Rare-earth Systems Research Articles

Strain-mediated ion–ion interaction in rare-earth-doped solids

It was recently shown that the optical excitation of rare-earth ions produces a local change of the host matrix shape, attributed to a change of the rare-earth ion’s electronic orbital geometry. In this work we investigate the consequences of this piezo-orbital backaction and show from a macroscopic model how it yields a disregarded ion–ion interaction mediated by mechanical strain. This interaction scales as , similarly to the other archetypal ion–ion interactions, namely electric and magnetic dipole–dipole interactions. We quantitatively assess and compare the magnitude of these three interactions from the angle of the instantaneous spectral diffusion mechanism, and re-examine the scientific literature in a range of rare-earth doped systems in the light of this generally underestimated contribution.

Monitoring System of Rare Earth Electrolysis Equipment Based on OPC UA Technology

A set of rare earth electrolysis equipment monitoring systems based on OPC unified architecture is proposed given the complex environment of the rare earth electrolysis workshop, the difficulty of data acquisition, and the interconnection between equipment. The monitoring client of rare earth electrolysis equipment based on OPC UA communication protocol is designed and developed with C # language. The connection between the OPC UA server and the monitoring system is realized, and the data acquisition and real-time monitoring of the running state of the electrolysis equipment are completed. The primary goal of the rare earth electrolysis field equipment is to acquire and monitor rare earth electrolysis process current, voltage, and other internal state data in real-time.

Rational Design of a Rare-Earth Oxychalcogenide Nd3 [Ga3 O3 S3 ][Ge2 O7 ] with Superior Infrared Nonlinear Optical Performance.

Inorganic chalcogenides have been studied as the most promising infrared (IR) nonlinear optical (NLO) candidates for the past decades. However, it is proven difficult to discover high-performance materials that combine the often-incompatible properties of large energy gap (Eg ) and strong second harmonic generation (SHG) response (deff ), especially for rare-earth chalcogenides. Herein, centrosymmetric Cs3 [Sb3 O6 ][Ge2 O7 ] is selected as a maternal structure and a new noncentrosymmetric rare-earth oxychalcogenide, namely, Nd3 [Ga3 O3 S3 ][Ge2 O7 ], is successfully designed and obtained by the module substitution strategy for the first time. Especially, Nd3 [Ga3 O3 S3 ][Ge2 O7 ] is the first case of breaking the trade-off relationship between wide Eg (>3.5eV) and large deff (>0.5 × AgGaS2 ) in rare-earth chalcogenide system, and thus displays an outstanding IR-NLO comprehensive performance. Detailed structure analyses and theoretical studies reveal that the NLO effect originates mainly from the cooperation of heteroanionic [GaO2 S2 ] and [NdO2 S6 ] asymmetric building blocks. This work not only presents an excellent rare-earth IR-NLO candidate, but also plays a crucial role in the rational structure design of other NLO materials in which both large Eg and strong deff are pursued.

Sol-gel based synthesis to explore structure, magnetic and optical properties of double perovskite Y2FeCrO6 nanoparticles

In this present investigation, nanoparticles of B-site disordered Y2FeCrO6 (YFCO) double perovskite have been successfully synthesized for the first time by optimizing synthesis steps and temperatures of facile sol-gel technique to investigate their structural, magnetic, and optical properties. The Rietveld refinement of the X-ray diffraction pattern of YFCO nanoparticles revealed a single-phase orthorhombic structure with pbnm space group. The average size of the nanoparticles is around 67±15 nm determined by both field emission scanning electron microscopy and transmission electron microscopy imaging. The existence of mixed valence states of Fe and Cr ions was confirmed by X-ray photoelectron spectroscopy which is an indication of the absence of proper B site long range ordering. The temperature dependent magnetization curves demonstrated negative magnetization of this double perovskite material with compensation temperature at around 170 K. The field-dependent magnetic hysteresis loops exhibited the coexistence of weak ferromagnetic and antiferromagnetic domains in YFCO nanoparticles. The exchange bias effect was observed below Néel temperature which is tunable by a cooling magnetic field. The UV–visible spectroscopy ensured that YFCO nanoparticles have a direct band gap of ∼ 1.90 eV, which was further confirmed by steady-state photoluminescence spectroscopy. This B-site disordered YFCO might enhance interest on basic fundamental research on disordered rare-earth and transition metal-based perovskite systems and can be used for spintronics as well as photocatalytic applications because of its favorable magnetic and optical properties.

