Rare Earth Atoms Research Articles

Structural and electronic properties of Ln2Si6q: (Sm, Eu, Yb; q = 0, −1) clusters

A systematic study on Ln2Si6q (Ln = Sm, Eu, Yb; q = 0, −1) clusters has been performed by density functional theory (DFT). Global minimum searches reveal that the two lanthanide atoms prefer to absorb on the surface of parent silicon-based clusters. Natural population analysis (NPA) is utilized to investigate the electronic and magnetic properties of Ln2Si6q, the electrons always transfer from the lanthanide atoms to parent silicon atoms. Most interestingly, the DFT calculations demonstrate that the magnetic moments of the doped rare earth atoms remain largely localized (13μB for Sm2Si6−/ Eu2Si6−, 12μB for Sm2Si6 and 14μB for Eu2Si6), and the atomic-like magnetism is maintained in the doped cluster. Combined with average binding energy, dissociation energy and HOMO-LUMO gap, Sm2Si6 is probed to the most stable cluster. The current work shows that lanthanide diatom doped silicon-based clusters could have potential utility in new rare earth nanomaterials with tunable magnetic properties.

Pseudo-Relativistic Hartree–Fock and Fully Relativistic Dirac–Hartree–Fock Calculations of Radiative Parameters in the Fifth Spectrum of Lutetium (Lu V)

Using two independent theoretical methods based on the pseudo-relativistic Hartree–Fock (HFR) and the fully relativistic Multiconfigurational Dirac–Hartree–Fock (MCDHF) approaches, we computed the radiative parameters (transition probabilities and oscillator strengths) corresponding to the spectrum of quadruply ionized lutetium (Lu V). The agreement observed between both sets of results allowed us to deduce the radiative rates for a large amount of transitions in order to calculate the contribution of this ion to the opacity of kilonovae in their early phases, i.e., for T = 25,000 K. The results obtained were compared to previous data computed for other quadruply ionized lanthanide atoms, namely La V, Ce V, Pr V, Nd V and Pm V, in order to highlight the main contributors to the opacity among these ions under kilonovae conditions where the Vth spectra are predominant.

Band structure engineering in Fe–Sb based lanthanide filled p-type skutterudites RFe4Sb12 (R = Nd, Sm) to enhance the Seebeck coefficient and thermoelectric figure of merit

Structural, thermodynamic, electronic, and thermoelectric properties of two pure ternary skutterudites, NdFe4Sb12 and SmFe4Sb12, and their doped counterparts, Sm-doped NdFe4Sb12 and Nd-doped SmFe4Sb12, have been investigated using full potential linearized augmented plane wave formalism under density functional theory. In doped systems, the central lanthanide atom was replaced by a different filler atom. Thermodynamic parameters indicate that all the materials are stable, sufficiently hard, and will have a high melting point. Band profiles reveal their semimetallic nature with a pseudo-bandgap above the Fermi level and crossing of the Fermi level of one or more bands. The facts that the trivalent fillers do not provide enough electrons required for charge compensation of Fe4Sb12 and the Fermi levels are well inside the valence band also predict their p-type nature. The splitting of DOS of the f-electrons of the filler atoms into both spin channels implies their ferromagnetic nature. The Sm-doped system exhibits the highest magnetic moment because of the much lower anti-ferromagnetic moment of Fe. Between the pure compounds, the lighter filler atom-based NdFe4Sb12 exhibits a higher ZT value because of the higher population density of states and higher concentration of degenerate flatbands. Contrary to recent predictions, both the doped systems show higher ZT than the pure ones. However, the presence of larger pseudo-bandgaps in both spin channels and two peaks just above the Fermi level in the majority spin channel in the lighter Nd-doped system results in the enhanced Seebeck coefficient, reduced thermal conductivity, and the maximum ZT value of 0.90 at 1000 K.

