Gd Atoms Research Articles

QUANTITATIVE PLANNING OF NEUTRON CAPTURE THERAPY ACCORDING TO THE KINETICS DATA OF Gd (III) COMPLEXES WITH MAGNETIC RESONANCE IMAGING

Neutron capture therapy (NCT) with thermal neutron beams of high flux density is the most promising method of therapy for inoperable malignant brain tumors using Gd in stable acetate complexes with possibility of visualization by magnetic resonance imaging (MRI). The effectiveness of NCT is determined by the maximum dose that is created in tumor cells by products of the capture of thermal neutrons by Gd atoms. Analyzing the kinetics of direct absorption and inverse diffusion of Gd complexes in brain tumor tissue by MRI, we were able to show that it is linear in all cases and Gd concentration in the tumor at the moment T is defined as С tum (Т) = k pl-tum ∙ ∫ С pl (t)∙exp(–k tum-pl (T–t))dt. At the same time, the value of the direct transport factor k plasma-tumor =5.87±0.31 is an order of magnitude higher than the rate of reverse diffusion k tumor-plasma =0.91±0.23. Then, according to the data of a single diagnostic dynamic study, it is possible to calculate the optimal regimen of Gd administration to achieve the therapeutic effect of a neutron beam of known flux density for NCT, while avoiding the release of Gd in healthy tissues.

Magnetic Properties and Magnetocaloric Effect of Nd<sub>0.7</sub>Gd<sub>0.3</sub>Mn<sub>2</sub>Si<sub>2</sub> Alloy

In this work, crystal structure, magnetic properties and magnetocaloric effect of Nd0.7Gd0.3Mn2Si2 alloy were studied by X-ray diffraction (XRD), Physical Property Measurement System (PPMS) and Differential Scanning Calorimetry (DSC). Nd0.7Gd0.3Mn2Si2 crystallizes in ThCr2Si2-typed structure with space group I4/mmm, in which the Nd, Gd, Mn and Si atoms occupy 2a (0, 0, 0), 2a (0, 0, 0), 4d (0, 1/2, 1/4) and 4e (0, 0, 0.38261) position, respectively. The Curie temperature (Tc) of Nd0.7Gd0.3Mn2Si2 alloy is 42 K, while the spin reorientation temperature (TSR) is 26 K and the Nel temperature (TN) is 410 K. The Tc and TN were determined using PPMS and DSC, respectively. The maximum value of the magnetic entropy change (-Smax) in the field change of 0-5 T is 11.862 J/kg K, while the value of relative cooling power (RCP) in Nd0.7Gd0.3Mn2Si2 alloy is 69.666 J/kg under the field change of 5 T.

Magnetocaloric effect over a wide temperature range in GdxHo3−xAl2 compounds with successive magnetic transitions

The GdxHo3−xAl2 (x = 0.5–2.5) compounds undergo two successive magnetic transitions: a second-order magnetic transition from paramagnetism (PM) to ferromagnetism (FM) around TC followed by a FM to ferrimagnetism (FIM)-like transition at Tt. The TC increases linearly with the increase of Gd content due to the de Gennes factor of Gd being larger than that of Ho, while the Tt remains nearly constant around 45 K independent of the variation of Gd content. The working temperature range is expanded by substituting Ho with Gd atoms due to the higher transition temperature of Gd3Al2 and the different composition dependence of successive magnetic transitions, and thus leading to an enhanced refrigerant capacity (RC). For a relatively low field change of 2 T, a giant RC value of 272 J/kg with a wide working temperature range of ∼80 K is obtained for x = 1.0 compound due to the partial overlap of successive ΔSM peaks. This is probably the largest RC value so far reported in the temperature range of liquid natural gas (111 K). Consequently, the large ΔSM and giant RC suggest that GdxHo3−xAl2 compounds could be good candidates of magnetic refrigerants in a wide temperature range.

