Gd Er Research Articles

Nanostructural state and magnetism of RFe 2H X hydrides obtained by hydrogen-induced amorphization

The magnetic properties and the structure of hydrogen-amorphized RFe 2H x compounds (R = Y, GdEr) have been studied. During hydrogen-induced amorphization (HIA) the structure of RFe 2 compounds is likely to be decomposed into the areas enriched in R, exchange-uncoupled with Fe, and those enriched in Fe. At least two exchange coupling constants differing by order of magnitude have to be assumed to describe the temperature dependence of the magnetization. From the magnetization measurements the characteristic size of the structural components is estimated to be of the order of a few nanometers. HIA causes noticeable increase of the Fe-magnetic moment and the FeFe exchange interaction, and a decrease of the R-Fe exchange interaction in comparison with analogous crystalline hydrides. The magnetic state of amorphous hydrides is non-uniform and for R = Tb…Er a canted magnetic structure in the R-sublattice is formed owing to a high local uniaxial anisotropy and a low R-Fe exchange interaction.

Structural and magnetic properties of new RRuGe compounds

Investigations made by powder X-ray diffraction and magnetic measurements on new ternary RRuGe compounds (R=Sm, Gd, Tb, Dy, Ho, Er, Tm) are reported. They crystallise in the well-known orthorhombical TiNiSi-type structure (space group Pnma). The RRuGe compounds with R=Gd–Er are Curie–Weiss paramagnets above 77 K. The obtained results are compared with those obtained on isotypic RTX compounds.

Preparation and crystal structure of quaternary silicide carbides with Dy 2Fe 2Si 2C type structure

The compounds A 2Fe 2Si 2C (A=La, Ce, Sm, Th) and A 2Re 2Si 2C (A=Y, La–Nd, Sm, Gd–Er, Th) have been prepared for the first time. They crystallize with the Dy 2Fe 2Si 2C type structure, which was refined for Th 2Re 2Si 2C from single-crystal X-ray data: C2/ m, a=1117.82(9) pm, b=417.53(4) pm, c=702.93(7) pm, β=128.721(7)°, Z=2, R=0.023 for 648 structure factors and 22 variable parameters. Some rhenium is present on the silicon site of this compound, resulting in the exact composition Th 2Re 2.086(4)Si 1.914(4)C. The interatomic distances of this structure are compared with those of the previously reported isotypic and isoelectronic compounds Dy 2Fe 2Si 2C and Tm 2Fe 2Si 2C. The Re–Re bonds within the two-dimensionally infinite rhenium-silicon-carbon polyanion are stronger than the Fe–Fe bonds of the iron compound, while all other bonds in the rhenium–silicon–carbon polyanion (Re–Si, Re–C, Si–Si) are weaker than the corresponding bonds of the iron compound. Thus, the electron count of the transition metal atoms may be close to 18 in both structures, in spite of the differing formal charges of the polyanion: (Fe 2Si 2C) −6 vs. (Re 2Si 2C) −8.

On the thermodynamics of the rhombohedral-cubic phase transition of thulium(III)oxide fluoride

The rhombohedral(β)→cubic(α) phase transition of stoichiometric TmOF and the phase behaviour of samples of the analytical composition Tm(O,F) y with 1.85≤ y≤2.10 were studied by quantitative differential thermal analysis (DTA) and by X-ray powder diffraction analysis. It was found that the β→α transition occurs at 808±3 K with an increment of the formula volume of 0.5±0.05 Å 3, and that α-TmOF decomposes in a peritectoid reaction at ca. 915 K into a fluorite-related, presumably orthorhombic phase of composition Tm(O,F) 1.93 ± 0.02 and an orthorhombic vernier-type phase of composition Tm 9O 8F 11 with a=5.3765(5) Å, b=49.402(5) Å and c=5.4607(4) Å. Tm(O,F) 1.93 is formed by a eutectoid reaction of C-Tm 2O 3 with α-TmOF at ca. 900 K. An accurate determination of the enthalpy of the β→α transition of TmOF was found to be impossible because of the proximity of the temperatures of transition and decomposition. Therefore the enthalpy of transition was determined indirectly by measuring the temperatures and enthalpies of transition of solid solutions Tm 1- x Ca x O 1- x F 1+ x with 0.017≤ x≤0.062 by differential scanning calorimetry (DSC). It was found that both, T tr and Δ tr H T(tr) 0, depend linearily on the CaF 2 content of the solid solutions, and that the decomposition of the cubic α-modification is suppressed by the incorporation of CaF 2 into the TmOF lattice. The following thermodynamic data relating to the β→α phase transition of stoichiometric TmOF could be derived by extrapolation to the formula TmOF: Δ tr H 808 0=5343±267 J mol −1 and Δ tr S 808 0=6.84±0.34 J mol −1 K −1. By correlating the entropies of the β→α transition with the temperatures of transition of ROF with R=Y, La–Tm it was found that the entropies for R=La–Eu and Tm are clustering around 6.6±0.4 J mol −1 K −1 and those for R=Gd–Er and Y around 8.5±0.5 J mol −1 K −1, independently of the cationic radii, and that TmOF occupies a special position within the ROF series.

