Rare Earth Metals Gd Research Articles

Temperature-Induced Reversal of Magnetic Interlayer Exchange Coupling

For epitaxial trilayers of the magnetic rare-earth metals Gd and Tb, exchange coupled through a nonmagnetic Y spacer layer, element-specific hysteresis loops were recorded by the x-ray magneto-optical Kerr effect at the rare-earth M5 thresholds. This allowed us to quantitatively determine the strength of interlayer exchange coupling (IEC). In addition to the expected oscillatory behavior as a function of spacer-layer thickness dY, a temperature-induced sign reversal of IEC was observed for constant dY, arising from magnetization-dependent electron reflectivities at the magnetic interfaces.

Rhodium supported on thermally enhanced zeolite as catalysts for fuel reformation of jet fuels

Autothermal reformation of military jet fuel (1096 ppmw sulfur) was investigated with rhodium supported on thermally stabilized Y zeolite catalysts. The zeolite catalysts were thermally stabilized by ion exchanging with nitrate solutions of rare-earth metals (La, Ce, Sm, Gd, Dy and Er). Surface area analyses indicated that the exchanged zeolite could maintain its porous structure as high as 950 °C instead of 800 °C for a commercial NaY zeolite. The structure of the exchanged zeolite was characterized by X-ray diffraction (XRD). Rh-SmNaY zeolite reforming catalysts were prepared by incipient wetness and organometallic synthesis. The JP8 reforming experiments were performed in a short contact time adiabatic reactor with a monolithic catalyst with the addition of air and steam at a temperature below 920 °C. The effects of steam and fuel-to-air ratio (C/O ratio) were studied. Hydrogen and carbon monoxide were produced as the main products. Durability tests were performed with Rh/SmNaY-zeolite catalysts. This work shows that zeolite based catalysts can convert transportation fuels such as high sulfur jet fuel (over 1000 ppmw S) to syngas for solid oxide fuel cell applications.

A comparison study of the entropy changes in materials with and without short-rangemagnetic order

The effects of short-range magnetic order (SRMO) on magnetic entropy changes have been studied for thecompounds Sm0.55Sr0.45MnO3, Eu0.55Sr0.45MnO3 and the rare-earth metal Gd. Ferromagnetic clusters composed of∼8 Mn ions are found to be formed in the paramagnetic phase of the manganites based on theanalysis of susceptibility. As a result, the entropy change for a field variation of 0–5 T is∼6 J kg−1 K−1 forSm0.55Sr0.45MnO3 and∼7 J kg−1 K−1 forEu0.55Sr0.45MnO3, wellbelow the values expected without considering the effect of SRMO. (The maximum entropy change willbe ∼56 J kg−1 K−1 for both compounds.) Assuming the presence of sizable magnetic clusters, the field-inducedentropy change, not only its peak value but also its temperature dependence, can bewell reproduced by the mean field theory. The average cluster size is found to bem≈8, in agreement with the result obtained from a Curie–Weiss analysis ofthe susceptibility. The presence of SRMO reduces the entropy change by∼80%. In contrast, the mean field theory gives a good description of the entropy change in Gd,for which no significant SRMO is observed. The present work reveals the important role ofSRMO in modifying the magnetocaloric properties of the magnetic materials.

Quasiparticle self-consistentGWmethod applied to localized4felectron systems

Rare-earth pnictides possess unique electronic and magnetic properties that make them interesting for both fundamental and practical reasons. We apply the quasiparticle self-consistent $GW$ $(\mathrm{QS}GW)$ method to the rare-earth metals Gd and Er and to the rare-earth monopnictides GdN, EuN, YbN, GdAs, and ErAs. $\mathrm{QS}GW$ is unique in that it automatically takes into account both $spd$ and $f$ electrons in a single, unified framework without any materials-dependent parameters or special treatment of the $f$ electrons. It enables us to examine approximations behind the standard local density $\text{approximation}+U$ and self-interaction corrected approaches. $\mathrm{QS}GW$ reproduces the experimental occupied $4f$ levels well, though the unoccupied levels are a little overestimated. Properties of the Fermi surface responsible for electronic properties---governed by the $spd$ electrons---are in good agreement with available experimental data. GdN is predicted to be very near a critical point of a metal-insulator transition.