Microstructural and magneto-transport properties of Bi1.6Pb0.4Sr2Ca1−xGdxCu2O8+δ superconducting ceramics

This study aims to investigate the effect of Gd doping on the phase formation, microstructure, transport and magnetic properties of the Bi(Pb)-2212 system. A series of superconducting bulks with a nominal composition of Bi1.6Pb0.4Sr2Ca1−xGdxCu2O8+δ with x=0, 0.05, 0.10 and 0.15 are synthesized by the solid state synthesis route. The formed samples are characterized by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), electrical transport and magnetic measurements. The experiment results reveal that all the samples doped are composed of Bi-2212 phase and traces of Bi-2201 secondary phase when compared to the undoped sample. The refinement of cell parameters shows that the doping reduces the cell volume of the samples. The texture degree decreases with doping while the degree of orthorhombicity increases. Quantitative EDS analysis confirms that Gd atoms are successfully introduced into crystalline structure. The SEM micrographs show randomly distributed grains with a flake-like shape. The highest value of onset critical transition temperatures is obtained for x=0.10 and is about 90.22K, which correlates well with the observed slope of resistivity and the hole concentration of the CuO2 layers. Magnetic hysteresis loops suggest that the diamagnetism, remanant magnetization and lower critical field are better for x=0.10. Based on the enhancements of both grain boundary weak-links and flux pinning centers, improvement of the critical current densities and flux pinning density is obtained with this kind of doping.

Growth, morphology, and structure of a monolayer thickGdFe2surface alloy

The growth and structure of an ordered ${\mathrm{GdFe}}_{2}$ surface alloy deposited on Mo(110) has been studied using in situ surface x-ray diffraction. Growth curves and reflectivity scans of varying ratios of Gd to Fe show how the two species intermix prior to alloy formation. After annealing to form the ordered surface alloy, in-plane x-ray diffraction data indicate that the Fe atoms are laterally displaced along the [001] or $[00\overline{1}]$ direction by $0.16\ifmmode\pm\else\textpm\fi{}0.02$ \AA{} from the long bridge site positions. Out-of-plane crystal truncation rod analysis reveals that the Gd atoms lie $3.40\ifmmode\pm\else\textpm\fi{}0.09$ \AA{} above the Mo(110) bridge site, an expansion of 22% relative to the expected hard sphere distance. This is significantly larger than observed in previous studies of the growth of pure Gd on Mo(110). Simple geometric changes are not able to account fully for this expansion and we propose that hydrogen incorporation during alloy formation may also contribute.

Atomistic simulation of trivalent ions doped in the hexagonal LuMnO3 ferroelectric phase

The interatomic potentials for multiferroic hexagonal LuMnO3 (h-LMO) in its ferroelectric (FE) phase was obtained for empirical fitting procedure and applied to study the effects of a series of trivalent metal and rare-earth dopants on its structural and ferroelectric distortions. The potential parameters found accurately reproduce lattice parameters (error below 0.3%), interatomic distances, pressure effect on the lattice parameters, and tilting angles of the MnO5 polyhedron. We investigated doping at Mn, Lu1 and Lu2 atom sites. It was found that the doped Mn atom site is the most energetically advantageous site for both the metal (Al, Ga, Fe and Cr) and rare-earth (La, Nb, Sm, Eu, Gd, Ho, Er, Yb, Y and Sc) atoms studied. The M-O3/O4 distances decrease when the Mn3+ ion site is doped by trivalent metal ions. The effects on the FE distortion of the material under doping and changes in the tilting angle of the M/MnO5 polyhedron were analyzed.

Magnetocrystalline anisotropy in Gd(Co,Fe)12B6: A first-principles study

The electronic structure, preferential site occupancy for Fe, and magnetocrystalline anisotropy (MCA) have been investigated in Gd(Co12−xFe)xB6via a DFT (density functional theory) plus Hubbard U approach (DFT + U). For Gd atoms, the spin-up 4f bands are fully occupied while the spin-down 4f hole levels are completely empty. The d-like states dominate at the Fermi Level, mainly contributed by Co(Fe) 3d electrons. Co atoms in GdCo12B6 carry magnetic moments of − 0.3 μB and − 0.7 μB at the 18g and 18h sites respectively, while the 7.3 μB Gd moments are ordered antiparallel to the Co(Fe) sublattice. The DFT total energy calculations show that the Fe atoms prefer to replace Co at the 18h site rather than the 18g site, with an energy gain of 0.16 eV/f.u. and they carry a magnetic moment of 1.5 μB/Fe. GdCo12B6 shows a weak easy c− axis MCA (Emca = 90 μeV/f.u.) while GdCo11FeB6 displays a moderate easy ab− plane MCA (Emca = −2690 μeV/f.u.). The spin reorientation induced by Fe doping is related to the electronic structure change near Fermi Level and the different contributions of Co and Fe to the MCA in GdCo12−xFexB6.