Magnetic behaviour of RCuAl compounds

We studied structural and magnetic properties of the RCuAl (R=rare earth) intermetallic compounds by means of X-ray diffraction, susceptibility, magnetization and specific heat measurements. Magnetic ordering at low temperatures was observed in most of these materials. Results provide indications of ferromagnetic coupling in the heavy rare-earth compounds (R=Gd–Er), while PrCuAl and NdCuAl show antiferromagnetic behaviour. Additional magnetic phase transition in the ordered state was found in GdCuAl and DyCuAl. A metamagnetic transition was observed in DyCuAl.

Magnetic and electrical resistivity studies on RMn xGe 2 (R=Gd–Er) compounds

A.c. susceptibility and electrical resistivity studies carried out on RMn x Ge 2 (R=Gd–Er) compounds show that all the compounds are antiferromagnets at low temperature. The Néel temperature is between 3.4 K for R=Er and 27 K for R=Tb. The temperature dependencies of the electrical resistivity are typical of metallic conductivity. The resistivity at low temperatures shows for R=Tb and Ho, an anomaly typical of antiferromagnetic materials. A negative temperature coefficient of the resistivity is observed below 5 K for R=Tb and 20 K for R=Er.

Control of electronic properties by lanthanide size and manganese oxidation state in the MnIII/MnIV Ruddlesden–Popper phases Ln2−xSr1+xMn2O7

The magnetic behaviour of then=2 Ruddlesden–Popper phases Sr 2 LnMn 2 O 7 is very sensitive to the Ln 3+ lanthanide cation. In samples with larger, more basic lanthanide cations (Ln=Nd, Pr) antiferromagnetic phases with ordering temperatures in the region of 130 K co-exist with phases showing a magnetic response suggestive of superparamagnetism or the development of small ferromagnetic clusters at high temperature. The magnetic transition temperature drops to 20 K in samples containing smaller, acidic cations (Ln=Gd–Er, Y). In the latter group of compounds, the transition is from a Curie–Weiss paramagnet to a spin-glass; there is no evidence for long-range magnetic order. This change in behaviour can be explained by considering the variation in the relative strength of superexchange and double exchange interactions as a function of the lanthanide cation. The influence of manganese oxidation state on magnetic response is investigated in the Sr 2-x Ln 1+x Mn 2 O 7 composition range (0.0≤x≤0.7) for Ln=Nd, Tb.

Gd2OsC2, a soft ferromagnet with a surprisingly high Curie temperature and other rare-earth osmium and rhenium carbides with Pr2ReC2 type structure

The six new carbides Ln2OsC2 (Ln=Y, Gd–Er) have been prepared by arc-melting cold-pressed pellets of the elemental components with subsequent annealing. They crystallize in the orthorhombic Pr2ReC2 structure (Pnma, Z=4), which was refined from powder diffractometer data of Tb2OsC2 . Chemical bonding in these carbides is discussed. The magnetic susceptibilities of the compounds Ln2OsC2 (Ln=Y, Gd and Tb) have been investigated with a SQUID magnetometer between 2 and 400 K with magnetic flux densities up to 5.5 T. The magnetic susceptibility of Y2OsC2 is low and almost temperature independent, suggesting Pauli paramagnetism. Gd2OsC2 and Tb2OsC2 are ferromagnetic with the relatively high Curie temperatures of 320±5 and 210±5 K, respectively. The gadolinium compound has the rather low coercivity of 23.8±0.4 A cm–1 at room temperature and 31.8±0.8 A cm–1 at 5 K. The magnetic properties of the corresponding rhenium carbides Ln2ReC2 (Ln=Ce, Pr, Nd, Gd, Tm) were also determined, thus completing the magnetic characterization of the rhenium series. The cerium atoms in Ce2ReC2 show mixed-valence behaviour. Antiferromagnetic order was observed for the moments of the rare-earth atoms in Pr2ReC2 , TN=32±2 K; Nd2ReC2 , TN=42±2 K; Gd2ReC2 , TN=100±5 K and Tm2ReC2 , TN=5±3 K.

