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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Spontaneous emission dynamics of Eu 3+ ions coupled to hyperbolic metamaterials

We show that sub-wavelength nanostructured systems with tunable electromagnetic properties, such as hyperbolic metamaterials (HMMs), provide a useful platform to tailor spontaneous emission processes. Here, we investigate a system comprising Eu 3+ (NO 3 ) 3 ·6H 2 O nanocrystals on an HMM structure featuring a hexagonal array of Ag nanowires in a porous Al2O 3 matrix. The HMM-coupled Eu 3+ ions exhibit up to a 2.4 fold increase in their decay rate, accompanied by an enhancement of the emission rate of the 5 D 0 → 7 F 2 transition. Using finite-difference time-domain modeling, we corroborate these observations with the increase in the photonic density of states seen by the Eu 3+ ions in the proximity of the HMM. Our results indicate that HMMs can serve as a valuable tool to control the emission from weak transitions and, hence, hint at a route toward more practical applications of rare-earth ions in nanoscale optoelectronics and quantum devices.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Magnetic field induced modification of a first-order ferromagnetic transition in Eu 2 ⁢In

Here, we present a comprehensive study of the temperature-and magnetic-field-dependent magnetization, specific heat, and local crystal structure across the first-order ferromagnetic–paramagnetic transition in Eu 2 ⁢In. Anomalies in the magnetocaloric response are observed near 𝐻 ≈ 25 kOe, including changes in field scaling of magnetic entropy, local entropy exponent, and universal master curve, which suggest an apparent weakening of the first-order character of the transition. However, quantitative analysis of the magnetocaloric parameters together with modified Arrott plots demonstrates that the transition remains first order up to at least 70 kOe. Specific-heat measurements reveal a field-induced splitting of the sharp zero-field anomaly into a doublet, providing a natural explanation for the change in the magnetocaloric response. Magnetic-field-dependent extended x-ray absorption fine structure (EXAFS) measurements show no detectable field-induced changes in the local coordination environment of Eu. We therefore attribute these observations to a magnetic-field-induced two-step transition process in Eu 2 ⁢In.

Kumar, Ajay [Ames Laboratory (AMES), Ames, IA (Uni↗
DOE OSTI2022

Magnetic field induced a b -plane rotation of the Eu magnetic moments in trigonal EuMg 2 Bi 2 and EuMg 2 Sb 2 single crystals below their Néel temperatures

The thermodynamic and electronic-transport properties of trigonal EuMg 2 Bi 2 in ab-plane magnetic fields H x and the A-type antiferromagnetic structure have recently been reported. The Eu magnetic moments with spin S = 7/2 remain locked in the ab plane up to and above the ab-plane critical field $H^{c}_{x}$ = 27.5 kOe at which the Eu moments become parallel to H x . Here additional measurements at low fields are reported that reveal a new spin-reorientation transition at a field H c1 ≈ 465 Oe where the Eu moments remain in the ab plane but become perpendicular to H x . At higher fields, the moments cant toward the field resulting in M ∝ H x up to $H^{c}_{x}$. Similar results are reported from measurements of the magnetic properties of EuMg 2 Sb 2 single crystals, where H c1 ≈ 220 Oe is found. Theory is formulated that models the low-field magnetic behavior of both materials, and the associated anisotropies are calculated. Further, the ab-plane trigonal anisotropy in EuMg 2 Sb 2 is found to be significantly smaller than in EuMg 2 Bi 2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Magnetism in the axion insulator candidate Eu 5 In 2 Sb 6

Eu 5 In 2 Sb 6 is a member of a family of orthorhombic nonsymmorphic rare-earth intermetallics that combines large localized magnetic moments and itinerant exchange with a low carrier density and perpendicular glide planes. This may result in special topological crystalline (wallpaper fermion) or axion insulating phases. Recent studies of Eu 5 In 2 Sb 6 single crystals have revealed colossal negative magnetoresistance and multiple magnetic phase transitions. Here, we clarify this ordering process using neutron scattering, resonant elastic x-ray scattering, muon spin-rotation, and magnetometry. The nonsymmorphic and multisite character of Eu 5 In 2 Sb 6 results in coplanar noncollinear magnetic structures with an Ising-like net magnetization along the a axis. A reordering transition, attributable to competing ferro- and antiferromagnetic couplings, manifests as the onset of a second commensurate Fourier component. In the absence of spatially resolved probes, the experimental evidence for this low-temperature state can be interpreted either as an unusual double- q structure or in a phase separation scenario. The net magnetization produces variable anisotropic hysteretic effects which also couple to charge transport. The implied potential for functional domain physics and topological transport suggests that this structural family may be a promising platform to implement concepts of topological antiferromagnetic spintronics. Published by the American Physical Society 2024

