Gd Compounds Research Articles

Electronic structure and spectral properties of RCuSi (R=Nd,Gd) compounds

We report a joint experimental and theoretical investigation of optical properties and electronic structure of NdCuSi and GdCuSi compounds. Optical characteristics have been studied employing ellipsometry in a spectral range 0.22–15μm. Spin-polarized calculations of the electronic structure have been performed using LSDA+U method accounting for electronic correlations in the 4f shell of rare earth elements. Additionally, we probe our electronic structures by calculating the interband optical conductivities and comparing them with spectral measurement. We find that all main features of the experimental curves have been qualitative interpreted using the calculated densities of states.

Temperature dependence of the local magnetic momment at a Cd impurity diluted in RZn (R = Gd, Tb and Dy) compounds

In this work we calculate the local magnetic moment and the related magnetic hyperfine field on a non-magnetic s–p (Cd) impurity diluted in RZn (R = Gd, Tb, and Dy) compounds and their temperature dependence. Both quantities have contributions from the d and f electrons of the rare Earth and from the charge difference between Zn and the impurity ions. We further adopt a functional integral approach in the static approximation to describe the d–d Coulomb interaction arising from the 5d rare Earth ions. The temperatures range from up to the critical temperatures TC of the compounds. Our self-consistent results are in good agreement with the available experimental data.

Self-assembly synthesis, structural features, reversible temperature-induced dehydration/hydration, and magnetic and luminescence properties of lanthanide(iii) compounds derived from 5-fluoronicotinic acid

A new series of eight lanthanide coordination compounds, namely [Ln(5-Fnic)3(H2O)3]2·2H2O (Ln = La (1), Pr (2), Nd (3), Eu (4), Gd (5), and Tb (6)), [Tm(5-Fnic)2(H2O)4]2[5-Fnic]2·2H2O (7), and [Eu(5-Fnic)2(phen)2(NO3)(H2O)]·2H2O (8) were generated by a hydrothermal self-assembly method in H2O from the corresponding lanthanide metal(III) nitrates, with 5-fluoronicotinic acid (5-FnicH) as the main building block, and an optional (for 8) 1,10-phenanthroline (phen) as an ancillary ligand. All the products (1–8) were fully characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, and powder and single-crystal X-ray diffraction analyses. Compounds 1–6 are isostructural and reveal neutral dilanthanide(III) molecular units, 7 is ionic and has a cationic Tm2 core, whereas 8 displays a mononuclear structure. Distinct crystal packing patterns driven by strong intermolecular hydrogen bonds were observed in 1–6, 7, and 8, resulting in the 0D → 3D (1–7) or 0D → 1D (8) extension of the structures into H-bonded networks; their topological analysis and classification were performed. Products 1 and 3–8 constitute the first La, Nd, Eu, Gd, Tb, and Tm coordination compounds derived from 5-fluoronicotinic acid. The magnetic properties of compounds 2, 3, 5, and 7 were investigated. Besides, products 4, 6, and 8 exhibit a reversible temperature-induced dehydration/hydration behavior, which also influences their solid state luminescence properties that were studied in detail. The intensity of the emission bands of the dehydrated samples greatly increases after thermal removal of water molecules and then returns back to the original level upon exposure to water. This reversible behavior is more pronounced in 8 given the additional presence of phenanthroline moieties.

Implications of magnetic and magnetodielectric behavior of GdCrTiO5

We have carried out dc magnetization, heat-capacity, and dielectric studies down to 2 K for the compound GdCrTiO5, crystallizing in orthorhombic Pbam structure, in which well-known multiferroics RMn2O5 (R = Rare-earths) form. The points of emphasis are: (i) The magnetic ordering temperature of Cr appears to be suppressed compared with that in isostructural Nd counterpart, NdCrTiO5. This finding on the Gd compound suggests that Nd 4f hybridization plays an uncommon role in the magnetism of Cr in contrast to a proposal long ago. (ii) Dielectric constant does not exhibit any notable feature below about 30 K in the absence of external magnetic field, but a peak appears and gets stronger with the application of external magnetic fields, supporting the existence of magnetodielectric coupling. (iii) The dielectric anomalies appear even near 100 K, which can be attributed to short-range magnetic-order. We also observe a gain in spectral weight below about 150 K in Raman spectra in the frequency range 150–400 cm−1, which could be magnetic in origin, supporting short-range magnetic order. It is of interest to explore whether geometrically frustration plays any role in the dielectric properties of this family, as in the case of RMn2O5.