MHSe: The First Hydride Selenides of the Lanthanides (M = LaNd; GdEr, Lu)

AbstractThe oxidation of most of the lanthanide dihydrides MH2 (M = LaNd; GdEr, Lu) with equimolar amounts of selenium results in the formation of the first lanthanide hydride selenides MHSe. The presence of alkali chlorides (e.g., NaCl or CsCl) as fluxes secures complete and fast reactions (7 d) at 700–850°C in sealed, arc‐welded tantalum capsules (protected by evacuated silica vessels) as well as single‐crystalline products (pale bluish‐gray hexagonal columns or platelets).Two different structures were determined from X‐ray single crystal data for the examples of 2HCeHSe (hexagonal, P63/mmc (no. 194), Z = 2, a = 406.36(4), c = 794.81(9) pm, R1 = 0.0365, wR2 = 0.0766) and 1HHoHSe (hexagonal, P6m2 (no. 187), Z = 1, a = 381.56(3), c = 387.28(5) pm, R1 = 0.0140, wR2 = 0.0337). According to X‐ray powder data, the hydride selenides MHSe with M = LaNd proved to be isostructural with 2H‐CeHSe, those with M = GdEr and Lu crystallize isotypically with 1HHoHSe just like YHSe.Both structures contain hydrogen in half of the trigonal planar interstices within closest‐packed mono‐layers of the metals. These layers [(M3+)(H−)3/3]2+ (a,β or b,α) are alternatively sheethed with closest‐packed mono‐layers of Se2− (C) along [001], and only the stacking sequence decides whether a “stuffed” WC‐ (C(a,β)C  1 H‐MHSe) or a “stuffed” anti‐NiAs‐type arrangement (C(a,β)C(b,α)C  2HMHSe) emerges.

Investigation of the magnetic properties of the Gd 1− xEr x alloy system in the x < 0.62 composition range

The magnetic properties of the GdEr system (with erbium concentrations ranging from 0 to 62 at%) were investigated at temperatures between 4.2 and 350 K under external magnetic fields up to 1 T. The results show that, similar to other rare-earth systems, simple ferromagnetism prevails for concentrations with a de Gennes factor G higher than about 11.5 (≈ 30 at % Er) while complex magnetic structures are present for higher Er concentrations ( G ≤ 11.5. The magnetic transition temperature decreases with increasing Er content, showing good agreement with phenomenological expectations. In the paramagnetic region, the Curie constant of the alloy corresponds to the linear combination of the constituent elements' contribution, thus proving that both Gd and Er maintain their individual magnetic moments. From magnetization data below the transition, the change in magnetic entropy for a 1 T field was calculated and this showed distinct differences between ferromagnetic-paramagnetic transitions and antiferromagnetic transitions. The Landau theory of second-order phase transitions can be well applied for evaluating the thermodynamic transition temperature and the specific heat anomaly in the ferromagnetic alloys but it fails for the more complex structures if the applied field is not far higher than the critical field. The magnetic entropy change displays well defined peaks at the transition temperature for both ferromagnetic and antiferromagnetic alloys. There is an indication that the spin-reorientation transition occurring in alloys with higher Er concentrations is also coupled with significant magnetic entropy changes.

Magnetic properties of the carbides RCoC (R = Y, GdEr, Lu) with YCoC-type structure

The magnetic properties of the carbides RCoC ( R = Y, Gd-Er, Lu) were determined with a SQUID magnetometer between 2 and 300 K at magnetic flux densities of ± 5.5 T. The cobalt atoms of these carbides do not carry magnetic moments as is indicated by the Pauli paramagnetism of the yttrium and the lutetium compound. The others show Curie-Weiss behaviour and the magnetic moments correspond to those of the free R 3+ ions. The reciprocal susceptibility curves of GdCoC and TbCoC suggest ferromagnetism with Curie temperatures of T c = 16(3)K and 22(2) K, respectively. While the terbium compound shows a narrow hysteresis loop at 5 K, no remanence and no coercitivity was found for the gadolinium compound at this temperature. DyCoC, HoCoC and ErCoC are metamagnetic with Néel temperatures between 8 and 4 K. The new isotypic carbide YbCoC was prepared from a lithium flux. It has the tetragonal lattice constants a = 362.6 (1)pm, c = 662.5 (2)pm.