The role of atomic scale segregation in designing highly ductile magnesium alloys

Two solid solution binary magnesium-rare earth (RE) alloys, Mg-1wt.% Gd and Mg-1wt.% Dy were subjected to large strain hot rolling followed by recrystallization annealing at different temperatures for 60 min. Recrystallization and grain growth in Mg-1Gd led to stepwise change in the deformation texture, highlighted by a complete disappearance of the basal texture component developed during rolling. In case of Mg-1Dy, texture changes upon annealing were less accentuated, characterized by gradual softening of the deformation basal texture with increasing annealing temperatures. The development of favorable RE-textures during annealing is believed to be a result of solute segregation to planar defects, such as grain boundaries. It was observed using atom probe tomography that Gd atoms show a much higher grain boundary segregation tendency than Dy atoms. The enhanced segregation behavior of Gd manifests during annealing into a strong growth advantage of recrystallized off-basal orientations over basal orientations originating from the deformation microstructure, continuing as discontinuous grain growth at higher annealing temperatures and longer durations. No distinctive growth advantage was witnessed during recrystallization and grain growth of Mg-1Dy. Different segregation effects between the two RE elements and the resulting annealing texture evolution strongly impacted the room temperature tensile ductilities of both alloys. Mg-1Gd seemed to exhibit concomitant precipitation hardening effects, thereby displaying higher tensile strength along with enhanced ductilities. This work demonstrates the exciting possibility of being able to selectively exploit grain boundary characteristics using RE elements as an effective mechanism to tailor the microstructure during thermomechanical processing, thereby improve the mechanical performance of Mg alloys.

Structures, and luminescence and magnetic properties of Ln(III) complexes bearing dibenzoylmethane ligand (Ln=Eu and Gd)

The single crystal structure, luminescence and magnetic susceptibility of Cs[Ln(DBM)4] and Ln(DBM)3(phen) (Ln=Eu and Gd, DBM=dimenzoylmethanto and phen=1,10-phenanthroine) were characterized in detail. A pentanuclear Eu(III) cluster with the formula, Eu5(DBM)10(OH)5, was obtained from Cs[Eu(DBM)4] in ethanol, while from Cs[Gd(DBM)4] in acetonitrile, a one-dimensional polymeric Gd(III) assembly with the formula, {Cs[Gd(DBM)4]}n, was achieved via a heterobimetallic backbone, composed of alternating Cs and Gd atoms bridged by DBM. Exciting the Eu(III) complexes with near-UV light produced sensitized red emission by energy transfer from the triplet excited state of DBM to the Eu(III) ion. Replacing DBM by phen increased the quantum yield from Q=8.3% for Cs[Eu(DBM)4] to Q=16.6% for Eu(DBM)3(phen). This was attributed to a reduction in the site-symmetry of Eu(III) from D4h to C2v. The magnetic susceptibilities of the synthesized Ln(III) complexes in the crystalline or powder states were measured using a SQUID magnetometer. The Eu(III) complexes illustrated magnetic anisotropy at low temperatures and temperature-dependent susceptibilities. The coercive field inducing the magnetic anisotropy of Eu5(DBM)10(OH)5 was more than 40-fold stronger than those of Cs[Eu(DBM)4] and Eu(DBM)3(phen). In particular, the calculation based on the Van Vleck׳s treatment confirmed that the thermal mixing between the excited and ground states played a key role in the temperature-dependent susceptibilities of Eu(III). The magnetic susceptibility of the Gd(III) ion in Gd(DBM)3(phen) was identical to that of the free Gd(III) ion, wheras that of the Gd(III) ion in Cs[Eu(DBM)4] was higher. The phen ligand with the π-conjugate rigid planar structure decreased the magnetic susceptibilities of the Eu(III) and Gd(III) ions.

High Temperature Ferromagnetism in a GdAg2 Monolayer.

