PrRu_{2}Si_{2} shows ferromagnetism below 14 K with the ordered moment of 2.7μ_{B}. It exhibits an enormous magnetic anisotropy at 4.2 K with the anisotropy field of about 400 T. We have attrributed the magnetism of PrRu_{2}Si_{2} to the Pr^{3+} ions. Thus we performed calculations of the fine electronic structure of the Pr^{3+} ion in the tetragonal symmetry, relevant to PrRu_{2}Si_{2}, taking into account crystal-field and inter-site exchange interactions. Our calculations reproduce well the zero-temperature moment, the single-crystalline magnetization curves, and giant anisotropy field as 400 T. The magnetocrystalline-anisotropy energy K_{1} of 59 J/cm^{3} is the largest known anisotropy - the anisotropy energy of the Nd_{2}Fe_{14}B supermagnet amounts to 12.5 J/cm^{3} only. Unfortunately, this giant anisotropy is confined to low temperatures only which prohibits its technical applications in the permanent-magnet industry.
We report on magnetic measurements and electronic structure investigations of CeNiSn and CeRhSb. Both belong to the group of Kondo insulators. The magnetic susceptibility shows the nonmagnetic ground state for these compounds and their alloys. The 3d X-ray photoemission spectroscopy spectra show evidence for the mixed valence state of Ce in CeRhSb alloys, as also seen for CeNiSn, whereas the spectra for the La substituted (Ce,La)NiSn compounds show only evidence for a pure Ce^{3+} ground state. We suggest the presence of Kondo-hole states in (Ce,La)RhSb. The location of the pseudogap in CeRhSb varies with the number of free electron, the valence of Ce, and the f-d hybridization. We discuss the similar crystallographic properties and the closed electronic structures of ZrNiSn-type semi-Heusler alloys and CeNiSn-type Kondo insulators.
The crystal of Ce_5Ni_2Si_3 was prepared by the Czochralski method. The X-ray photoemission spectroscopy was measured for the valence band and the core levels. Based on the Ce(3d) doublet and its satellites a small value of the hybridization parameter of the f-states with the conduction electrons Δ=4 meV and the f-occupancy n_f close to 1 were found. X-ray photoemission spectroscopy shows that the region between 0 and 3 eV is predominated by the Ni(3d) and Ce(4f) peaks. Some features of the multiplet structure of the Ce(4f) states are also visible close to the Fermi level.
Experimental data show that aluminium doped RCo_5 systems crystallize in CaCu_5-type structure for most of the rare-earth elements (R). Al impurities randomly occupy one of the two possible positions (2c and 3g) and there is a critical concentration of Al, x_c=2.0, for RCo_{5-x}Al_x when the Co sublattice becomes nonmagnetic. The ab initio self-consistent calculations show strong dependence of magnetic properties of GdCo_{5-x}Al_x on concentration of Al and position of the impurities in the unit cell, furthermore to fulfil experimental observation of existence of critical concentration, x_c=2.0, the Al impurities should prefer 3g positions otherwise the magnetic moments on Co atoms do not vanish.
Surfaces of three selected materials were investigated by means of low-energy ion-scattering technique: (1) the magnetite (Fe_3O_4) exhibiting the so-called Verwey transition (T_V(bulk)=125 K) accompanied by a small cubic-monoclinic crystal distortion, (2) the intermetallic compound NdMn_2 undergoing an antiferromagnetic-paramagnetic phase transition (T_N=104 K) accompanied by a large crystal distortion with a volume change of 1%, and (3) the typical insulator BaTiO_3 with two structural transitions below 300 K. The primary energy of the (Ne^+, Ar^+) ion beam was in the range of 4-8 keV, and the low-energy ion-scattering spectra were collected in the temperature range of 85-300 K. A large influence from the Verwey transition on the neutralization and re-ionization of scattered ions from magnetite surface was observed, while no visible change at the magnetic phase transition in NdMn_2 was revealed in the low-energy ion-scattering spectra. A strong dependence of the characteristics of the low-energy ion-scattering spectra on the irradiated time was observed for BaTiO_3 indicating that this surface was heavily charged by ion bombardments.
The electronic structure and magnetic properties of La_{1-x}Ce_{x}Pb_3 and La_{1-x}Pr_{x}Pb_3 are studied using the spin-polarized relativistic Korringa-Kohn-Rostoker coherent potential approximation method within the local spin density approximation. The calculated density of states at the Fermi level increases with the increase of the concentration. The dependence of spin and orbital magnetic moments of La_{1-x}Ce_{x}Pb_3 and La_{1-x}Pr_{x}Pb_3 (0 < x < 1) on the concentration is also reported. The densities of states at the Fermi energy are dominated by Ce(Pr) 4f_{5/2} and 4f_{7/2} states.