Rahn, M. C. (ORCID:0000000174038288)↗
DOE OSTI2024

Europium c -axis ferromagnetism in Eu ( Co 1 - x Ni x ) 2 - y As 2 : A single-crystal neutron diffraction study

Here we report neutron diffraction results for the body-centered-tetragonal series Eu⁢(Co 1-x ⁢Ni x ) 2-y As 2 , x=0.10, 0.20, 0.42, and 0.82, y≤0.10, that detail changes to the magnetic ordering with nominal hole doping. We report the antiferromagnetic (AFM) propagation vectors, magnetic transition temperatures, and the ordered magnetic moments. We find a nonmonotonic change of the AFM propagation vector with x, with a minimum occurring at the tetragonal to collapsed-tetragonal phase crossover. For x=0.10 and 0.82 we find c-axis helix ordering of the Eu magnetic moments (spins) similar to x=0 and 1, with the spins oriented within the ab-plane. For x=0.20 and 0.42 we find higher-temperature c-axis ferromagnetic (FM) order and lower-temperature c-axis cone order. Using the extinction conditions for the space group, we discovered that the Eu spins are ordered in the higher-temperature c-axis FM phase for intermediate values of x, contrary to a previous report suggesting only Co/Ni spin ordering. Although we cannot directly confirm that the Co/Ni spins are also ordered, we suggest that c-axis itinerant-FM ordering of the Co/Ni spins could provide a molecular field that drives FM ordering of the Eu spins, which in turn provides the anisotropy for the lower-temperature c-axis cone order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Crystal growth and magnetic structure of ternary silicide Eu Pd 3 Si 2

The hexagonal CaCu 5 –type structure (P6/mmm) is the prototype for more than 100 ternary borides, gallides, and silicides, with general stoichiometry of RTM 3 X 2 (R=lanthanide/alkaline earth; TM=transition metal; X=B, Ga, Si, Ge). Here we report the synthesis, crystal structure, and bulk magnetic properties of polycrystalline and single crystal samples of EuPd 3 Si 2 and its nonmagnetic analog SrPd 3 Si 2 . Both compounds crystallize in the orthorhombic space group symmetry Imma (no. 74, Z = 2, oI12) displaying pseudohexagonal symmetry. Ferromagnetic (FM) order of Eu 2+ at T C1 =78K and a spin-reorientation transition at T C2 =5K appear as distinctive features in bulk magnetization, specific heat, and resistivity/resistance measurements. Neutron powder diffraction measurements on EuPd 3 Si 2 confirm FM order of the Eu 2+ spins below T C1 , with the spins aligned along the a axis below T C2 . Electronic band structure calculations corroborate the crystal structure and the FM state for EuPd 3 Si 2 , with a Pd d–band polarization in the same direction as the Eu 4f polarization, enhancing the observed spin moment.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Physical properties of intergrowth compound Eu 2 CuZn 2 P 3

Here, the physical properties of single-crystalline Eu 2 ⁢CuZn 2 ⁢P 3 were inspected via thermodynamic, transport, and neutron diffraction measurements. Eu 2 ⁢ CuZn 2⁢ P 3 is composed of EuCuP and EuZn 2 ⁢ P 2 motifs stacked in a one-to-one ratio. The magnetic response of Eu 2 ⁢ CuZn 2 ⁢ P 3 is similar to that of EuZn 2 ⁢ P 2 in its A-type antiferromagnetic (semiconducting) state. A Néel temperature of T N = 40.3K is obtained from the specific heat capacity. Single-crystal neutron diffraction reveals a (001) magnetic propagation vector, with primarily in-plane moments coupled along [001] in an up-up-down-down pattern. This spin structure retains the ferromagnetic EuCuP motifs and antiferromagnetic coupling across the EuZn 2 ⁢P 2 motifs. The electrical resistivity is characterized by metallic behavior above 100 K, an increase in ρ upon cooling below ≈ 75K, and a large negative magnetoresistance below T N . First principles calculations evidence a narrow band gap for antiferromagnetic ordering and semimetallic behavior for the ferromagnetic state. This is consistent with the observed effect of magnetic field on the electrical resistivity. Hall effect measurements reveal a field-induced, negative anomalous Hall effect that increases on cooling down to 2 K. Also, an unconventional contribution to the Hall effect dominates the low-field Hall signal, particularly near T N , and is similar in appearance to a topological Hall effect. However, further work is necessary to understand if any of the transport properties have topological origins or if magnetism-induced modifications to the Fermi surface induce these unusual Hall effect signals in this and related materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Unconventional magnetotransport and antiferromagnetic order in Eu 2 ⁢InTe 5