A One Dimensional 3d–4f Heterometallic Chain Based on Gd3+ Nodes and Tetranuclear {Cr4(hdpta)2} Complex Ligands: Synthesis, Structure and Magnetic Properties

Assembly reaction of 1,3-diamino-2-hydroxy-propane-N,N,N′,N′-tetraacetic acid (H5hdpta), sodium acetate and Cr3+ ion at pH 6.7 in aqueous solution leads to the formation of Na[Cr2(hdpta)(Ac)2] (1). Single crystal X-ray analysis show that 1 bears a 3D (4,4)-connected lon framework based on mononuclear Na+ nodes and dinuclear [Cr2(hdpta)(Ac)2]− complex ligands in which two Cr3+ ions are chelated by one hdpta5− and also bridged by two acetate auxiliary ligands. Further assemble of 1 with Gd3+ ions give rise to [Gd(NO3)3(H2O)4][Cr4Gd(hdpta)2(OH)4(H2O)5]·(NO3)·32H2O (2). The [Cr4Gd(hdpta)2(OH)4(H2O)5]+ cation of 2 exhibit a 1D chain structure based on [Cr4(hdpta)2(OH)4]2− complex ligands and mononuclear Gd3+ nodes. [Cr4(hdpta)2(OH)4]2− has a tetranuclear {Cr4} rectangular metal skeleton. Detailed synthesis experiments indicate heating is a simple and effective way to activate the inert Cr3+ ions to prepare oxygen-bridged Cr–Ln heterometallic compounds. Magnetic studies reveal that compound 2 shows overall antiferromagnetic interaction. Stepwise synthesis of a Cr–Na compound based on dinuclear {Cr2} unit and a Cr–Gd compound bearing tetranuclear {Cr4} unit are presented.

Study of absorption parameters around the K edge for selected compounds of Gd

The K shell absorption jump ratios, jump factors, effective atomic numbers, and electron densities were derived from the measured total mass attenuation coefficient using an energy dispersive X‐ray fluorescence spectrometer for Gd2O3, Gd2(CO3)3H2O, Gd2(C2O4)3H2O, and Gd2(SO4)3 compounds. The total mass attenuation coefficients were measured in the X‐ray energy range from 39.52 to 57.14 keV in a transmission geometry utilizing the Kα2, Kα1, Kβ1, and Kβ2 X‐rays from different secondary source targets excited by the 59.54‐keV photons from an Am‐241 annular source and detected by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. The energy gap, ionization energy, electron affinity, and global electrophilicity parameters of oxide, sulfate, oxalate, and carbonate ions were calculated using density functional theory (B3LYP). The experimental results are discussed based on these parameters. Copyright © 2015 John Wiley & Sons, Ltd.

Optical and thermal properties of the EuLnCuS3 (Ln = La, Pr, Sm, Gd) compounds

We have studied the IR transmission of the EuLnCuS3 (Ln = La, Pr, Sm, Gd) compounds in the spectral range 400 to 4000 cm–1 and their thermal expansion in the temperature range 300–1450 K. The compounds have high IR transmission in the range 1800–3000 cm–1. The observed sharp changes in their thermal expansion coefficients are caused by phase transitions.

Pentanuclear 3d-4f Heterometal Complexes of M(II)3Ln(III)2 (M = Ni, Cu, Zn and Ln = Nd, Gd, Tb) Combinations: Syntheses, Structures, Magnetism, and Photoluminescence Properties.

A new family of pentanuclear 3d-4f heterometal complexes of general composition [Ln(III)2(M(II)L)3(μ3-O)3H](ClO4)·xH2O (1-5) [Ln = Nd, M = Zn, 1; Nd, Ni, 2; Nd, Cu, 3; Gd, Cu, 4; Tb, Cu, 5] have been synthesized in moderate yields (50-60%) following a self-assembly reaction involving the hexadentate phenol-based ligand, viz., N,N-bis(2-hydroxy-3-methoxy-5-methylbenzyl)-N('),N(')-diethylethylenediamine (H2L). Single-crystal X-ray diffraction analyses have been used to characterize these complexes. The compounds are all isostructural, having a 3-fold axis of symmetry that passes through the 4f metal centers. The [M(II)L] units in these complexes are acting as bis-bidentate metalloligands and, together with μ3-oxido bridging ligands, complete the slightly distorted monocapped square antiprismatic nine-coordination environment around the 4f metal centers. The cationic complexes also contain a H(+) ion that occupies the central position at the 3-fold axis. Magnetic properties of the copper(II) complexes (3-5) show a changeover from antiferromagnetic in 3 to ferromagnetic 3d-4f interactions in 4 and 5. For the isotropic Cu(II)-Gd(III) compound 4, the simulation of magnetic data provides very weak Cu-Gd (J1 = 0.57 cm(-1)) and Gd-Gd exchange constants (J2 = 0.14 cm(-1)). Compound 4 is the only member of this triad, showing a tail of an out-of-phase signal in the ac susceptibility measurement. A large-spin ground state (S = 17/2) and a negative value of D (-0.12 cm(-1)) result in a very small barrier (8 cm(-1)) for this compound. Among the three Nd(III)2M(II)3 (M = Zn(II), Ni(II), and Cu(II)) complexes, only the Zn(II) analogue (1) displays an NIR luminescence due to the (4)F(3/2) → (4)I(11/2) transition in Nd(III) when excited at 290 nm. The rest of the compounds do not show such Nd(III)/Tb(III)-based emission. The paramagnetic Cu(II) and Ni(II) ions quench the fluorescence in 2-5 and thereby lower the population of the triplet state.