The magnetic properties of CeCoMn, Ce₃Co₃Mn₄ and Ce₃Co₆Mn alloys have been investigated by magnetization and susceptibility measurements in the temperature range (5-300) K and magnetic field up to 12 T. X-ray powder diffraction measurements showed that all three alloys are isostructural and crystallize in the cubic MgCu₂ structure type. Both Ce and Co atoms are non-magnetic in all alloys like in the isostructural compound CeCo₂. Magnetic behavior of the investigated alloys is mostly due to the Mn moments and depends essentially on the Mn-Mn distances. The interaction between the Mn moments is antiferromagnetic in CeCoMn and Ce₃Co₃Mn₄ but a paramagnetic behavior for Ce₃Co₆Mn was evidenced in the studied temperature range.
The effect of twin boundaries on the normal and fluctuating conductivity of ReBaCuO (Re = Y, Ho) single crystals was investigated. The results indicate that the Lawrence-Doniach theoretical model describes adequately the temperature dependence of the excess conductivity. The twin boundaries are efficient scattering centers for normal and fluctuating carriers. The derived values of the coherence length perpendicular to the ab-planeξ_c(0) are in good agreement with those obtained from magnetic measurements for stoichiometric YBaCuO crystals.
The heat capacity in the applied magnetic field up to 9 T, susceptibility and magnetization of polycrystalline CeCu_{4}Ga are presented. Magnetic ordering was not observed down to 2 K. For temperature T < 200 K a Curie-Weiss behavior is observable giving an effective magnetic moment μ_{eff} =2.53 μ_{B}/f.u. The experimental value of μ_{eff} is close to the calculated one for a free Ce^{3+} ion (μ_{eff} = 2.54 μ_{B}/f.u.), thus indicating the presence of well localized magnetic moments carried by the stable Ce^{3+} ions. At low temperatures the electronic heat capacity coefficient value depends strongly on the temperature range used for the extrapolation and applied magnetic field. We observe a typical heavy fermion behavior with γ value of about 380 mJ mol^{-1} K^{-2} obtained from extrapolation to T = 0 K of the temperature range above 7 K. However, extrapolation of the lowest temperatures range yields the γ value of 3.3 J mol^{-1} K^{-2}.
In this work we investigate the conductivity in the basis plane of YBa_2Cu_3O_{7-x} and Y_{1-z}Pr_zBa_2Cu_3O_{7-x} single crystals with a system of one-direction twin boundaries. The Pr dopants behave as efficient scattering centers of normal and fluctuating carriers. For this a slight doping with praseodymium (till z≈0.05) results in a significant narrowing of the temperature interval in which the pseudo-gap regime is realized in the ab-plane of YBaCuO single crystals.
The study of the heat capacity of the intermetallic compound NdNi_{4}Si including the effect of the magnetic field is reported. This compound crystallizes in the hexagonal CaCu_5-type structure, space group P6/mmm. NdNi_{4}Si is ferromagnetic with T_C = 8 K and the saturation magnetic moment of 1.5 μ_{B}/f.u. at 4.2 K (in H = 9 T). The heat capacity was analyzed considering the electronic contribution, the Schottky anomaly, and the lattice contributions in the frames of the Debye model. The scheme of the energy levels created by the crystal electric field split is determined from the Schottky contribution to the specific heat. NdNi_{4}Si was characterized by the electronic heat capacity coefficient γ = 85 mJ/(mol K^2) and the Debye temperature Θp_D = 325 K.
Based on the electronic structure of the ferromagnetic Gd_{2}In and (Gd_{0.5} Y_{0.5})_{2}In compounds the high-temperature magnetic part of the electrical resistivity of (Gd_{1-x}Y_{x})_{2}In as a function of Y concentration was calculated and analyzed. The main interaction which causes the finite magnetic part of the conductivity was assumed in a form of stochastically distributed in space s-f interaction. The calculated resistivity of (Gd_{1-x}Y_{x})_{2}In alloys qualitatively reproduces the experimental data.
Thin Sm layers adsorbed on Mo(110) and (211) surfaces were studied with scanning tunneling microscope. It was found that obtained images of these adsorption systems significantly depend on the polarity of the scanning tunneling microscope bias voltage. This dependence is more pronounced for the Sm on Mo(110) than on Mo(211). For Sm/Mo(110), at low Sm coverages the change of bias polarity results in significant difference in the measured height of the adsorbed Sm layer, while the heights of substrate terraces remain the same for both signs of the applied bias voltage. In the coverage range 0.65<θ<1, scanning tunneling microscope images, obtained with negative bias, show the gaps in Sm layers, which are invisible for positive bias.