Development of permanent magnetic refrigerator at room temperature

A reciprocating magnetic refrigerator was developed based on the active magnetic regeneration technology. Rare earth metal Gd and intermetallic compound LaFe 11.2Co o.7Si 1.1 were used as the magnetic operating materials in the machine. The particles of the magnetic operating materials, with diameter of 0.5 – 2 mm and total mass of 950 g, were mounted in the cooling bed. A magnetic field was assembled using NdFeB rare earth permanent magnets. It had the magnetic field space of ϕ 34 × 200 and the magnetic induction of 1.5 T. The water at pH = 10 is used as a heat transfer fluid. When the ambient temperature is 296 K, a temperature span of 18 K was achieved after operation of 45 min at a frequency of 0.178 Hz. The temperature span and the output power increase significantly with the increasing velocity of heat transfer.

Optical properties of heavy rare earth metals (Gd–Lu)

We report calculations of the optical properties of heavy rare earth metals (Gd–Lu) using the full potential linear augmented plane wave method with inclusion of spin orbit coupling. Calculations are performed using the LSDA and LSDA+ U approximations. Our calculations show that LSDA+ U gives a better representation of the band structure and density of states than LSDA. The optical conductivity with LSDA+ U is in better agreement with experiment than that from LSDA at low energies. At high energies, LSDA and LSDA+ U yield similar optical conductivities. We find a general shift in the structures of the optical conductivity towards higher energies on going from Gd to Lu. Optical conductivity is dominated by transitions between p and d states. Our results are in good agreement with experiment for all the rare earth metals considered.

Technique for Preparing Ultrafine Nanocrystalline Bulk Material of Pure Rare‐Earth Metals

The unique configuration of unpaired 4f and 5f electrons and the rich structures of their energy levels enable rare-earth metals to possess many particular physical and chemical properties, such as high electrical conductivity, large magnetic moment, and very high complexation reactivity. Based on these properties, the rare-earth metals and compounds have been applied extensively in permanent magnets, autocatalysts, superconductors, etc. Demand for high-purity rareearth oxides and rare-earth metals is expected to increase particularly for use in corrosion resistance, heat storage and dispersal, and also in environmentally friendly applications such as in pigments for paint and plastics, in cement manufacture to reduce the temperature of calcination and help save energy, and in refrigeration components arising from the search for chlorofluorocarbon (CFC) replacements. For the nanoscale rare-earth metals, because of the significantly increased total surface area or the grain boundary area, some new features show in the crystal structures, interface, thermodynamics, and phase transitions. Consequently, remarkably improved optical, electronic, magnetic, and catalysis properties can be expected. However, because of the extremely high chemical reactivity and hence the considerably rigorous equipment requirements to preserve a high purity of the product, the preparation and characterization of nanostructured pure rare-earth metals are still big challenges in nanoscience and nanotechnology. Thus, many important features of nanoscale rare-earth metals, such as the physical, chemical, thermal, and mechanical characteristics have rarely been reported so far. The research corresponding to these characteristics is of great importance, however, both for the development of nanoscience and nanotechnology and for extending the applications of the rareearth metals. In this consideration, we demonstrate in the present work how to prepare nanostructured bulk materials of some typical members of the rare-earth metals, laying the foundation for characterizing the physical and chemical properties of nanoscale rare-earth metals. During the past two decades, a number of techniques have been developed to synthesize nanocrystalline bulk materials, such as inert gas condensation and consolidation, electrodeposition, severe plastic deformation, crystallization of amorphous solids, surface mechanical attrition, and powder metallurgy. However, it is hard to produce nanocrystalline materials with controllable grain sizes in a wide range below 100 nm. Furthermore, in powder metallurgy for the consolidation of nanoparticles, the grain size in the synthesized bulk is generally larger than the initial particle size. Particularly, in conventional powder metallurgy processes, a rapid coarsening of nanoparticles occurs very often, leading to the formation of grains in the submicrometer or even micrometer range. Using a new “oxygen-free” (oxygen concentration < 0.5 ppm) in-situ synthesis, where inert gas condensation was combined with spark plasma sintering (SPS) in an entirely closed system, we prepared nanocrystalline bulk material of pure rare-earth metals (Nd, Sm, Gd, and Tb) with ultrafine (< 20 nm) nanograins. Taking into account the special mechanisms of SPS consolidation, which were proposed in the literature and were recently developed in our previous work, we designed a preparation scheme with sequentially arranged processes of: amorphization of nanoparticles, nucleation and growth of the short-range ordered “clusters” inside the nanoparticle, and the complete nanocrystallization, as shown in the diagram in Figure 1. By this approach we have realized the preparation of bulk nanocrystalline materials of pure rare-earth metals. The most significant advantage of this technique is that the grain size of the resultant nanocrystalline bulk is distinctly smaller than the initial nanoparticle size, which is the first demonstration to the best of our knowledge that the traditionally accepted relationship between the size of the initial powder particles and the grain size of the sintered bulk can be changed by our modified powder metallurgy technology. In virtue of this technique, nanocrystalline bulk materials with controllable grain C O M M U N IC A TI O N S