Materials that exhibit ferromagnetism, interfacial stability, and tunability are highly desired for the realization of emerging magnetoelectronic phenomena in heterostructures. Here we present the GdAg2 monolayer alloy, which possesses all such qualities. By combining X-ray absorption, Kerr effect, and angle-resolved photoemission with ab initio calculations, we have investigated the ferromagnetic nature of this class of Gd-based alloys. The Curie temperature can increase from 19 K in GdAu2 to a remarkably high 85 K in GdAg2. We find that the exchange coupling between Gd atoms is barely affected by their full coordination with noble metal atoms, and instead, magnetic coupling is effectively mediated by noble metal-Gd hybrid s,p-d bands. The direct comparison between isostructural GdAu2 and GdAg2 monolayers explains how the higher degree of surface confinement and electron occupation of such hybrid s,p-d bands promote the high Curie temperature in the latter. Finally, the chemical composition and structural robustness of the GdAg2 alloy has been demonstrated by interfacing them with organic semiconductors or magnetic nanodots. These results encourage systematic investigations of rare-earth/noble metal surface alloys and interfaces, in order to exploit them in magnetoelectronic applications.

On the role of Ag in enhanced age hardening kinetics of Mg–Gd–Ag–Zr alloys

The addition of Ag to the age hardenable Mg–Gd–Zr alloy system dramatically enhances early stage age hardening kinetics. Using atom probe tomography (APT), Ag-rich clusters were detected in a Ag-containing Mg–Gd–Zr alloy immediately after solution treatment and water quenching. During subsequent isothermal ageing at 200 °C, a high density of basal precipitates was observed during the early stages of ageing. These basal precipitates were enriched with Ag and Gd, as confirmed by APT. It is posited that Ag-rich clusters in the context of quenched-in vacancies can attract Gd atoms, increasing diffusion kinetics to facilitate the formation of the Ag + Gd-rich basal precipitates. The rapid formation of Ag + Gd-rich precipitates was responsible for accelerated ageing.

Di- and tetranuclear heterometallic 3d–4f cobalt(II)–lanthanide(III) complexes derived from a hexadentate bisoxime: Syntheses, structures and magnetic properties

Five heterometallic Co(II)–Ln(III) complexes, a discrete heterodinuclear complex [CoLLa(Py)(NO3)3(CH3OH)] (1) (Py=pyridine), a heterotetranuclear dimer [Co2L2La2(4,4′-bipy)(NO3)6(CH3OH)2] (2) (4,4′-bipy=4,4′-bipyridine) and three discrete heterodinuclear complexes [CoLLn(OAc)(NO3)2(CH3OH)] (Ln=Gd (3), Tb (4), Dy (5)), were synthesized with a hexadentate bisoxime ligand 1,2-bis(3-methoxysalicylideneaminooxy)ethane (H2L), and characterized by single crystal X-ray diffraction. The complexes 1, 3, 4 and 5 are discrete heterodinuclear structures, but the assembly of two dinuclear units [CoLLa(NO3)3(CH3OH)] and one 4,4′-bipyridine results in a discrete heterotetranuclear dimer 2. The Co(II) and La(III) atoms in the complexes 1 and 2 are penta- and decacoordinated, while the Co(II) and Ln(III) (Ln=Gd, Tb and Dy) atoms in the complexes 3, 4 and 5 are hexa- and nonacoordinated, respectively. Magnetic measurements were performed on the complexes 3, 4 and 5, where an intramolecular ferromagnetic interaction is found in the complex 3.

In silico study of the atomic and electronic structure of quantum dots of the CdTe family doped with atoms of rare earth elements

An in silico study of semiconductor quantum dots of the CdTe family doped with atoms of rare earth elements is performed based of density functional theory. An ab initio computer design of quantum dots based on CdTe nanoparticles doped with Eu и Gd atoms is carried out. Partial densities of states of CdTe:Eu and CdTe:Gd quantum dots are calculated and analyzed. X-ray absorption near edge (XANES) spectra near the Eu K-, L 1-, and L 3- and Gd K-, L 1-, and L 3-edges of CdTe:Eu and CdTe:Gd quantum dots are calculated. The sensitivity of XANES spectroscopy for the verification of parameters of a nanosized atomic structure of quantum dots based on CdTe particles doped with atoms of rare earth elements and the determination of the local atomic structure around the atoms of rare earth elements in quantum dots is demonstrated.