Controlling the electronic and magnetic properties of ZnO monolayer by rare-earth atoms substitutional doping

In this article, the structural, electronic, and magnetic properties of rare-earth (RE) atoms substitutional doping in the ZnO monolayer have been studied by DFT + U. The relaxed structures of RE-doped (RE = La, Ce, Pr, Nd, Pm, Sm and Eu) ZnO monolayer present a distortion of the environment while the calculated formation energies reveal that the substitutional doping of considered rare-earth atoms in ZnO monolayer are possible. The results show that the local spin magnetic moments of La-, Ce-, Pr-, Nd-, Pm-, Sm-, and Eu-doped systems are 0, 1.26, 3.06, −4.05, 5.06, 6.06, 7.08 μB, respectively, which are proportional to the number of spin-parallel 4f electrons. The electronic structure calculations reveal that the La-doped system becomes conductor, while other doping systems are still semiconductors. These results suggest that ZnO monolayer with rare-earth substitutional doping systems have potential values in spintronic applications and the development of magnetic nanostructures.

Norm-Conserving 4f-in-Core Pseudopotentials and Basis Sets Optimized for Trivalent Lanthanides (Ln = Ce–Lu)

We present here a set of scalar-relativistic norm-conserving 4f-in-core pseudopotentials, together with complementary valence-shell Gaussian basis sets, for the lanthanide (Ln) series (Ce-Lu). The Goedecker, Teter, and Hutter (GTH) formalism is adopted with the generalized gradient approximation (GGA) for the exchange-correlation Perdew-Burke-Ernzerhof (PBE) functional. The 4f-in-core pseudopotentials are built through attributing 4f-subconfiguration 4fn (n = 1-14) for Ln (Ln = Ce-Lu) into the atomic core region, making it possible to circumvent the difficulty of the description of the open 4fn valence shell. A wide variety of computational benchmarks and tests have been carried out on lanthanide systems including Ln3+-containing molecular complexes, aqueous solutions, and bulk solids to validate the accuracy, reliability, and efficiency of the optimized 4f-in-core GTH pseudopotentials and basis sets. The 4f-in-core GTH pseudopotentials successfully replicate the main features of lanthanide structural chemistry and reaction energetics, particularly for nonredox reactions. The chemical bonding features and solvation shells, hydrolysis energetics, acidity constants, and solid-state properties of selected lanthanide systems are also discussed in detail by utilizing these new 4f-in-core GTH pseudopotentials. This work bridges the idea of keeping highly localized 4f electrons in the atomic core and efficient pseudopotential formalism of GTH, thus providing a highly efficient approach for studying lanthanide chemistry in multi-scale modeling of constituent-wise and structurally complicated systems, including electronic structures of the condensed phase and first-principles molecular dynamics simulations.

Slow Relaxation of Magnetization in a p-Semiquinone Radical-Bridged Dysprosium Complex

The syntheses and magnetic properties of the first family of p-semiquinone-radical-bridged lanthanide complexes with crystal structures, sharing formula {Ln[(QMe4)•–Cl2(THF)3]}2·solvent (Ln = Tb, Dy, Ho, Er, Tm and Yb; H2QMe4 = 2,3,5,6-tetramethylhydroquinone), are reported. The semiquinone-radical motif is formed by oxidizing hydroquinone with FeCl3 instead of reducing quinone with only variable-valence lanthanide ions and is therefore applicable to most rare-earth systems. The Dy(III) analogue exhibits a two-step slow relaxation of magnetization behavior under an applied magnetic field, being the first lanthanide p-semiquinone single-molecule magnet.