Studies on the Synthesis and Potentiometric Properties of Three Novel Tripodal Ligands and their Complexes

Three novel tripodal ligands, N,N′,N′′-tri-(3′-phenylpropionic acid-2′-yl-)-1,3,5-triaminomethylbenzene (Ll), N,N′,N′′-tri-(4′-methylvaleric acid-2′-y1-)-1,3,5-triaminomethylbenzene (L2) and N,N′,N′′-tri-(3′methylvaleric acid-2′-yl-)-1,3,5-triaminomethylbenzene (L3), have been synthesized and fully characterized. The stabilizing ability of complexes of the three ligands with transition metal ions Cu(II), Ni(II), Zn(II) and Co(II) and rare earth metal ions La(III), Nd(III), Sm(III), Eu(III) and Gd(III) has been investigated by the pontentiometric method in water and in aqueous KNO3 (0.1 mol dm−3) at 25.0±0.1 °C, respectively. The results show that there is a great deal of difference between two series of complexes’ stabilities. An explanation of the difference has been given.

Eutectic Modification of Al-Si Alloys with Rare Earth Metals

The effects of different concentrations of individual additions of rare earth metals (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) on eutectic modification in Al-10mass%Si has been studied by thermal analysis and optical microscopy. According to the twin-plane re-entrant edge (TPRE) and impurity induced twinning mechanism, rare earth metals with atomic radii of about 1.65 times larger than that of silicon, are possible candidates for eutectic modification. All of the rare earth elements caused a depression of the eutectic growth temperature, but only Eu modified the eutectic silicon to a fibrous morphology. At best, the remaining elements resulted in only a small degree of refinement of the plate-like silicon. The samples were also quenched during the eutectic arrest to examine the eutectic solidification modes. Many of the rare-earth additions significantly altered the eutectic solidification mode from that of the unmodified alloy. It is concluded that the impurity induced twinning model of modification, based on atomic radius alone, is inadequate and other mechanisms are essential for the modification process. Furthermore, modification and the eutectic nucleation and growth modes are controlled independently of each other.

Point-defect properties in HCP rare earth metals with analytic modified embedded atom potentials

The analytic embedded atom method (EAM) type many-body potentials of hcp rare earth metals (Dy, Er, Gd, Ho, Nd, Pr, and Tb) have been constructed. The hcp lattice is shown to be energetically most stable when compared with the fcc and bcc structure, and the hcp lattice with ideal c/a. The mechanical stability of the corresponding hcp lattice with respect to large change of density and c/a ratio is examined. The phonon spectra, stacking fault and surface energy are calculated. The activation energy for vacancy diffusion in these metals has been calculated and the most possible diffusion paths are predicted. Finally, the self-interstitial atom (SIA) formation energy and volume have been evaluated for eight possible sites. This calculation suggests that the crowdion and basal split are the most stable configurations. The SIA formation energy increases linearly with the increase of the melting temperature.