In the present study the rapidly quenched Pr_9Fe_{50 + x}Co_{13}Zr_1Nb_4B_{23 - x} (x = 0, 2, 5, 8) alloy samples produced in a form of 100 mm^2 plate of various thicknesses were investigated. The X-ray diffraction revealed changes in the phase constitution of as-cast samples depending on the alloy composition and plate thickness. The presence of hard magnetic Pr_2(Fe,Co)_{14}B phase was observed in 0.5 mm thick plates of the x = 8 alloy, while fully glassy structure was shown in 0.5 mm thick plates of the x = 0 alloy. It was shown in the present paper that magnetic properties of annealed samples originated from different microstructure of as-cast samples.
High quality single crystals of some representatives of half-Heusler family were grown from Bi-flux. For single crystals characterization, X-ray diffraction and scanning electron microscopy techniques were used. The low-temperature physical properties of the synthesized crystals were determined by means of magnetization, magnetic susceptibility, electrical resistivity and heat capacity measurements. For each compound but LuPtBi, the electrical resistivity varies in a semimetallic manner at high temperatures, and exhibits a metallic character at low temperatures. LuPtBi is metallic in the whole temperature range studied. The bismuthides HoPdBi, LuPdBi, LuPtBi and YPtBi were found superconducting below the critical temperature T_{c} = 0.7, 1.8, 0.9, and 0.96 K, respectively. For the compounds GdPdBi, DyPdBi and HoPdBi, an antiferromagnetic ordering was found to set in below T_{N} = 12.8, 3.7, and 1.9 K, respectively. HoPdBi is thus an intriguing material in which both cooperative phenomena coexist.
Magnetization reversal processes in the magnets derived from the Fe_{60}Co_{13}Zr_1Ti_3Pr_9B_{14} alloy were investigated. It was shown that the processing technique affects the magnetization reversal processes. For the nanocrystalline ribbon samples pinning of the domain walls arises at low external magnetic fields while nucleation of reversed domains occurs at higher fields. However, the nucleation fields are lower than the pinning fields for the nanocrystalline rod and tube samples produced by suction-casting technique.
The electronic structure of the ternary YNi_4B compound, crystallizing in the hexagonal CeCo_4B structure (P6/ mmm space group), was studied by X-ray photoelectron spectroscopy and ab initio calculations. Core levels and the valence band were investigated. The X-ray photoelectron spectroscopy valence band is compared with that obtained from ab initio calculations. The valence band spectrum at the Fermi level exhibits the domination of the Ni(3d) states, which are hybridized with 4d states of Y and 2p states of B. The theoretical electronic specific heat coefficientγ derived from N(E_F) is about 11.33 mJ/(mol K^2) for experimental lattice parameters. The calculated bulk modulus is B_0=1.61632 Mbar.
The electronic structure of the ternary CeTIn (T = Ni, Cu, Pd, Au) compounds was investigated by means of X-ray photoelectron spectroscopy. Our interest was aimed mainly to the valence bands and the Ce3d core levels of investigated compounds. Analysis of the valence bands indicates that they are mainly determined by the Tnd band, whereas a share of the R4f states can be estimated to be about a few percent only. The analysis of the differential valence bands spectra between CeTIn and LaTIn analogues suggests that the Ce4f^1 ground states shift deeper below the Fermi level with an increase in the 4f level occupation factor. The analysis of the Ce3d spectra made on the basis of the Gunnarsson-Schönhammer model indicates the hybridization parameter equal to 148 meV for CeNiIn, 45 meV for CeCuIn, 177 meV for CePdIn, and 123 meV for CeAuIn.
In the present work, the influence of annealing conditions on magnetic properties and phase constitution of the rapidly solidified Fe₆₅Pr₉B₁₈W₈ alloy ribbons, were investigate. Samples were prepared by arc-melting of high purity constituent elements under the Ar atmosphere. Ribbons were obtained by melt-spinning technique under low pressure of Ar. The ribbons in as-cast state had amorphous structure and soft magnetic properties. Heat treatment, carried out at various temperatures (from 923 K to 1023 K) for 5 min, resulted in an evolution of the phase constitution that caused changes in magnetic properties of the alloy. The crystallization behavior was studied using differential scanning calorimetry and X-ray diffractometry. The room temperature magnetic properties were determined from hysteresis loops measured by VSM magnetometer in the external magnetic field up to 2 T.
The electronic structure of Ce_{1-x}La_{x}PtIn is studied by means of ab initio full-potential local orbital basis (coherent potential approximation) (FPLO-CPA) and spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR-CPA) methods within the densities functional methodologies. In both methods, we have observed decrease of the density of states at the Fermi level versus of La concentration. The theoretical photoemission spectra of LaPtIn and CePtIn are compared with the experimental data and the agreement is good. We have also reported the optical properties of LaPtIn and CePtIn compounds obtained in GGA and GGA+U approximation.
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