Hydrogenation induced structure and property changes in GdGa

Hydrides GdGaHx were obtained by exposing the Zintl phase GdGa with the CrB structure to a hydrogen atmosphere at pressures from 1.5 to 50bar and temperatures from 50 to 500°C. Structural analysis by powder X-ray diffraction suggests that conditions with hydrogen pressures in a range between 15 and 50bar and temperatures below 500°C afford a uniform hydride phase with the NdGaH1.66 structure (Cmcm, a=3.9867(7) Å, b=12.024(2) Å, c=4.1009(6) Å) which hosts H in two distinct positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by Gd atoms, whereas H2 atoms are inserted between Ga atoms. The assignment of the NdGaH1.66 structure is corroborated by first principles DFT calculations. Modeling of phase and structure stability as a function of composition resulted in excellent agreement with experimental lattice parameters when x=1.66 and revealed the presence of five-atom moieties Ga-H2-Ga-H2-Ga in GdGaH1.66. From in situ powder X-ray diffraction using synchrotron radiation it was established that hydrogenation at temperatures above 200°C affords a hydride with x≈1.3, which is stable up to 500°C, and that additional H absorption, yielding GdGaH1.66, takes place at lower temperatures. Consequently, GdGaH1.66 desorbs H above T=200°C. Without the presence of hydrogen, hydrides GdGaHx decompose at temperatures above 300°C into GdH2 and an unidentified Gd-Ga intermetallics. Thus the hydrogenation of GdGa is not reversible. From magnetic measurements the Curie-Weiss constant and effective magnetic moment of GdGaH1.66 were obtained. The former indicates antiferromagnetic interactions, the latter attains a value of ~8 μB which is typical for compounds containing Gd3+ions.

Fotoelektronna emisiya katoda Si–Gd–O

Electronic and emission properties of photocathodes fabricated on the basis of multilayered structures of oxidized Gd atoms deposited on the Si(100) surface and additionally covered with fresh layers of Gd atoms have been studied as functions of the structure holding time under vacuum, by using the methods of photoelectron (ℎv = 1.9÷10.2 eV) and Auger electron spectroscopies. It is found that, although the photocathode work function is equal to about 0.5 eV at some research stages, the photoemission is registered only at ℎv ≥ 2.8 eV. The analysis of the results allowed us to propose a model for the energy structure of the photocathode that agrees with experimental data. According to this model, the near-surface region of a photocathode, about 1 nm in thickness, consists of Gd2O3 with the energy gap width of about 5.3 eV. The distance from the Fermi level to the conduction band bottom equals about 2.7 eV in the Gd2O3 bulk. In the forbidden gap below the Fermi level, the bulk states and filled surface states associated with structural defects. A complicated dipole layer appears on the surface, and this gives the substantial reduction of the work function.

Carrier-dependent magnetic anisotropy of Gd-adsorbed graphene

Using first-principles calculation based on density functional theory, we study the magnetic anisotropy of Gd-adsorbed graphene and its dependence on carrier accumulation. We show that carrier accumulation not only impacts the magnitude of magnetic anisotropy but also switches its sign. Hole accumulation enhances the perpendicular anisotropy up to ∼16 meV per Gd atom, while electron accumulation switches the anisotropy from perpendicular to in-plane direction. Moreover, we find that the first order perturbation of spin-orbit coupling interaction induces a pseudo-gap at Γ for the perpendicular magnetization, which leads to the the anomalous magnetic anisotropy for the neutral composite. Our findings pave the way for magneto-electric materials based on rare-earth-decorated graphene for voltage-controlled spintronics.

Magnetic properties of bimetallic clusters composed of Gd and transition metals

Gadolinium, a rare earth metal, is ferromagnetic, while Mn, a transition metal atom, is antiferromagnetic in the bulk phase. Clusters of these elements, however, share some common properties; both exhibit ferrimagnetic behavior and maintain magnetic moments close to their free atomic value. Using density functional theory and generalized gradient approximation for exchange and correlation, we have studied the magnetic properties of bimetallic clusters composed of Gd and Mn to see if they show unusual behavior. The coupling between Gd and Mn spins is found to be antiferromagnetic, while that between Mn atoms is ferromagnetic. Moreover, the bonding between Gd and Mn atoms is stronger than that between the Gd atoms or Mn atoms, thus enabling the possibility of creating more stable magnetic particles. A systematic study of the magnetic and binding properties of clusters composed of Gd atom and other transition metal atoms such as V, Sc, Ti, Cr, Fe, and Co is also carried out to probe the effect of 3d-orbital occupation on magnetic coupling.