Strain-induced interaction of hydrogen atoms in hcp rare earth metals

The energies of strain-induced (elastic) H–H and D–D interaction are calculated for the hcp rare earth metals Sc, Y, Gd, Tb, Dy, Ho, Er, and Lu taking into account the discrete atomic structure of the host lattice. The elastic constants, lattice spacing of the host lattice, and concentration expansion coefficients of the solid solution lattice due to dissolved atoms are the input numerical parameters used. The interaction is oscillating and is of the long-range nature. In all solid solutions, a significant elastic attraction exists in the first two coordination shells. A comparative analysis of H–H and D–D interaction energies in hcp metals with those in bcc and fcc solid solutions revealed the determining effect of the crystal lattice type on both interaction energy value and its dependence on interatomic distances. The difference between the interaction energies for different rare earth metals is also significant. In general, the strain-induced H–H and D–D interactions in hcp rare earth metals are weaker than in bcc solid solutions and are of the same order as in fcc solid solutions.

Formation of surface intercalation compounds at Gd(Dy)/graphite interfaces under thermal annealing

Angle-resolved valence-band and C 1s core-level photoemission was used to study growth of surface intercalation-like phases upon deposition of trivalent rare-earth metals (Dy and Gd) onto a (0 0 0 1) surface of single-crystalline graphite and highly oriented pyrolytic graphite and subsequent annealing at increasing temperatures, T anneal.. It was found that the synthesis of the surface intercalation compounds ( T anneal.∼1100°C) undergoes a stage of carbide formation ( T anneal.∼900°C). It was concluded that after the high temperature annealing the Gd(Dy)/graphite interfaces reveal layered structure and can be described as thin layers (up to one monolayer) of surface intercalation-like compounds grown on the top of (1 1 1) surfaces of Gd- and Dy-dicarbides.

Investigation of properties of rare earth complexes with dibromo-p-methyl-methylsulfonazo by spectral correction technique

The reactions were sensitive between seven rare earth (RE) metals Nd(III), La(III), Ce(III), Pr(III), Sm(III), Eu(III) and Gd(III) and dibromo-p-methylmethylsulfonazo (DBMMSA) in acidic solution. The spectral correction method has been applied in the determination of properties of RE complexes instead of ordinary spectrophotometry. Composition ratios, real molar absorptivities (ε) and stepwise stability constants (K) of each of the RE complexes were determined easily because the method eliminated the absorption influence of excess of ligand on complex. Results showed that the cumulativeK values of the complexes were between 3.91 × 1014 and 2.34 × 1028 and the real (not apparent) absorptivity between 8.85 × 104 and 2.12 × 105 l mol-1cm-1 at 640 nm.

Structural, Electronic, and Magnetic Properties of Ternary Rare-Earth Metal Borocarbides R5B2C5 (R=Y, Ce–Tm) Containing BC2 “Molecules”

The borocarbides R5B2C5 (R=Y, Ce–Tm) were prepared by arc melting from the pure rare-earth metals, boron and carbon. The structural arrangement of these compounds, which crystallize in the tetragonal space group P4/ncc, consists of a three-dimensional framework of rare-earth atoms resulting from the stacking of slightly corrugated two-dimensional squares, which lead to the formation of octahedral holes and distorted bicapped square antiprismatic cavities filled with isolated carbon atoms and C–B–C chains, respectively. In contrast to the heavy rare-earth metal (Gd–Tm)-containing compounds which melt congruently, those with the early rare-earth elements (Ce–Sm) are formed peritectically. The electronic structure and chemical bonding of Sm5B2C5 and Gd5B2C5 are analyzed using extended Hückel tight-binding and density-functional theory calculations. Results reveal a rather strong covalency between the metallic matrix and the BC2 groups and the isolated carbon atoms, respectively, similar to what is generally computed in related rare-earth metal borocarbides. Magnetic susceptibility measurements indicate that all samples, which were investigated, undergo ferromagnetic transitions in the temperature region below T=130 K. The heavy rare-earth metal (Tb–Tm) borocarbides exhibit a magnetic behavior typical of narrow-domain-wall ferromagnets. Both the Curie temperatures, TC, as well as the paramagnetic Curie temperatures, ΘP, scale approximately with the de Gennes factor. Hence the indirect exchange interaction via conduction electrons (RKKY-interacting) is the dominating force of the R–R coupling mechanism.