Structural, electronic and optical properties of YNi4Si-type RNi4Si compounds (R = La and Gd): a new orthorhombic derivative of CaCu5 structure

The structural, electronic and optical properties of new YNi4Si-type RNi4Si (R = La and Gd) compounds are studied using full-potential augmented plane-wave method. To account better for the on-site f electron correlation, we adopted the Coulomb-corrected local spin density approximation (LSDA + U) exchange–correlation potential. Our optimized results of lattice parameters show good agreement to the previously reported experimental study. Analysis of the calculated band structure of LaNi4Si and GdNi4Si compounds demonstrates their metallic character. We found Ni-3d states mainly contribute to density of states from −5.0 eV to the Fermi level which is consistent with experiment and previously reported result by Kowalczyk et al. (J Magn Magn Mater 305:348–351, 2006), having hexagonal CaCu5 structure. Our calculated optical conductivity compares well with the experimental data and the results are analysed in the light of band-to-band transitions.

Crystal Structure, Magnetic and Electrical Properties of Compounds in the RCrMnO5 Family (R = Sm, Eu, Gd, Tb, Ho and Er) Synthesized Under High Oxygen Pressure

AbstractRCrMnO5 (R = Sm, Eu, Gd, Tb, Ho, and Er) were synthesized at high O2 pressures and 900–950 °C. Crystal structures were refined by using powder X‐ray diffraction (PXRD) and powder neutron diffraction (PND) for Tb, Ho, and Er compounds and PXRD for Sm, Eu and Gd compounds. All compounds were isostructural with RMn2O5. By using the bond‐valence model we found that (Cr/Mn)4+ mainly occupy the octahedral sites and (Cr/Mn)3+ occupy the pyramidal sites. Antisite disorder between octahedral and pyramidal sites was found in the three samples analyzed by PND. From the values obtained for the occupancies of Cr and Mn in the pyramidal and octahedral sites and from the approximate average oxidation states for each crystallographic site obtained by the bond‐valence calculations, an estimated ionic distribution model was proposed. The μeff value for RCrMnO5 could be explained by considering the contribution of all the paramagnetic species and by using the ionic distribution model. No magnetic long‐range order was observed by PND in R = Er, Ho, and Tb compounds. All the Curie–Weiss temperatures obtained from the magnetic susceptibility were negative (θ < 0), indicating antiferromagnetic correlations. For the compounds with Eu and Sm, θ close to –200 K were obtained for the Cr–Mn sublattice. The semiconducting properties could be described by a variable range hopping mechanism associated with antisite disorder of Cr/Mn. No dielectric transitions were observed in the electric permittivity in the measured temperature range.

Effect of size disorder on the structure and magnetic properties of La0.3R0.2Sr0.5Ti0.5Fe0.5O3 (R = La, Nd, Gd, and Dy) compounds

Successful preparation of perovskite oxides of chemical formula La0.3R0.2Sr0.5Ti0.5Fe0.5O3 (R = La, Nd, Gd, and Dy) has been achieved by citrate-gel precursor method, and their structures were determined using powder X-ray diffraction (XRD). The Rietveld analysis of the XRD data showed that all the samples have anti-site disorder. Anti-site disorder has not been seen to alter the symmetry of crystal structure but leads to tilt of the Fe3+ neighbouring octahedral which by its role gives rise to canted anti-ferromagnetism as a result of anti-parallel misalignment of the magnetic moments of the Fe3+ ions.