Electric and magnetic properties of Al86Ni8R6 (R=Sm, Gd, Ho) alloys in liquid and amorphous states

Electrical resistivity and magnetic susceptibility of Al86Ni8Sm6, Al86Ni8Gd6 and Al86Ni8Ho6 alloys are studied in a wide temperature range including amorphous, crystalline and liquid states. The negative value of resistivity temperature coefficient in amorphous ribbons is explained by the structural separation starting much before the beginning of their crystallization. The effective magnetic moments per Gd and Ho atoms are found to be essentially lower than for R3+ ions. The results are discussed in supposition of directed bonds between rare earth and aluminum atoms.

Molecular beam epitaxy deposition of Gd2O3 thin films on SrTiO3 (100) substrate

Gd2O3 thin films are grown on the SrTiO3 (100) substrate by molecular beam epitaxy (MBE) deposition. X-ray diffraction (XRD) analysis, conventional transmission electron microscopy (TEM) and aberration-corrected scanning transmission electron microscopy (STEM) are performed to investigate the microstructure of deposited thin films. It is found that the as-deposited thin film possesses a very uniform thickness of ∼40nm and is composed of single cubic phase Gd2O3 grains. STEM and TEM observations reveal that Gd2O3 thin film grows epitaxially on the SrTiO3 (100) substrate with (001)Gd2O3//(100)STO and [110]Gd2O3//[001]STO orientations. Furthermore, the Gd atoms are found to diffuse into the SrTiO3 substrate for a depth of one unit cell and substitute for the Sr atoms near the interface.

Effect of Ga vacancy on the magnetism in GaN:Gd: First-principles calculation

In recent years, GaN doped with Gd (GaN:Gd) has attracted much attention due to its potential applications in spintronic devices since the high temperature ferromagnetism and the colossal magnetic moment were observed in GaN:Gd. However, the microscopic nature of ferromagnetism in GaN:Gd still is controversial. We investigate the crystal parameters, magnetic moment, formation energies, and electronic structures of the defect complexes formed by Gd and native Ga (or N) vacancies in GaN by using the first-principles method based on the density functional theory. The calculated results show that the energy band gap of GaN:Gd becomes indirect and its width becomes small compared with that of GaN. The lattice constants of GaN:Gd expand due to the larger ionic radius of Gd than that of Ga atom, while they shrink when the Gd atom and Ga vacancies coexist. In the case of the isolated Gd dopant, the Gd-4f electrons lead to a magnetic moment of about 7 B in GaN:Gd. For the defect complex, one Ga vacancy can introduce a magnetic moment of about 2 B, while N vacancy has little effect on the total magnetic moment. In addition, when we focus on the defect complex composed of Gd and five neighboring Ga vacancies, we find that the magnetic moment of per Gd atom and the total magnetic moment depend strongly on the concentration and position of Ga vacancies. When the Ga vacancies are distributed loosely near the Gd atom, the magnetic moment of Gd atom increases slightly, while for the closely-distributed Ga vacancies the Gd magnetic moment can be increased by 2 B. We infer that the interactions among Ga vacancies result in the large magnetic moment of Gd atom. It is also found that the formation energy is very small when the Ga vacancies are distributed thickly around the Gd atom in GaN:Gd. Our results are in qualitative agreement with the results from other studies (Thiess A et al. 2012 Phys. Rev. B 86 180401; Thiess A et al. 2015 Phys. Rev. B 92 104418), where Ga vacancies were proposed to tend to cluster in GaN:Gd and induce the large magnetic moment of Gd. Moreover, the effect of distance between the Gd atom and Ga vacancies on the Gd magnetic moment is also discussed. It is found that the Gd magnetic moment is relatively large when Ga vacancies are close to the Gd atoms.