72 research outputs found
Effects of spin polarization on resonant photoemission from d-f states in TbNi2Mnx compounds
Resonant photoemission in narrow-band materials is described by the sum of first-and secondorder transitions, their quantum-mechanical interference leads to an increase in the spectrum from the valence bands and the appearance of an asymmetric dependence on the photon energy. These effects are studied theoretically and experimentally using the example of three-component intermetallic compounds TbNi2Mnx. The competition between the elastic and inelastic photoemission channels leads to a different dependence of photoemission spectra from nickel and manganese on photon energy. The elastic channel is realized on atoms with large magnetic moments, the inelastic Auger decay occurs on atoms with small moments. © 2018 The Authors, published by EDP Sciences.The research was carried out within the state assignment of FASO of Russia (theme uQ" ant" No. 01201463332), supported in part by RFBR (No. 18-02-00060) and UD RAS (No.15 -8 2-10). The authors express their gratitude to A. Preobrazhenskii and N. Vinogradov (synchrotron MAX-Lab, Lund, Sweden) for their assistance in carrying out experiments
Magnetic properties of the non-stoichiometric TbCo2Nix alloys
The magnetic and magnetothermal properties of the non-stoichiometric TbCo2Nix (0 ≤ x ≤0.2) alloys were studied. It was found that the concentration dependence of the Curie temperature and magnetic moment of the 3d-sublattice have a maximum at x = 0.025. The obtained experimental magnetic properties of the TbCo2Nix alloys were discussed under assumption that the Co magnetic moment in the compounds changes with increasing x. The magnetic entropy change was determined using the temperature dependences of the magnetization and Maxwell's thermodynamic relation. The obtained results for TbCo2Nix were compared with those for the ErCo2Mnx alloys. © 2018 The Authors, published by EDP Sciences.The research was carried out within the state assignment of )$62 of 5Xssia (thePe ³0aJnet´ 1o ȺȺȺȺ-Ⱥ - 118020290129 -5) and supported by project of UB RAS (No. 18-10-2-5)
Magnetic and magnetocaloric properties of (MnCo)1-xGe compounds
The crystal structure, magnetic properties, and heat capacity of the (MnCo)1-xGe compounds with x ≤ 0.05 have been studied. It was found that, as the deviation from the MnCoGe stoichiometric composition increases, the temperature of structural transition from the low-temperature phase with the orthorhombic TiNiSi-type structure to the high-temperature phase with the hexagonal Ni2In-type phase decreases rapidly, whereas the magnetic ordering temperature varies slightly. The temperature of structural transition for the composition with x = 0.02 approximately coincides with the Curie temperature of the hexagonal phase, and the transition is accompanied by a significant entropy change, namely, ΔS = 34 J/(kg K). The application of high magnetic field in the transition-temperature range causes an increase in the relative volume of the orthorhombic phase. An analysis of magnetocaloric properties of these compounds, which was performed with the formal application of the Maxwell's relationship near the temperature of first-order structural phase transition, is shown to give overestimated values of the entropy change. © Pleiades Publishing, Ltd., 2013
High field x-ray diffraction study on a magnetic-field-induced valence transition in YbInCu4
We report the first high-field x-ray diffraction experiment using synchrotron
x-rays and pulsed magnetic fields exceeding 30 T. Lattice deformation due to a
magnetic-field-induced valence transition in YbInCu4 is studied. It has been
found that the Bragg reflection profile at 32 K changes significantly at around
27 T due to the structural transition. In the vicinity of the transition field
the low-field and the high-field phases are observed simultaneously as the two
distinct Bragg reflection peaks: This is a direct evidence of the fact that the
field-induced valence state transition is the first order phase transition. The
field-dependence of the low-field-phase Bragg peak intensity is found to be
scaled with the magnetization.Comment: 5 pages, 6 figures, submitted to J. Phys. Soc. Jp
Mechanism and Kinetics of Interaction of FLiNaK–CeF3 Melt with Water Vapors and Oxygen in the Air Atmosphere