Shubnikov–de Haas oscillations and nontrivial topological states in Weyl semimetal candidate SmAlSi

The RAlX (R = Light rare earth; X = Ge, Si) compounds, as a family of magnetic Weyl semimetal, have recently attracted growing attention due to the tunability of Weyl nodes and its interactions with diverse magnetism by rare-earth atoms. Here, we report the magnetotransport evidence and electronic structure calculations on nontrivial band topology of SmAlSi, a new member of this family. At low temperatures, SmAlSi exhibits large non-saturated magnetoresistance (MR) (as large as ∼5500% at 2 K and 48 T) and distinct Shubnikov–de Haas (SdH) oscillations. The field dependent MRs at 2 K deviate from the semiclassical (μ 0 H)2 variation but follow the power-law relation MR (μ 0 H) m with a crossover from m ∼ 1.52 at low fields (μ 0 H< 15 T) to m ∼ 1 under high fields (μ 0 H> 18 T), which is attributed to the existence of Weyl points and electron–hole compensated characteristics with high mobility. From the analysis of SdH oscillations, two fundamental frequencies originating from the Fermi surface pockets with non-trivial π Berry phases and small cyclotron mass can be identified, this feature is supported by the calculated electronic band structures with two Weyl pockets near the Fermi level. Our study establishes SmAlSi as a paradigm for researching the novel topological states of RAlX family.

Exploring s-d, s-f, and d-f Electron Interactions in AgnCe+ and AgnSm+ by Chemical Reaction toward O2.

We investigate gas-phase reactions of free AgnCe+ and AgnSm+ clusters with oxygen molecules to explore s-d, s-f, and d-f electron interactions in the finite size regime; a Ce atom has a 5d electron as well as a 4f electron, whereas a Sm atom has six 4f electrons without 5d electrons. In the reaction of AgnCe+ (n = 3-20), the Ce atom located on the cluster surface provides an active site except for n = 15 and 16, as inferred from the composition of the reaction products with oxygen bound to the Ce atom as well as from their relatively high reactivity. The extremely low reactivity for n = 15 and 16 is due to encapsulation of the Ce atom by Ag atoms. The minimum reactivity observed at n = 16 suggests that a closed electronic shell with 18 valence electrons is formed with a delocalized Ce 5d electron, while the localized Ce 4f electron does not contribute to the shell closure. As for AgnSm+ (n = 1-18), encapsulation of the Sm atom was observed for n ≥ 15. The lower reactivity at n = 17 than at n = 16 and 18 implies that an 18-valence-electron shell closure is formed with s electrons from Ag and Sm atoms; Sm 4f electrons are not involved in the shell closure as in the case of AgnCe+. The present results suggest that the 4f electrons tend to localize on the lanthanoid atom, whereas the 5d electron delocalizes to contribute to the electron shell closure.

Rare earth metal element doped g-GaN monolayer : Study of structural, electronic, magnetic, and optical properties by first-principle calculations

Using first-principle calculations, we have studied the structural, electronic, magnetic, and optical properties of the g-GaN monolayer doped with rare earth (RE) metal elements, where RE = La, Ce, Nd, Eu, Gd, and Dy. The substitution of Ga atom with RE leads to the structural deformation in g-GaN monolayer. The RE atom protrudes out from the plane of GaN monolayer. The La@GaN shows non-magnetic behavior similar to g-GaN. The induced magnetism of 1, 3, 6, 7, and 5 μB is observed with Ce, Nd, Eu, Gd, and Dy doped GaN monolayer, respectively. The band gap of g-GaN is 1.98 eV with indirect characteristics. The indirect band gap characteristics of g-GaN retains with La, Gd and Dy doping, while Nd@GaN shows direct band gap behavior. With Ce and Eu doping in GaN monolayer, transformation of semiconducting nature of g-GaN turns to metallic one. The decrease in the work function is observed with the RE doping in GaN monolayer reflects enhanced conductivity. For La, Nd, Gd, and Dy@GaN, the absorption spectrum show similar nature to that of g-GaN spectra. The addition of band edge states near the Fermi of g-GaN show significant red shift in absorption spectrum for Ce and Eu doped GaN monolayers as compared with g-GaN. The absorption spectra of g-GaN extended from UV to IR with the doping of Ce and Eu atom. The static dielectric constant and refractive index of g-GaN monolayer is 1.61 and 1.57, respectively. Overall enhancement in the dielectric constants and refractive indices is seen with RE doping in GaN monolayer as compared to that of g-GaN. This study provides the basis for the development of g-GaN monolayer based optoelectronic devices.

Ln@C60 endohedral fullerenes: A DFT analysis for the complete series from lanthanum to lutetium

We report on a computational study of the complete series of lanthanide atoms encapsulated in C60 fullerene molecule (Ln@C60) by using density functional theory with the PBE functional complemented with the Grimme’s dispersion correction (PBE-D). The goal of the present survey is to account for the influence of step-by-step adding 4f-electrons in lanthanides on the geometrical and electronic properties of Ln@C60 endohedral species. In order to compare the results obtained, we tested two double-numerical basis sets: DN and DND, which are equivalent to the 6-31G and 6-31G(d) Pople-type basis sets. The electronic parameters analyzed comprised the HOMO, LUMO and HOMO-LUMO gap energies, as well as the charge and spin of the encapsulated metal atom. The La and Lu atoms exhibit no tangible spin contribution, whereas in the remaining Ln@C60 species unpaired electrons are found on both lanthanide atom and C60 cage. An intermediate case is the Yb@C60 complex, where only a minor presence of unpaired electrons on the central metal was found.