Here, we report on the structural characterization and physical properties of Eu 2 ⁢InTe 5 , a distorted square-net motif antiferromagnetic semiconductor. Single crystal x-ray diffraction measurements reveal a distortion of the Te square-net layers such that an orthorhombic supercell is necessary to accurately describe the structure. Magnetization, resistivity, and specific heat measurements confirm antiferromagnetic ordering at 𝑇 𝑁 = 7.3K. Anisotropy in magnetization data suggests the magnetic moments are oriented parallel to the 𝑐 axis. We observe an unconventional transverse magnetoresistance and Hall resistivity in the paramagnetic state (𝑇 ≤ 80K), indicating strong coupling between localized Eu 2+ magnetic moments and conduction electrons. Resistivity and Hall measurements indicate the material is a heavily doped semiconductor, with impurity states related to disorder. Our findings highlight a relatively unexplored Eu-based antiferromagnetic semiconductor with unconventional magnetotransport behavior.

Cook, Matthew S. [Oak Ridge National Laboratory (O↗
NASA NTRS1989

Is plagioclase removal responsible for the negative Eu anomaly in the source regions of mare basalts?

The nearly ubiquitous presence of a negative Eu anomaly in the mare basalts has been suggested to indicate prior separation and flotation of plagioclase from the basalt source region during its crystallization from a lunar magma ocean (LMO). Are there any mare basalts derived from a mantle source which did not experience prior plagioclase separation? Crystal chemical rationale for REE substitution in pyroxene suggests that the combination of REE size and charge, M2 site characteristics of pyroxene, fO2, magma chemistry, and temperature may account for the negative Eu anomaly in the source region of some types of primitive, low TiO2 mare basalts. This origin for the negative Eu anomaly does not preclude the possibility of the LMO as many mare basalts still require prior plagioclase crystallization and separation and/or hybridization involving a KREEP component.

Shearer, C. K.↗
NASA NTRS2006

Aluminum Effect on the Calibration of the Eu Oxybarometer for Nakhlites

Recent studies of Martian meteorites have shown that Martian magma had wide range of oxygen fugacity. In order to estimate the redox state of the Martian crust and mantle, the partitioning coefficient of Eu in the shergottite pyroxene has been extensively studied. Nakhlite, a cumulate clinopyroxenite, is another important group of Martian meteorites. We have studied synthetic compositions (NT, NL, NJ, NJ2 and NJ4) in order to estimate the Nakhla parent melt composition. In our previous work, we calibrated the Eu oxybarometer for nakhlite using the NJ4 composition which we believe is the closest to the Nakhla parent melt. Consequently, we concluded that Nakhla may have crystallized under fairly reducing condition. However, we also found that the partition coefficient is strongly affected by Al contents in melt and in pyroxene. In this abstract we report the correlation between the D values and Al contents in melt and in pyroxene from our Nakhla experimental studies. Also we check the reliability of our previous calibration of Eu oxybarometer, because Rare Earth Elements (REEs) are easily affected by Al content in melt and in pyroxene and Nakhla pyroxene shows unusual patchy Al zoning.

Makishima, J.↗
DOE OSTI2020

Materials Data on Eu(Cu2As)2 by Materials Project

Eu(Cu2As)2 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Eu2+ is bonded to six equivalent As3- atoms to form edge-sharing EuAs6 octahedra. All Eu–As bond lengths are 3.04 Å. There are two inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded in a distorted trigonal non-coplanar geometry to three equivalent As3- atoms. All Cu–As bond lengths are 2.47 Å. In the second Cu1+ site, Cu1+ is bonded in a distorted single-bond geometry to four equivalent As3- atoms. There are one shorter (2.45 Å) and three longer (2.83 Å) Cu–As bond lengths. As3- is bonded in a 10-coordinate geometry to three equivalent Eu2+ and seven Cu1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(POs)2 by Materials Project

Eu(OsP)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Eu2+ is bonded in a 8-coordinate geometry to eight equivalent Os2- atoms. All Eu–Os bond lengths are 3.38 Å. Os2- is bonded in a 12-coordinate geometry to four equivalent Eu2+ and four equivalent P1+ atoms. All Os–P bond lengths are 2.34 Å. P1+ is bonded in a 4-coordinate geometry to four equivalent Os2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(SiAu)2 by Materials Project

