High pressure study of a Zr-based bulk metallic glass and its composite

Energy dispersive X-ray diffraction was used to study the structural evolution of a bulk metallic glass (BMG) alloy and its composite with W particles under hydrostatic pressure. The diffraction data, especially the pair distribution function (PDF) of the BMG allowed the direct measurement of its elastic strain. The results suggest that PDF patterns of BMGs can be used to deducetheir strain evolution in composites as well as in monolithic form. Although the PDF method of strain measurement in amorphous alloys offers lower resolution compared to the analysis of Bragg reflections from crystalline materials, the PDF techique yields valuable information about the deformation of BMGs

Vibrational modes in nanocrystalline iron under high pressure

The phonon density of states (DOS) of nanocrystalline 57Fe was measured using nuclear resonant inelastic x-ray scattering (NRIXS) at pressures up to 28 GPa in a diamond anvil cell. The nanocrystalline material exhibited an enhancement in its DOS at low energies by a factor of 2.2. This enhancement persisted throughout the entire pressure range, although it was reduced to about 1.7 after decompression. The low-energy regions of the spectra were fitted to the function AEn, giving values of n close to 2 for both the bulk control sample and the nanocrystalline material, indicative of nearly three-dimensional vibrational dynamics. At higher energies, the van Hove singularities observed in both samples were coincident in energy and remained so at all pressures, indicating that the forces conjugate to the normal coordinates of the nanocrystalline materials are similar to the interatomic potentials of bulk crystals

High pressure study of a Zr-based bulk metallic glass and its composite

Energy dispersive X-ray diffraction was used to study the structural evolution of a bulk metallic glass (BMG) alloy and its composite with W particles under hydrostatic pressure. The diffraction data, especially the pair distribution function (PDF) of the BMG allowed the direct measurement of its elastic strain. The results suggest that PDF patterns of BMGs can be used to deducetheir strain evolution in composites as well as in monolithic form. Although the PDF method of strain measurement in amorphous alloys offers lower resolution compared to the analysis of Bragg reflections from crystalline materials, the PDF techique yields valuable information about the deformation of BMGs

Itinerant-localized dichotomy in magnetic anisotropic properties of U-based ferromagnets

The electronic structure, spin and orbital magnetic moments, and the magnetic anisotropy energy in selected U-based compounds are investigated making use of the correlated band theory. First, we demonstrate that the LSDA+U approach with exact atomic limit implemented as a combination of the relativistic density functional theory with the Anderson impurity model provides a good quantitative description for UGa2. Further, the method is applied to UFe12 and UFe10Si2 ferromagnets. The calculated positive uniaxial magnetic anisotropy together with negative enthalpy of formation for UFe10Si2 make it as a candidate for the magnetically hard materials. Our studies suggest a viable route for further development of the rare-earth-lean permanent magnets by replacing a part of U atoms by some rare-earth like Sm in UFe10Si2.Web of Science131art. no. 264

Structure and properties of Tb2Pd2Mg hydride

Hydrogen exposure of Tb2Pd2Mg crystallizing in the tetragonal Mo2FeB2 structure results in the absorption 8 \ub1 1 H/f.u. The absorption is not reversible and leads to a structure transition yielding a new structure type (Pearson symbol oI40, space group Fmmm). Tb2Pd2Mg is an antiferromagnet with TN  48 60 K showing 2 metamagnetic transitions. Upon hydrogenation the susceptibility cusp related to AF ordering disappears and the susceptibility increases monotonously with decreasing temperature. Magnetic remanence, which starts to develop below 20\u201325 K, can be attributed to a randomness in H sites occupancy

Structural investigation of Np2Co17 and analogue compounds under pressure

The structural behavior of Np2Co17 is investigated by means of high-pressure diamond-anvil compression measurements and is compared with that of the isostructural compounds Lu2Co17 and Lu2Ni17. The Th2Ni17-type hexagonal crystal structure is preserved with no measurable discontinuous volume collapses up to the highest achieved pressure, p = 43 GPa. For Np2Co17, fits to the Birch-Murnaghan and Vinet equations of state give values of the isothermal bulk modulus and its pressure derivative of B0 = 286 GPa and B 0= 3, revealing that this Np compound is a highly incompressible solid with stiffness comparable to that of superhard covalently bonded materials. For the Lu2T17 (T = Co, Ni) compounds, the measured bulk modulus changes from B0 = 137 GPa for T = Co to B0 = 257 GPa for T = Ni. The isothermal equation of state for the studied compounds are in excellent agreement with the results of ab initio fully relativistic, full-potential local spin-density functional calculations. Theoretical estimates of the bulk modulus are given also for Np2Ni17, for which B0 is predicted to assume values intermediate between those measured for Lu2Ni17 and Np2Co17.JRC.E.6-Actinide researc

Superconductivity and Mössbauer Effect in Actinides

Superconductivity, discovered more than 100 years ago, still remains challenging for condensed matter physics, 50 years after the BCS theory on superconductivity. Actinide materials and their 5f electrons play an important role in this field, with a large number of uranium heavy fermion magnetic superconductors reported in the last three decades and, more recently, the discovery of transuranium unconventional superconductors : PuCoGa5, PuRhGa5, PuCoIn5 and NpPd5Al2. The paramagnetic heavy fermion NpPd5Al2 (Tc = 4.9K and = 200 mJ mole-1 K-2) is the only neptunium-based superconductor known so far. A recent novel model has predicted a possible temperature-dependence with an extremum of the charge density in NpPd5Al2. In order to check this prediction and using the 237Np Mössbauer resonance, we have measured the temperature dependence of the isomer shift of NpPd5Al2 with the best experimental accuracy possible and found a small extremum.JRC.E.6-Actinide researc

Low-temperature magnetic properties of NpNi5

We present the result of an extended experimental characterization of the hexagonal intermetallic Haucke compound NpNi5. By combining macroscopic and shell-specific techniques, we determine the 5f-shell occupation number nf close to 4 for the Np ions, together with orbital and spin components of the ordered moment in the ferromagnetic phase below Tc=16 K (μS = −1.88 μB and μL = 3.91 μB). The apparent coexistence of ordered and disordered phases observed in the Mössbauer spectra is explained in terms of slow relaxation between the components of a quasitriplet ground state. The ratio between the expectation value of the magnetic dipole operator and the spin magnetic moment (3Tz/Sz = +1.43) is positive and large, suggesting a localized character of the 5f electrons. The angular part of the spin-orbit coupling ( · s = −5.55) is close to the value of -6.25 calculated for trivalent Np ions in intermediate coupling approximation. The results are discussed against the prediction of first-principle electronic structure calculations based on the spin-polarized local spin density approximation plus Hubbard interaction, and of a mean field model taking into account crystal field and exchange interactions.JRC.E.6-Actinide researc