Investigation of structural, magnetic and electric transport properties of half-doped chromium manganites La0.3R0.2Sr0.5Mn0.5Cr0.5O3 (R=La, Nd, Sm, and Gd)

The effect of smaller rare-earth substitution in the La site of La0.5Sr0.5Mn0.5Cr0.5O3 has been investigated to elucidate how the properties of this material change with La doping. La0.3R0.2Sr0.5Mn0.5Cr0.5O3 (R=La, Nd, Sm, and Gd) compounds have been studied by X-ray diffraction and magnetic and transport measurements. All the samples were determined to be single phase and crystallized in an orthorhombic structure. Magnetic measurements showed that doping of smaller rare-earth ion for La decreases both Curie temperature (TC) and Weiss constant (Θ). Except R=La, all the phases follow Curie–Weiss law in the high temperature region. All the samples are semiconducting and the transport properties are dominated by the adiabatic small polaron hopping mechanism.

Manifestation of π–π Stacking Interactions in Luminescence Properties and Energy Transfer in Aromatically-Derived Tb, Eu and Gd Tris(pyrazolyl)borate Complexes

The three new complexes Tp(Py)Ln(CH3CO2)2(H2O) (Ln = Eu (1), Gd(2), or Tb (3)) were prepared and characterized crystallographically. In the crystal lattices of these complexes, separate molecules are connected in infinite chains by π-stacking interactions. Complexes 1 and 3 display intense photoluminescence and triboluminescence (red and green respectively), while compound 3 exhibits electroluminescence commencing at 9 V in an ITO/PVK/3/Al device (ITO = indium-tin oxide, PVK = poly(N-vinylcarbazole)). A series of Eu/Tb-doped Gd compounds was prepared by cocrystallization from mixtures of 1 and 2 or 2 and 3, respectively. It was shown that π-stacking interactions are involved in increasing the efficiency of energy transfer from the gadolinium complex to emitting [Tp(Py)Eu](2+) or [Tp(Py)Tb](2+) centers, and this energy transfer occurs through hundreds of molecules, resembling the process of energy harvesting in chloroplast stacks.

Characterization of Ferromagnetic Order in CePd2P2

We examine magnetic ordering in CePd2P2 by neutron-scattering experiment and confirmed a ferromagnetic order at low temperatures. From the neutron-scattering data, the ordered moment is evaluated to be ~ 1.3(3) μB per Ce ion at 3 K and is considered to be parallel to the c-axis. In addition, no evidence of the change in the magnetic structure was observed below TC within the experimental accuracy. In DC magnetization measurement with an as-grown powder sample and a magnetically aligned sample, a clear magnetic anisotropy in CePd2P2 was observed in both ferromagnetic and paramagnetic phases. To obtain further insight to the large Curie temperature TC of CePd2P2, we have examined the magnetic properties of GdPd2P2 as a reference material. In DC magnetization measurement, successive magnetic transitions at TI = 10.6 K and TII = 7.4 K were observed in GdPd2P2. By comparing the transition temperatures of the Ce and Gd compounds, we argue the origin of the large Curie temperature of CePd2P2.

Crystal structure and magnetic properties of GdSi1.78, Gd(Si0.684Ge0.316)1.78, GdGe1.57, and GdSn2 compounds

Intermetallic compounds of Gd with Si, Ge, and Sn near 1:2 stoichiometry adopt several closely related crystal structures. We find that GdSi1.78 and Gd(Si0.684Ge0.316)1.78 crystallize in the same GdSi1.4-type orthorhombic structure (space group Imma), while GdGe1.57 and GdSn2 adopt α-ThSi2-type tetragonal structure (space group I41/amd) and ZrSi2-type orthorhombic structure (space group Cmcm), respectively. All compounds order antiferromagnetically; their Néel temperatures are only weakly affected by the magnetic field of less than 50kOe. Unusual features are observed including multiple phase transitions and thermomagnetic irreversibilities.

Synthesis, structure, and luminescent properties of a novel binuclear Gd(III) compound

The compound [Gd2(PZDA)3(H2O)]n (I), where H2PZDA = 2,3-pyrazinedicarboxylic acid, was synthesized under hydrothermal conditions and characterized by elemental analysis, infrared spectrometry, thermogravimetric analysis and single crystal X-ray diffraction (CIF file CCDC no. 848802). In I, Gd(III) centers adopt eight-coordinated and nine-coordinated modes to construct distorted triangular dodecahedral and tricapped trigonal prism configurations, respectively. Three-dimensional (3D) structure of the compound is formed through C-H⋯π interactions and π-π stacking. Measurement of the luminescent property at room temperature shows that the as-synthesized compound presents good selectivity towards Pb2+ ion, suggesting that it may be promising potential as selective luminescent probes of Pb2+ ion.