Crystal structure, chemical bond characteristics, infrared reflection spectrum, and microwave dielectric properties of Nd 2(Zr 1− x Ti x ) 3(MoO 4) 9 ceramics

Microwave dielectric ceramics (MWDCs) with low dielectric constant and low dielectric loss are desired in contemporary society, where the communication frequency is developing to high frequency (sub-6G). Herein, Nd₂(Zr_1−<i>x</i>Ti_<i>x</i>)₃(MoO₄)₉ (NZ_1−<i>x</i>T_<i>x</i>M, <i>x</i> = 0.02–0.10) ceramics were prepared through a solid-phase process. According to X-ray diffraction (XRD) patterns, the ceramics could form a pure crystal structure with the <i>R</i><inline-formula> <math display="inline" id="MA1"><mover accent="true"><mn>3</mn><mo>¯</mo></mover></math></inline-formula><i>c</i> (167) space group. The internal parameters affecting the properties of the ceramics were calculated and analyzed by employing Clausius–Mossotti relationship, Shannon’s rule, and Phillips–van Vechten–Levine (P–V–L) theory. Furthermore, theoretical dielectric loss of the ceramics was measured and analyzed by a Fourier transform infrared (IR) radiation spectrometer. Notably, when <i>x</i> = 0.08 and sintered at 700 ℃, optimal microwave dielectric properties of the ceramics were obtained, including a dielectric constant (<i>ε</i>_r) = 10.94, <i>Q</i>·<i>f</i> = 82,525 GHz (at 9.62 GHz), and near-zero resonant frequency temperature coefficient (<i>τ</i>_<i>f</i>) = −12.99 ppm/℃. This study not only obtained an MWDC with excellent properties but also deeply analyzed the effects of Ti⁴⁺ on the microwave dielectric properties and chemical bond characteristics of Nd₂Zr₃(MoO₄)₉ (NZM), which laid a solid foundation for the development of rare-earth molybdate MWDC system.

Laser-induced Fano asymmetry, electron-phonon coupling, and phase transition in lanthanide sesquioxide (Ln2O3; Ln = Eu, Gd, Dy) nanoparticles: A Raman spectroscopic investigation

Laser power-dependent Raman spectroscopy is deployed to probe Fano interference in asymmetrically broadened Tg modes and the associated line shift in three technologically sound, meticulously characterized rare-earth sesquioxide systems. Group theoretical analysis is accompanied to introspect the Raman-active optic modes in cubic, monoclinic, and trigonal phases and identify the laser heating-induced local phase transitions. With increasing laser intensity, a regular redshift and larger negative asymmetry in the Raman peaks are detected, which is attributed to moderations in Fano scattering by enhanced electron–phonon coupling amid the focussed photoexcited electron plasma and is illustrated using a Feynman diagram. A quantitative study is thereby performed to unveil the intrinsic nature of discrete-continuum Fano resonance in the nanoparticles of interest emphasizing the high sensitivity of Raman spectra to the excitation strength that perturbs the generic vibrational features at the Brillouin zone center by influencing the interference conditions, force constant, and length of the associated bonds compelled by tensile stress. A rising trend of the charge–phonon coupling constant (λ) with laser power validates a stronger particle–quasiparticle coupling, whereas a shorter anharmonic phonon lifetime (τanh) indicates faster interactions. Using Allen's formalism, the charge density of states [N(εF)] at the Fermi level per spin and molecule is calculated, which pertains to a negative regression dependence in the λN(εF)−τanh dynamics.

Non-Fermi liquid behavior and quantum criticality in cubic heavy fermion systems with non-Kramers multipolar local moments