Eu(AuSi)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Eu2+ is bonded in a 8-coordinate geometry to eight equivalent Au1- atoms. All Eu–Au bond lengths are 3.37 Å. Au1- is bonded to four equivalent Eu2+ and four equivalent Si atoms to form a mixture of distorted edge, face, and corner-sharing AuEu4Si4 tetrahedra. All Au–Si bond lengths are 2.59 Å. Si is bonded in a 5-coordinate geometry to four equivalent Au1- and one Si atom. The Si–Si bond length is 2.35 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(Ni5P3)2 by Materials Project

Eu(Ni5P3)2 crystallizes in the orthorhombic Cmce space group. The structure is three-dimensional. Eu2+ is bonded in a 12-coordinate geometry to eight P3- atoms. There are a spread of Eu–P bond distances ranging from 3.19–3.56 Å. There are four inequivalent Ni+1.60+ sites. In the first Ni+1.60+ site, Ni+1.60+ is bonded in a distorted rectangular see-saw-like geometry to four P3- atoms. There are a spread of Ni–P bond distances ranging from 2.32–2.48 Å. In the second Ni+1.60+ site, Ni+1.60+ is bonded to four P3- atoms to form a mixture of distorted edge and corner-sharing NiP4 tetrahedra. There are two shorter (2.24 Å) and two longer (2.34 Å) Ni–P bond lengths. In the third Ni+1.60+ site, Ni+1.60+ is bonded to four P3- atoms to form a mixture of edge and corner-sharing NiP4 tetrahedra. There are a spread of Ni–P bond distances ranging from 2.16–2.29 Å. In the fourth Ni+1.60+ site, Ni+1.60+ is bonded to four P3- atoms to form a mixture of edge and corner-sharing NiP4 tetrahedra. There are a spread of Ni–P bond distances ranging from 2.19–2.33 Å. There are three inequivalent P3- sites. In the first P3- site, P3- is bonded in a 6-coordinate geometry to two equivalent Eu2+ and six Ni+1.60+ atoms. In the second P3- site, P3- is bonded in a 6-coordinate geometry to one Eu2+ and six Ni+1.60+ atoms. In the third P3- site, P3- is bonded in a 8-coordinate geometry to one Eu2+ and eight Ni+1.60+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(BO2)3 by Materials Project

Eu(BO2)3 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Eu3+ is bonded in a 2-coordinate geometry to ten O2- atoms. There are a spread of Eu–O bond distances ranging from 2.38–2.89 Å. There are two inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.46 Å) and two longer (1.49 Å) B–O bond length. In the second B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.34–1.41 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent Eu3+ and two B3+ atoms. In the second O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Eu3+ and one B3+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one Eu3+ and two B3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(PRu)2 by Materials Project

Eu(RuP)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Eu2+ is bonded in a body-centered cubic geometry to eight equivalent P3- atoms. All Eu–P bond lengths are 3.26 Å. Ru2+ is bonded to four equivalent P3- atoms to form a mixture of edge and corner-sharing RuP4 tetrahedra. All Ru–P bond lengths are 2.33 Å. P3- is bonded in a 8-coordinate geometry to four equivalent Eu2+ and four equivalent Ru2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(LuS2)2 by Materials Project

Eu(LuS2)2 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Lu3+ is bonded in a 8-coordinate geometry to eight equivalent S2- atoms. There are a spread of Lu–S bond distances ranging from 2.68–3.10 Å. Eu2+ is bonded in a 8-coordinate geometry to eight equivalent S2- atoms. There are four shorter (2.84 Å) and four longer (3.06 Å) Eu–S bond lengths. S2- is bonded in a 6-coordinate geometry to four equivalent Lu3+ and two equivalent Eu2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(YS2)2 by Materials Project

Eu(YS2)2 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Eu2+ is bonded to eight equivalent S2- atoms to form distorted edge-sharing EuS8 hexagonal bipyramids. There are four shorter (2.87 Å) and four longer (3.07 Å) Eu–S bond lengths. Y3+ is bonded in a 8-coordinate geometry to eight equivalent S2- atoms. There are a spread of Y–S bond distances ranging from 2.75–3.07 Å. S2- is bonded in a 6-coordinate geometry to two equivalent Eu2+ and four equivalent Y3+ atoms.

36 MATERIALS SCIENCE↗