Magnesium-rich intermetallic compounds RE 3Ag4Mg12 (RE = Y, La–Nd, Sm–Dy, Yb) and AE 3Ag4Mg12 (AE = Ca, Sr)

Abstract The magnesium-rich intermetallic compounds RE 3Ag4Mg12 (RE = Y, La–Nd, Sm–Dy, Yb) and AE 3Ag4Mg12 (AE = Ca, Sr) were synthesized from the elements in sealed tantalum ampoules through heat treatment in an induction furnace. X-ray powder diffraction studies confirm the hexagonal Gd3Ru4Al12 type structure, space group P63/mmc. Three structures were refined from single crystal X-ray diffractometer data: a = 973.47(5), c = 1037.19(5) pm, wR2 = 0.0296, 660 F 2 values, 30 variables for Gd3Ag3.82(1)Mg12.18(1), a = 985.27(9), c = 1047.34(9) pm, wR2 = 0.0367, 716 F 2 values, 29 variables for Yb3Ag3.73(1)Mg12.27(1) and a = 992.41(8), c = 1050.41(8) pm, wR2 = 0.0373, 347 F 2 values, 28 variables for Ca3Ag3.63(1)Mg12.37(1). Refinements of the occupancy parameters revealed substantial Ag/Mg mixing within the silver-magnesium substructure, a consequence of the Ag@Mg8 coordination. The alkaline earth and rare earth atoms build Kagome networks. Temperature dependent magnetic susceptibility measurements indicate diamagnetism/Pauli paramagnetism for the compounds with Ca, Sr, Y and YbII, while the others with the trivalent rare earth elements are Curie-Weiss paramagnets. Most compounds order antiferromagnetically at T N = 4.4(1) K (RE = Pr), 34.6(1) K (RE = Gd) and 23.5(1) K (RE = Tb) while Eu3Ag4Mg12 is a ferromagnet (T C = 19.1(1) K). 151Eu Mössbauer spectra confirm divalent europium (δ = −9.88(1) mm s−1). Full magnetic hyperfine field splitting (18.4(1) T) is observed at 6 K. Yb3Ag4Mg12 shows a single resonance in its 171Yb solid state NMR spectrum at 6991 ppm at 300 K indicating a strong, positive Knight shift.

Chemical interactions of solute atoms during L12 cluster formation in Mg–Zn–Gd alloys with long-period stacking ordered structure

Magnesium-based alloys containing transition metal (TM) and rare-earth (RE) atoms form L12-type TM6RE8 clusters, which are regularly arranged into long-period stacking ordered (LPSO) structures. X-ray absorption spectroscopy (XAS) and ab initio calculations were performed on the solution-treated Mg97Zn1Gd2 alloy before and after aging at 673 K to understand the L12 cluster formation mechanism and the interactions between the TM and RE atoms. Ab initio simulations of Zn K X-ray absorption near edge structure (XANES) spectra showed that the sharpness of the white line depended on the number of Gd atoms. The fine spectral structure changed with the local structure around the Zn atom. The measured XANES spectrum indicated that the Zn in the solution-treated Mg97Zn1Gd2 alloy was initially dissolved in Mg3Gd and then incorporated within L12 clusters after aging. Furthermore, an analysis of the l-projected density of states showed that the sharp white line peak in the XANES spectrum resulted from the interaction of Zn p and Gd f states, which occurred with spinodal decomposition and structural relaxation of L12 clusters. This spinodal decomposition and structural relaxation, caused by the electronic interaction between the RE and TM atoms, may be one of the reasons why rare-earth elements are indispensable for forming an LPSO structure.