Notable non-Fermi liquid and quantum critical behaviors are observed in rare-earth metallic systems with non-Kramers local moments supporting a number of different multipolar moments. A prominent example is $\text{Pr(Ti,V)}_{2}\text{Al}_{20}$, where the non-Kramers doublet of the $\text{Pr}^{3+}$ ion allows quadrupolar and octupolar moments, but lacks a dipolar moment. Previous theoretical studies show that a single impurity Kondo problem with such an unusual local moment leads to novel non-Fermi liquid states. In this work, we investigate possible quantum critical behaviors arising from the competition between non-Fermi liquid states and multipolar-ordered phases induced by the RKKY interaction. We consider a local version of the corresponding Kondo lattice model, namely the Bose-Fermi Kondo model. Here, the multipolar local moments are coupled to fermionic and bosonic bath degrees of freedom representing the multipolar Kondo effect and RKKY interactions. Using a perturbative renormalization group (RG) study up to two loop order, we find critical points between non-Fermi liquid Kondo fixed points and a quadrupolar ordered fixed point. The critical points describe quantum critical behaviors at the corresponding phase transitions and can be distinguished by higher order corrections in the octupolar susceptibility that can be measured by ultrasound experiments. Our results imply the existence of a rich expansion of the phases and quantum critical behaviors in multipolar heavy fermion systems.

Probing laser-induced spin-current generation in synthetic ferrimagnets using spin waves

Several rare-earth transition-metal ferrimagnetic systems exhibit all-optical magnetization switching upon excitation with a femtosecond laser pulse. Although this phenomenon is very promising for future opto-magnetic data storage applications, the role of non-local spin transport in these systems is scarcely understood. Using Co/Gd and Co/Tb bilayers we isolate the contribution of the rare-earth materials to the generated spin currents by using the precessional dynamics they excite in an adjacent ferromagnetic layer as a probe. By measuring THz standing spin-waves as well as GHz homogeneous precessional modes, we probe both the high- and low-frequency components of these spin currents. The low-frequency homogeneous mode indicates a significant contribution of Gd to the spin current, but not from Tb, consistent with the difficulty in achieving all-optical switching in Tb-containing systems. Measurements on the THz frequency spin waves reveal the inability of the rare-earth generated spin currents to excite dynamics at the sub-ps timescale. We present modelling efforts using the $s$-$d$ model, which effectively reproduce our results and allow us to explain the behavior in terms of the temporal profile of the spin current.

Systematic study of electronic states of Ln(O,F)BiS2 by spin- and angle-resolved photoemission spectroscopy

The evolution of fine electronic structures in superconducting $\mathrm{Ln}{\mathrm{O}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}\mathrm{Bi}{\mathrm{S}}_{2}$ (Ln denotes lanthanoid) is systematically investigated with spin- and angle-resolved photoemission spectroscopy. A shape change of the Fermi surface (FS) at the $X$ point from elliptical to rectangular with increasing the electron doping is commonly observed in different lanthanide systems. Besides that, an emergent large Fermi surface around the \cyrchar\CYRG{} point is also observed in all the samples with different doping levels deviating from the theoretical prediction, which might be related to the superconductivity. In addition, we found a humped band around $X$(\ensuremath{\pi},0) in the highly doped samples only, which may be attributed to the ${\mathrm{BiS}}_{2}$ surface reconstruction or surface defects relying on the electron concentration. We also demonstrate the spin-selective excitation of photoelectrons, which indicates the presence of spin-orbital-entangled bulk Rashba splitting in this system. This result may enable the optical tuning of electron spin in a ${\mathrm{BiS}}_{2}$-based system.

Magnetocaloric effect in ScGdTbDyHo high-entropy alloy: Impact of synthesis route

Magnetic energy conversion systems based on magnetocaloric effect promise to be an efficient and eco-friendly alternative to widespread gas cooling systems. Progress in this field initiates an active search for high-performance magnetic refrigerants with suitable characteristics. Among various caloric materials, rare-earth multi-principal element alloys are of particular interest to achieve these purposes. Since structure and properties in these materials strongly depend on synthesis conditions and fabrication prehistory, these issues need to be considered for each multi-element systems. This study is aimed to address structure formation, magnetic and magnetocaloric properties in ScGdTbDyHo high-entropy alloy fabricated under different conditions. We analyze the liquid and solid phases in this system using the ab initio molecular dynamics simulations and find that the alloy has a strong tendency to form a single-phase solid solution. Within the experimental study, as-cast, rapidly quenched, thermally annealed and severely cold-deformed alloy samples have been examined. We have found that all the fabricated specimens are single-phase hexagonal close-packed solid solutions characterized by different density of structural defects. The magnetic measurements reveal a complex magnetic structure in these materials. The Neel point in the studied alloys varies in the range of 139–144 K. A field-induced metamagnetic transition from antiferromagnetic to ferromagnetic state is observed in the alloy samples at all temperatures below the Neel point. In the magnetically ordered state, all the materials demonstrate large coercive force, reaching 4 kOe. Despite of the magnetic hysteresis, the alloys demonstrate the largest values of relative cooling power (920–984 J/kg at 5 T magnetic field) among similar rare-earth high-entropy systems reported so far. Analysis of the experimental results obtained for the alloy samples fabricated under different synthesis conditions allows us to conclude that there is a correlation between structural defectiveness and refrigerant capacity in this rare-earth system.