Magnetic and transport properties of the R 3Ni system (R = Y, Gd, Tb, Dy, Ho, Er)

The electrical resistivity and magnetic susceptibility have been measured for Y 3Ni, Gd 3Ni, Tb 3Ni, Dy 3Ni, Ho 3Ni and Er 3Ni single crystals in a wide temperature range. A T 3-dependence and a strong negative curvature of the electrical resistivity were observed for lower temperatures and a saturation effect for higher ones. Y 3Ni exhibits also a very pronounced temperature dependence of the magnetic susceptibility. After subtracting the temperature independent term, Y 3Ni obeys a Curie-Weiss law with μ eff=1μ B per formula unit for the temperature range 10–50 K and with μ eff=0.68μ B for the range 50–420 K. It may indicate the existence of a magnetic moment for the Y-Ni system in spite of such a low Ni concentration. A complex magnetic behaviour and enhancement of the effective magnetic moment in relation to the theoretical value, calculated assuming only R 3+-ion contribution, for Gd 3Ni, Tb 3Ni, Dy 3Ni, Ho 3Ni and Er 3Ni, was observed.

Rare earth separation using a chemical vapour transport process mediated by vapour complexes of the LnCl 3AlCl 3 system

Mutual separations of rare earth chlorides in the PrEr, PrSm and PrNd binary systems and the PrGdEr ternary system were performed using chemical vapour transportation of vapour complexes LnAl n Cl 3+3 n , (Ln, rare earths). Heavier rare earth chlorides were more readily transported and concentrated in the deposits in lower temperature zones while lighter ones were selectively deposited in higher temperature zones. Good separation characteristics (efficiency and purity) were observed for the resulting LnCl 3 deposits by optimization of temperature gradients for the selective deposition of LnCl 3 and by repeating the transport reaction. The separation factors, expressed as atomic ratios for the resulting chlorides, Pr:Er and Pr:Sm, were equal to 10.8 and 2.3 respectively.

Kinetics of the exchange reactions and the formation rate of the lanthanide(III)-ethylenediamine-tetraacetate complexes

Kinetics of the exchange reactions and the formation rate of the lanthanide(III)-ethylenediamine-tetraacetate complexes

Susceptibility and Mössbauer studies of magnetic rare earth-iron-silicides

Ternary rare earth-iron-silicides of the Sc 2Fe 3Si 5 structure type have been studied by means of susceptibility measurements between 1.2 and 300 K and the Mössbauer effect at 4.2 K and room temperature. The compounds RE 2Fe 3Si 5 with RE = Gd—Er are antiferromagnetic with Néel temperatures below 11 K. Above 60 K, the susceptibilities follow a Curie- Weiss law with effective magnetic moments per RE atom approximately equal to the free ion values. 57Fe Mössbauer effect measurements of the above series and the superconductors forming with Sc, Y and Lu show quadrupole split spectra with small positive values of the isomer shift, indicating the absence of any magnetic moment at the iron site. There is no significant paramagnetic contribution to the 57Fe hyperfine field below the Néel temperature in the case of the antiferromagnetic compounds in applied fields up to 50 kG.

Crystal structures of some Ln 3Rh, Ln 7Rh 3 and LnRh 3 Phases

The Fe 3C-type structure occurs in the phases Nd 4Rh, Gd 3Rh, Y 3Rh and Er 3Rh. The atomic positional parameters in the Pnma space group are: 4Er in 4(c) 0.021, 0.250, 0.138 B 1 = 2.0 A ̊ 2 8Er in 8(d) 0.180, 0.061, 0.667 B 2 = 2.0 A ̊ 2 4Rh in 4(c) 0.389, 0.250, 0.937 B 3 = 0.5 A ̊ 2 Phases with the Ln 7Rh 3 stoichiometry in the GdRh, YRh and ErRh systems possess the Th 7Fe 3-type structure. The same structure occurs in the alloys of the light rare earths, La, Ce and Nd at the Ln 3Rh stoichiometry. Unlike LaRh 3 and NdRh 3, CeRh 3 crystallizes in the Cu 3Au-type structure. It is shown that electronic factors rather than the size factor play prominent roles in stabilizing these structures in the rare-earth alloys.

Disorder Resistivity of Binary Rare Earth Alloys

AbstractExpressions are derived for the disorder resistivity of binary rare earth alloys at temperatures above the magnetic transition point and at absolute zero. Only ferromagnetic alloys are considered. The treatment is based on a Nordheim approximation, extended to incorporate spin‐dependent scattering. The theoretical expressions are in satisfactory agreement with experimental data for Gd—Lu, Tb—Lu, Gd—Y and Gd—Er alloys.