Intermetallic compounds RE 2Ga2Mg (RE = Tb–Tm, Lu) with Mo2B2Fe-type structure

Abstract The rare earth intermetallic compounds RE 2Ga2Mg with RE = Tb–Tm and Lu were synthesized from the elements in sealed tantalum ampoules in a high-frequency furnace. These rare earth-rich phases crystallize with the tetragonal Mo2B2Fe-type structure, space group P4/mbm and Z = 2. The polycrystalline samples were characterized through their Guinier powder patterns. The structures of Er2Ga2.092(1)Mg0.908(1), Tm2Ga2.037(1)Mg0.963(1) and Lu2Ga2.176(1)Mg0.824(1) have been refined from single crystal X-ray diffractometer data. The refinements revealed small homogeneity ranges (small degrees of Mg/Ga mixing on the 2a sites). The magnesium atoms show square planar coordination by Ga2 dumbbells (282 pm Mg–Ga and 257 pm Ga–Ga in the lutetium compound). Geometrically one can describe the RE 2Ga2Mg phases as 1:1 intergrowth structures of CsCl and AlB2-related slabs of compositions REMg and REGa2. From DFT based calculations, charge transfer from the rare earth and magnesium atoms towards gallium can be illustrated in electron localization function ELF slice planes showing strong localization around gallium in the basal plane as well as along the tetragonal c axis signaling Ga–Ga pair interactions. The site-projected density of states DOS and COOP data further quantify this observation. Temperature dependent magnetic susceptibility measurements show Pauli paramagnetism for Sc2Ga2Mg and Lu2Ga2Mg with low room temperature susceptibility values of 2.1(1) × 10−4 and 1.1(1) × 10−4 emu mol−1, respectively. Ho2Ga2Mg, Er2Ga2Mg and Tm2Ga2Mg are Curie-Weiss paramagnets with stable trivalent rare earth ground states. Antiferromagnetic ordering was detected below the Néel temperatures of T N = 18.6(1) (RE = Ho), 11.9(1) (RE = Er) and 6.4(1) K (RE = Tm). The three compounds show metamagnetic transitions in their 3 K magnetization isotherms. Tm2Ga2Mg exhibits a square loop behavior with small hysteresis.

Thermal conductivity of an ultracold paramagnetic Bose gas

We analytically derive the transport tensor of thermal conductivity in an ultracold, but not yet quantum degenerate, gas of Bosonic lanthanide atoms using the Chapman-Enskog procedure. The tensor coefficients inherit an anisotropy from the anisotropic collision cross section for these dipolar species, manifest in their dependence on the dipole moment, dipole orientation, and $s$-wave scattering length. These functional dependences open up a pathway for control of macroscopic gas phenomena via tuning of the microscopic atomic interactions. As an illustrative example, we analyze the time evolution of a temperature hot spot which shows preferential heat diffusion orthogonal to the dipole orientation, a direct consequence of anisotropic thermal conduction.

Preparation of pyrrolidinyl diglycolamide bonded silica particles and its rare earth separation properties

The separation of rare earth elements by solid phase containing diglycolamide-type ligands is a hot topic. In this study, 2-[2-oxo-2-(1-pyrrolidinyl)ethoxy]acetic acid (PYRDGA) was synthesized and attached to the silica. The binding strength of SiO2@PYRDGA for rare earths showed a single increasing trend with the radius of rare earth atoms. IR and XPS spectra demonstrated that carbonyl oxygen and ether bond oxygen are binding sites for rare earth ions. SiO2@PYRDGA was used for the chromatographic separation of REEs, and the primary separation of 16 REEs was achieved at pH = 2.0 using HNO3 solution as the eluent, and La, Ce, Pr, Nd, Sm, and Eu reached the baseline separation level.

THEORETICAL STUDYING SPECTRAL CHARACTERISTICS OF Tm ATOM WITHIN OPTIMIZED RELATIVISTIC MANY-BODY THEORY

Theoretical studying Rydberg spectrum of complex lanthanide atom of Tm has been performed within the relativistic many-body perturbation theory and generalized relativistic energy approach. The zeroth approximation of the relativistic perturbation theory is provided by the optimized Dirac-Kohn-Sham-Breit ones. Optimization has been fulfilled by means of introduction of the special gauge parameter to the Fock and Kohn-Sham exchange potentials and further minimization of the gauge-non-invariant contributions into radiation width of atomic levels with using relativistic orbital sets, generated by the corresponding zeroth approximation Hamiltonian. The calculated energies and widths of autoionization resonant states 4f--1j 6s(J12)nsnp[J] of the Tm atom with n=25-35 are presented and compared with known theoretical results, received within other approaches. Two main types of the Rydberg autoionization resonances decay, namely, the classic Beutler-Fano decay channel and a new Ivanov et al reorientation-type decay channel ar4e studied. It is noted that, for example, for autoionization resonant states with the considered values of n, the decay of resonances occurs along both channels, and it is extremely difficult to understand a priori which of them is dominant.