Interface bonding and mechanical properties of copper/graphene interface doped with rare earth elements: First principles calculations

The interface doping with rare earth elements is a novel strategy to enhance the weak interface bonding of copper-graphene system (Cu-G). In this work, taking Sc, Y, La as representatives, we investigated the structural, electronic and mechanical properties of clean and doped Cu-G systems using first principles calculations. By the comparison of interface spacing and work of separation with clean system, the significantly improved interface interaction in rare earth elements doped systems has been verified. Besides, difference charge density, Bader charge and density of states were employed to reveal the microscopic modifying mechanism on the atomic scale. Then, the tensile stress-strain curves were obtained using a fitting function related with the element electronegativity, and thus the quantitative relationship between the interface bonding and mechanical properties was determined, which could provide theoretical guidance for the interface modification of Cu-G composites through doping rare earth elements.

Quantum error correction in the noisy intermediate-scale quantum regime for sequential quantum computing

We use density-matrix simulations to study the performance of three distance three quantum error correction (QEC) codes in the context of the rare-earth (RE) ion-doped crystal platform for quantum computing. We analyze pseudothresholds for these codes when parallel operations are not available, and examine the behavior both with and without resting errors. In RE systems, resting errors can be mitigated by extending the system's ground-state coherence time. For the codes we study, we find that if the ground-state coherence time is roughly 100 times larger than the excited-state coherence time, resting errors become small enough to be negligible compared to other error sources. This leads us to the conclusion that beneficial QEC could be achieved in the RE system with the expected gate fidelities available in the noisy intermediate-scale quantum regime. However, for codes using more qubits and operations, a factor of more than 100 would be required. Furthermore, we investigate how often QEC should be performed in a circuit. We find that for early experiments in RE systems, the minimal $[[5,1,3]]$ would be most suitable as it has a high threshold error and uses few qubits. However, when more qubits are available the $[[9,1,3]]$ surface code might be a better option due to its higher circuit performance. Our findings are important for steering experiments to an efficient path for realizing beneficial quantum error correcting codes in early RE systems where resources are limited.

Quantum Yu-Shiba-Rusinov dimers

Magnetic adatoms on a superconducting substrate undergo a quantum phase transition as their exchange coupling to the conduction electrons increases. For quantum spins, this transition is accompanied by screening of the adatom spin. Here, we explore the consequences of this screening for the phase diagrams and subgap excitation spectra of dimers of magnetic adatoms coupled by hybridization of their Yu-Shiba-Rusinov states and spin-spin interactions. We specifically account for higher spins, single-ion anisotropy, Ruderman-Kittel-Kasuya-Yosida coupling, and Dzyaloshinsky-Moriya interactions relevant in transition-metal and rare-earth systems. Our flexible approach based on a zero-bandwidth approximation provides detailed physical insight and is in excellent qualitative agreement with available numerical-renormalization group calculations on monomers and dimers. Remarkably, we find that even in the limit of large impurity spins or strong single-ion anisotropy, the phase diagrams for dimers of quantum spins remain qualitatively distinct from phase diagrams based on classical spins, highlighting the need for a theory of quantum Yu-Shiba-Rusinov dimers.

Thermally Activated Photophysical Processes of Organolanthanide Complexes in Solution.