The mechanism and kinetic parameters of the interaction of the FLiNaK–CeF3 melt with water vapors and oxygen in the air atmosphere were determined using Raman and IR spectroscopy, XRD analysis, and thermodynamic modeling of processes. The presence of the 4CeF3(solution) + 6H2O (gas) + O2(gas) = 4CeO2(solid) + 12HF(gas) reaction, which disturbs the fluoride melt homogeneity, was verified in situ by Raman spectroscopy adopted for high-temperature, chemically aggressive fluoride systems. Based on the obtained spectral data, the type of the kinetic equation, order, and rate constant of the chemical reaction were determined. The concentration of cerium dioxide was found to increase linearly in time and a zero reaction order with respect to CeO2 was detected. The change in the concentration of CeO2 over time at T = 510 °C is described by the equation C = 0.085t; the reaction rate constant is 0.085 mol. %∙min−1. The obtained kinetic parameters may be used to model emergencies related with the depressurization of the coolant circuit or the working area of the molten salt reactor. © 2023 by the authors
Magnetic properties of the non-stoichiometric TbCo2Mn x and TbCo2Nix alloys
The crystal structure, magnetic and magnetothermal properties of non-stoichiometric TbCo2Mnx and TbCo2Nix alloys were studied. It was shown that single-phase compounds with the MgCu2-type structure exist up to a certain content of x (x < 0.4 for compounds with Mn and x ≤ 0.1 for compounds with Ni). The concentration changes of the lattice parameter, Curie temperature, magnetic moment of the 3d sublattice in TbCo2Mn x and TbCo2Nix alloys were compared. The magnetocaloric effect in alloys were estimated using data of magnetic and heat capacity measurements. © Published under licence by IOP Publishing Ltd.Russian Foundation for Basic Research, RFBR: 18-02-00294The research was carried out within the state assignment of Minobrnauki of Russia (theme “Magnet” No. АААА-А18-118020290129-5), supported in part by RFBR (project No. 18-02-00294)
Electrical resistivity, magnetism and electronic structure of the intermetallic 3d/4f Laves phase compounds ErNi2Mnx
The non-stoichiometric intermetallic compounds RENi2Mnx (RE = rare earth) with
the cubic MgCu2-type structure display a large variety of magnetic properties which
is due to a complex interplay between the degrees of freedom of the 3d and
4f electrons and their interactions. We performed a comprehensive study of the
electrical resistivity, magnetic properties and the electronic structure of ErNi2Mnx
(x =0, 0.25, 0.5, 0.75, 1, 1.25) compounds by employing a suitable set of complementary
experimental approaches. We find an increase in electrical resistance compared
to ErNi2 upon Mn doping, the residual resistivity ratio decreases with increasing
manganese content. The Curie temperature exhibits a sharp increase to around 50 K
for Mn concentrations x 0.5, whereas the saturation magnetization decreases
with growing Mn content x 0.5. Valence band X-ray photoelectron spectroscopy
reveals an increasing intensity of Mn 3d states near Fermi energy in dependence
of Mn concentration and Curie temperature. Resonant photoelectron spectroscopy
of ErNi2Mn0.75 reveals that the photoemission decay channels dominate the valence
band spectra across the Er N5 and Mn L3 X-ray absorption maxima, whereas the
L3VV Auger dictates the resonant valence band spectra close to and at the Ni L3
X-ray absorption edge
Strong Longitudinal Magnetic Fluctuations near Critical End Point in UCoAl: A ^59Co-NMR Study
We report ^59Co-NMR measurements in UCoAl where a metamagnetism occurs due to
enhancement of ferromagnetism by magnetic field. The metamagnetic transition
from a paramagnetic (PM) state to a ferromagnetic state is a first order
transition at low temperatures, but it changes to a crossover at high
temperatures on crossing the critical end pint (CEP) at T_CEP ~ 12 K. The
contrasting behavior between the relaxation rates 1/T_1 and 1/T_2 suggests that
the longitudinal magnetic fluctuation of U moment is strongly enhanced
especially near the CEP. A wide diffusion of the fluctuation from the CEP can
be confirmed even in the PM state where the magnetic transition does not occur.Comment: 5pages, 6 figures, to be published in J. Phys. Soc. Jp
Charge screening and magnetic anisotropy in metallic rare-earth systems
The calculation of magnetic anisotropy constants is performed beyond the
point charge model for a continuous charge density distribution of screening
conduction electrons. An important role of the non-uniform electron density, in
particular, of the Friedel oscillations, in the formation of crystal field is
demonstrated. Such effects can modify strongly the effective ion (impurity)
charge and even change its sign. This enables one to justify the anion model,
which is often used at discussing experimental data on hydrogen-containing
systems. Possible applications to the pure rare-earth metals and RCo5 compounds
are discussed. The deformation of magnetic structure near the interstitial
positive muon owing to the strong local anisotropy, and the corresponding
contribution to the dipole field at the muon are considered.Comment: 10 pages, RevTeX, 3 figure
- …