Anisotropic magnetic property of single crystals RV6Sn6 (R=Y, Gd−Tm, Lu)

$R$V${_6}$Sn${_6}$ ($R$ = Y, Gd - Tm, Lu) single crystals are synthesized by Sn-flux method and their physical properties are characterized by magnetization, resistivity, and specific heat measurements. Powder X-ray diffraction patterns of all samples can be well indexed with the hexagonal HfFe$_6$Ge$_6$-type structure, where rare-earth atoms form hexagonal layers and vanadium atoms form Kagome layers. At high temperatures, magnetic susceptibility measurements of moment bearing rare-earths ($R$ = Gd - Tm) follow Curie-Weiss behavior. Effective moments estimated from the polycrystalline average of magnetic susceptibility curves are consistent with the values for free $R^{3+}$ ion. Strong magnetic anisotropy due to crystalline electric field effects is observed for moment bearing rare-earths, except GdV$_6$Sn$_6$. The easy magnetization direction is determined to be $c$-axis for $R$ = Tb - Ho and $ab$-plane for $R$ = Er, and Tm. The vanadium ions in $R$V${_6}$Sn${_6}$ possess no magnetic moment. The compounds for $R$ = Y and Lu exhibit typical characteristics of paramagnetic metals. At low temperatures, the magnetic ordering is confirmed from magnetization, specific heat, and resistivity: the highest $T_{N} = 4.9$~K for GdV$_6$Sn$_6$ and the lowest $T_{N} = 2.3$~K for HoV$_6$Sn$_6$. No magnetic ordering is observed down to 1.8~K for $R$ = Er and Tm. A slight deviation of the magnetic ordering temperature from the de Gennes scaling suggests the dominant Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction between rare-earth moments in metallic $R$V${_6}$Sn${_6}$ compounds.

Formation and fragmentation of quantum droplets in a quasi-one-dimensional dipolar Bose gas

We theoretically investigate the droplets formation in a tightly trapped one-dimensional dipolar gas of bosonic atoms. When the strength of the dipolar interaction becomes sufficiently attractive compared to the contact one, we show how a solitoniclike density profile evolves into a liquidlike droplet on increasing the number of particles in the trap. The incipient gas-liquid transition is also signaled by a steep increase of the breathing mode and a change in sign of the chemical potential. Upon a sudden release of the trap, varying the number of trapped atoms and the scattering length, the numerical solution of a time-dependent generalized Gross-Pitaevskii equation shows either an evaporation of the cloud, the formation of a single self-bound droplet, or a fragmentation in multiple droplets. These results can be probed with lanthanide atoms and help in characterizing the effect of the dipolar interaction in a quasi-one-dimensional geometry.

Optical and Structural Characteristics of Rare Earth-Doped ZnO Nanocrystals Prepared in Colloidal Solution

ZnO nanocrystals doped with Nd, Gd, and Er were synthesized using a soft chemical process in ambient atmosphere. Pseudospherical and hexagonal nanocrystals (NC) of the wurtzite phase with a mean size of (7.4 ± 1.7) nm were obtained. The presence of rare earth (RE) dopants was confirmed by X-ray fluorescence (XRF) spectroscopy. The ZnO nanocrystals exhibited simultaneously narrow excitonic- and broad trap/surface-related photoluminescence (PL), both of which were affected by doping with RE atoms. Doping reduced the total PL intensity, suppressing the excitonic emission by a greater extent than the broad band PL. Also, doping resulted in a blue shift of the trap/surface-related emission, while the energy of the excitonic peak remained unchanged. Resonant Raman spectra additionally confirmed the wurtzite phase of ZnO NCs and revealed a shift of the A1-LO mode towards lower frequency upon doping that could be caused by the mass effect of RE atoms, point defects, and increases in charge carrier concentration. Fitting of the spectra with Voigt profiles showed better results with two surface optical (SO) phonon modes that were previously theoretically predicted for the wurtzite ZnO phase. The influence of RE doping on PL and Raman spectra can be explained by the incorporation of RE ions into the ZnO nanostructures, where the dopants act as non-radiative defects.

