromagnetic phase disappears for H#62;30 kOe. The ferromagnetic range is characterized by a very large anisotropy. In the paramagnetic state, NpAs₂ has an effective moment 1.88 μ_B.     

Magnetic properties of ErN films

We report a magnetization study of stoichiometric ErN nanocrystalline films grown on Si and protected by a GaN passivating layer. According to the temperature dependence of the resistivity the films are heavily doped semiconductors. Above 100 K the magnetization data fit well to a Curie-Weiss behavior with a moment expected within the free-ion Er³⁺ multiplet. Below 50 K the Curie-Weiss plot steepens to an effective moment corresponding to that in the crystal-field determined quartet ground state, and develops a clear paramagnetic Curie-Weiss temperature of about 4.5 K. Zero-field- and field-cooled magnetization curves and the AC susceptibility firmly establish a ferromagnetic ground state within that multiplet below a Curie temperature of . Due to the (1 1 1) texture of the film the comparison between the magnetization behavior, when the field is applied parallel and perpendicular to the film plane, gives new information about the magnetic structure. An arrangement of the moments according to the model derived from neutron diffraction for bulk HoN is strongly suggested.     

Magnetic properties of zig-zag ladders

We analyze the phase diagram of a system of spin-1/2 Heisenberg antiferromagnetic chains interacting through a zig-zag coupling, also called zig-zag ladders. Using bosonization techniques we study how a spin-gap or more generally plateaux in magnetization curves arise in different situations. While for coupled XXZchains, one has to deal with a recently discovered chiral perturbation, the coupling term which is present for normal ladders is restored by an external magnetic field, dimerization or the presence of charge carriers. We then proceed with a numerical investigation of the phase diagram of two coupled Heisenberg chains in the presence of a magnetic field. Unusual behaviour is found for ferromagnetic coupled antiferromagnetic chains. Finally, for three (and more) legs one can choose different inequivalent types of coupling between the chains. We find that the three-leg ladder can exhibit a spin-gap and/or non-trivial plateaux in the magnetization curve whose appearance strongly depends on the choice of coupling. Received 11 February 1999 and Received in final form 16 June 1999