High pressure μSR studies: rare earths and related materials

After a short introduction to μSR with respect to the study of magnetic properties, followed by a brief outline of the principle of the high pressure-low temperature μSR spectrometer installed at the Paul Scherrer Institute, we discuss some measurements on rare earth materials employing this instrument. They are concerned with: (1) The pressure dependence of the spin turning process in ferromagnetic Gd. (2) The volume dependence of the internal magnetic field in the heavy rare earth metals Gd, Dy, and Ho in their ordered magnetic states. (3) The response of the (first order) magnetic transition in the frustrated antiferromagnets of type RMn2 (R = Y,Gd) to pressure. (4) The variation of magnetic parameters with pressure in La2CuO4 (powder sample), the antiferromagnetic parent compound of the high TC superconductors of type La2−x(Sr, Ba)xCuO4. In conclusion a short outlook on further developments is given.

Mesoporous Magnetic Materials Based on Rare Earth Oxides

A novel family of mesoporous oxides of rare earth metals (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were synthesized with specific surface areas of 253–348 m2 g−1 and pore diameters of 2.5–3.0 nm (see Scheme). The mesoporous solids and their surfactant mesophase precursors are paramagnetic and exhibit a magnetic anomaly due to the mesostructured atomic arrangement.

Mesoporous Magnetic Materials Based on Rare Earth Oxides.

A novel family of mesoporous oxides of rare earth metals (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were synthesized with specific surface areas of 253-348 m(2) g(-1) and pore diameters of 2.5-3.0 nm (see Scheme). The mesoporous solids and their surfactant mesophase precursors are paramagnetic and exhibit a magnetic anomaly due to the mesostructured atomic arrangement.

Magnetic properties of endohedral fullerene complexes

The type as well as the electronic state of endohedral fullerene complexes have been determined by the simultaneous application of mass spectrometry, ESR spectroscopy and magnetic measurements. Endohedral fullerenes containing the rare earth metals Eu, Gd, Tm and Yb give mass spectra corresponding to singly and double filled cages. But the expected ESR spectra were not found, Magnetizati-on-vs.-temperature/field measurements showed the Gd to be trivalent, whereas the Eu is divalent in the endohedral fullerenes.

Core-level spectroscopy study of rare-earth metal/W(110) interface formation

The electronic structure of rare-earth metal/W(110) interfaces during the initial stages of deposition has been investigated using core-level shift spectroscopy. Three rare-earth metals (Gd, Y and Yb) have been grown on a W(110) substrate. Shifts in the W core level peaks of > 300 meV have been confirmed for the clean W(110) surface. On completion of each interface a bulk feature and only one shifted peak is observed which supports evidence that no alloying occurs. At submonolayer coverages an additional feature is seen at higher kinetic energies which is attributed to emission from W atoms under various adsorbate structures.

Magnetocaloric effect in the vicinity of magnetic phase transition

The paper discusses the adiabatic magnetization processes (magnetocaloric effect) in the region of magnetic phase transitions, based on known data about magnetic phase diagrams and the magnetocaloric effect of the rare-earth metals Gd and Dy. A correlation between an arrangement of lines of the magnetic phase transitions on (H, T) diagrams and a corresponding value of magnetocaloric effect were assumed.