The effect of temperature upon the lanthanide luminescence lifetime and intensity has been investigated in toluene solution for the complexes LnPhen(TTA)3 (Ln = Eu, Sm, Nd, Yb; Phen = 1,10-phenanthroline; TTA = thenoyltrifluoroacetonate). Thermally excited back-transfer to a charge transfer state was found to occur for Ln = Eu and can be explained by lifetime and intensity back-transfer models. The emission intensity and lifetime were also quenched with increasing temperature for Ln = Sm, and the activation energy for nonradiative decay is similar to that for the thermal population of Sm3+ excited states. Unusual behavior for lifetime and intensity was found for both Ln = Nd, Yb. The usually assumed equivalence of τ/τ0 = I/I0 (where τ is lifetime and I is intensity) does not hold for these cases. We infer that for these lanthanide systems the intensity decreases with temperature in the stage prior to population of the luminescent state. The lifetime changes are discussed.

Superconductivity above 200 K discovered in superhydrides of calcium

Searching for superconductivity with Tc near room temperature is of great interest both for fundamental science & many potential applications. Here we report the experimental discovery of superconductivity with maximum critical temperature (Tc) above 210 K in calcium superhydrides, the new alkali earth hydrides experimentally showing superconductivity above 200 K in addition to sulfur hydride & rare-earth hydride system. The materials are synthesized at the synergetic conditions of 160~190 GPa and ~2000 K using diamond anvil cell combined with in-situ laser heating technique. The superconductivity was studied through in-situ high pressure electric conductance measurements in an applied magnetic field for the sample quenched from high temperature while maintained at high pressures. The upper critical field Hc(0) was estimated to be ~268 T while the GL coherent length is ~11 Å. The in-situ synchrotron X-ray diffraction measurements suggest that the synthesized calcium hydrides are primarily composed of CaH6 while there may also exist other calcium hydrides with different hydrogen contents.

A new finding and technology for selective separation of different REEs from CaO-SiO2-CaF2-P2O5-Fe3O4-RE2O3 system

The significant increase in global consumption of rare earth elements (REEs) has attracted more attention to the separation of REEs from complex rare-earth systems. Bayan Obo ore is the world’s largest rare-earth deposit, where REEs are mainly transfered to RE-concentrate which contains various species of REEs (mainly includes lanthanide: Ce, La, Pr, and Nd). This study reported a new finding and technology for selective separation of different REEs from Bayan Obo RE-concentrate system. The basic data on phase transformation of different REEs in CaO-SiO2-CaF2-P2O5-Fe3O4-RE2O3 systems were reported, and firstly found that different REEs of Ce, La, Pr and Nd could be selectively enriched into cerium oxide, lanthanum ferrate, praseodymium apatite and neodymium apatite, respectively. A novel technology of separating RE-phases via super gravity was proposed, various high-purity RE-phases containing different REEs were separated and characterized, and the crystal information missing in the current database were supplemented.

Square and rhombic lattices of magnetic skyrmions in a centrosymmetric binary compound

Magnetic skyrmions are topologically stable swirling spin textures with particle-like character, and have been intensively studied as a candidate of high-density information bit. While magnetic skyrmions were originally discovered in noncentrosymmetric systems with Dzyaloshinskii-Moriya interaction, recently a nanometric skyrmion lattice has also been reported for centrosymmetric rare-earth compounds, such as Gd2PdSi3 and GdRu2Si2. For the latter systems, a distinct skyrmion formation mechanism mediated by itinerant electrons has been proposed, and the search of a simpler model system allowing for a better understanding of their intricate magnetic phase diagram is highly demanded. Here, we report the discovery of square and rhombic lattices of nanometric skyrmions in a centrosymmetric binary compound EuAl4, by performing small-angle neutron and resonant elastic X-ray scattering experiments. Unlike previously reported centrosymmetric skyrmion-hosting materials, EuAl4 shows multiple-step reorientation of the fundamental magnetic modulation vector as a function of magnetic field, probably reflecting a delicate balance of associated itinerant-electron-mediated interactions. The present results demonstrate that a variety of distinctive skyrmion orders can be derived even in a simple centrosymmetric binary compound, which highlights rare-earth intermetallic systems as a promising platform to realize/control the competition of multiple topological magnetic phases in a single material.