Magnetic properties and magnetocaloric effect in the R2PdSi3 (R = Gd, Dy and Er) compounds

The magnetic properties and magnetocaloric effect in R2PdSi3 (R=Dy, Dy and Er) compounds have been investigated. All these compounds possess an antiferromagnetic (AFM)-paramagnetic (PM) transition around their respective Néel temperatures. And, it is found that the Dy2PdSi3 and Er2PdSi3 compounds undergo a spin-glass behavior below Néel temperature. Under the magnetic field change of 5T, the values of -ΔSMmax reach 11.8J/kgK for Gd2PdSi3, 16.6J/kgK for Dy2PdSi3 and 22J/kgK for Er2PdSi3, respectively. Especially, the values of -ΔSMmax in the Er2PdSi3 compound are 8 and 14.5J/kgK for field change of 1 and 2T, which is attributed to a field-induced metamagnetic transition from AFM to FM states. The large reversible -ΔSM and large RC together with the absence of thermal and field hysteresis indicate that Er2PdSi3 compound could be a promising candidate for magnetic refrigeration at low temperatures.

Magnetism and magnetocaloric effect in YNi 4 Si-type R Ni 4 Si ( R =Ce, Gd, Tb and Dy) compounds

Abstract Magnetic properties and magnetocaloric effect of YNi 4 Si-type R Ni 4 Si ( R =Ce, Gd, Tb and Dy) compounds have been investigated. Magnetic measurements indicate the intermediate valence state of cerium in YNi 4 Si-type CeNi 4 Si. The magnetocaloric effect of GdNi 4 Si, TbNi 4 Si and DyNi 4 Si are calculated in terms of isothermal magnetic entropy change and they reach maximum values of −22.9 J/kg K, −13.5 J/kg K and −15.6 J/kg K for a field change of 140 kOe near ~28 K, 47 K and 27 K and they show maximum values of −12.7 J/kg K, −7.8 J/kg K and −9.3 J/kg K for a field change of 50 kOe near ~28 K, 42 K and 22 K, respectively. In contrast to GdNi 4 Si, the magnetization-field isotherms for TbNi 4 Si and DyNi 4 Si exhibit hysteresis loop at 2 K due to strong magnetocrystalline anisotropy.

Magnetic and vibrational properties of Gd2(Mo0.9W0.1O4)3 and Gd1.8Er0.2(MoO4)3

Abstract In this work, we report on the analysis of both vibrational and magnetic properties of heavy rare-earth molybdates Gd 2 (Mo 0.9 W 0.1 O 4 ) 3 and Gd 1.8 Er 0.2 (MoO 4 ) 3 . The crystal structures, as determined by X-ray powder diffraction and the Rietveld refinement analysis, established that at room temperature both of these materials belong to orthorhombic Pba 2 space group. Magnetization measurements showed that no saturation is present up to 8 T at T =10 K, and the magnetic susceptibility curves show paramagnetic behavior down to T =10 K. The effective magnetic moments and possible short-range magnetic interactions between Gd 3+ ions are treated and discussed. Raman spectra of both of these molybdates are similar to that of the pure compound Gd 2 (MoO 4 ) 3 , indicating that changes in the Raman spectra due to the introduction of either Er or W doping are negligible at the subject dopant concentrations.

Theoretical studies of strongly correlated rare-earth intermetallics RIn3 and RSn3 (R = Sm, Eu, and Gd)

In this paper, the structural, elastic, and electronic properties of RIn3 and RSn3 (R = Sm, Eu, Gd) compounds have been investigated using the full potential linearized augmented plane wave plus local orbital method within the density functional theory. The structural properties are investigated using the LDA, GGA, and the band correlated LDA+U and GGA+U schemes. The lattice parameters are in good agreement with the available experimental results and the divalent state of Eu is also verified. The spin-orbit coupling is included in order to predict the correct electronic properties and splitting of 4f states of the rare earth elements is also incorporated. We calculated Bulk modulus, shear modulus, Young's modulus, anisotropic ratio, Kleinman parameters, Poisson's ratio, Lame's co-efficient, sound velocities for shear and longitudinal waves, and Debye temperature. We also predict the Cauchy pressure and B/G ratio in order to explore the ductile and brittle behaviors of these compounds.