Electronic properties and defect levels induced by [formula omitted]-type defect-complexes in Ge

Defect-complexes are point defects that significantly influence the geometric, optical, and electrical properties of materials. Defect-complexes are known to improve the electronic and electrical properties of Ge. Deep and shallow defect levels in Ge have been linked to defect-complexes formed by the double self-interstitials and rare earth atoms. Despite this breakthrough, several defect-complexes in Ge are not well understood; hence may pose as a challenge to the optimal performance of Ge based devices. In this study, we present the results of the hybrid density functional theory calculations of substitutional and interstitial defect-complexes (BGeNi, NGeBi, AlGePi, PGeAli, GaGeAsi, AsGeGai, InGeSbi, and SbGeIni) in Ge. Their formation energies, electronic properties, defect-complex stability and induced defect levels in Ge were predicted. While the formation energies of the defect-complexes formed by the P and Al atoms were relatively low and energetically more favourable, those defect-complexes formed by the B and N atoms were the least energetically favourable. Except for the BGeNi, all the defect-complexes significantly bound with energies lower than their formation energies. The NGeBi and PGeAli essential donor levels were in the band gap of Ge. A shallow double acceptor defect level was found to be associated with the AlGePi, while the InGeSbi induced a shallow double donor defect level. The electrical inactive defect-complexes were the BGeNi, GaGeAsi, AsGeGai and SbGeIni. The results of this report are important, as they provide theoretical insight of the prediction of the n/p-type substitutional and interstitial defect-complexes in Ge.

Hyperion: A New Computational Tool for Relativistic Ab Initio Hyperfine Coupling.

Herein we describe Hyperion, a new program for computing relativistic picture-change-corrected magnetic resonance parameters from scalar relativistic active space wave functions, with or without spin–orbit coupling (SOC) included a posteriori. Hyperion also includes a new orbital decomposition method for assisting active space selection for calculations of hyperfine coupling. For benchmarking purposes, we determine hyperfine coupling constants of selected alkali metal, transition metal, and lanthanide atoms, based on complete active space self-consistent field spin–orbit calculations in OpenMolcas. Our results are in excellent agreement with experimental data from atomic spectroscopy as well as theoretical predictions from four-component relativistic calculations.

Magneto-optic Kerr effect in Gd20Co80 alloy

The magneto-optical Kerr effect in Gd20Co80 alloy and cobalt thin films has been studied in a broad spectral range applying spectral ellipsometry experimental technique. The results of the experiments showed the complex nature of the complex Kerr angle dispersion curves. A quantum mechanical formalism for degenerate and non-degenerate Landau levels for quasi-free electrons in ferromagnetic material has been developed in order to analyze the experimental data. The equivalence of relations for off-diagonal dielectric tensor elements for non-degenerate Landau levels to the classical case of the motion of quasi-free electrons along circular trajectories in a magnetic field has been theoretically shown. The degenerate Landau levels in this approach are the result of motion of electrons in small confined volumes near rare-earth alloy atoms. Rotation of light polarization occurs in this case due to transitions between subbands having different magnetic quantum numbers. This theoretical approach allowed us to interpret in detail shapes and sign of the complex Kerr angle dispersion curves, which actually include the contributions of optical transitions between degenerate and non-degenerate energy levels. The complex Kerr angle sign is determined by the magnetization magnetic field direction for non-degenerate Landau levels and the Hund rule for degenerate Landau levels.

Slow Magnetic Relaxation of Dy Adatoms with In-Plane Magnetic Anisotropy on a Two-Dimensional Electron Gas.

We report on the magnetic properties of Dy atoms adsorbed on the (001) surface of SrTiO3. X-ray magnetic circular dichroism reveals slow relaxation of the Dy magnetization on a time scale of about 800 s at 2.5 K, unusually associated with an easy-plane magnetic anisotropy. We attribute these properties to Dy atoms occupying hollow adsorption sites on the TiO2-terminated surface. Conversely, Ho atoms adsorbed on the same surface show paramagnetic behavior down to 2.5 K. With the help of atomic multiplet simulations and first-principles calculations, we establish that Dy populates also the top-O and bridge sites on the coexisting SrO-terminated surface. A simple magnetization relaxation model predicts these two sites to have an even longer magnetization lifetime than the hollow site. Moreover, the adsorption of Dy on the insulating SrTiO3 crystal leads, regardless of the surface termination, to the formation of a spin-polarized two-dimensional electron gas of Ti 3dxy character, together with an antiferromagnetic Dy–Ti coupling. Our findings support the feasibility of tuning the magnetic properties of the rare-earth atoms by acting on the substrate electronic gas with electric fields.