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Rai, Binod K.

Publications and source records attributed to Rai, Binod K..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Nanometric modulations of the magnetic structure of the element Nd

The rare earth neodymium arguably exhibits the most complex magnetic ordering and series of magnetic phase transitions of the elements. Here we report the results of small-angle neutron scattering (SANS) measurements as a function of temperature and applied magnetic field to study magnetic correlations on nanometer length scales in Nd. We support these results with additional neutron diffraction, thermodynamic and synchrotron x-ray measurements. The SANS measurements reveal the presence of modulation vectors characterizing the ordered spin configuration which exhibit changes in magnitude and direction that are phase dependent. Between 5.9 and 7.6 K an additional modulation vector is observed with magnitude Q = 0.12 Å -1 . This scattering appears to originate from order of the Nd layers which contain a center of inversion. Tracking this modulation vector as a function of magnetic field indicates a phase boundary at ≈1 T. The modulation vectors observed in this study establish the presence of nanometer length scale spin textures which are likely stabilized by frustrated Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Magnetic Materials Research at SRNL

Introduction – What are Magnetic Materials? Magnetic materials are crystalline solids which below a certain temperature, known as the ordering temperature, display spontaneous order in their magnetic moments. Results • Enhanced thermal stability and saturation magnetization with Y substitution in Ce2Fe14B based permanent magnets • Discovered a new ferromagnetic phase transition at TC = 62.9 K in (Dy1/3Mo2/3)2AlC and validated the two previously reported low temperature magnetic phases Characterization of Magnetic Materials Raw high purity materials are melted together to synthesize a crystalline sample using an arc melter at Savannah River National Laboratory (SRNL). Use high energy ball milling to form a hard/soft magnetic composite using Y substituted Ce2Fe14B. Finish structural characterization on γ- irradiated (RE1/3Mo2/3)2AlC (RE = Rare Earth) MAX samples. Unit Cell Lattice Points

Bretana, Alex↗
DOE OSTI2024

Synthesis and characterization of properties of (Tb1/3Mo2/3)2AlC polycrystalline

When molecules, atoms, or ions are grouped in a highly ordered microscopic structure to form a crystal lattice that stretches in all directions, the result is a solid material known as a crystal or crystalline solid. They are arranged in a highly ordered microscopic structure to form a crystal lattice. The smallest group of particles in material that constitutes this repeating pattern is unit cell of the structure. The unit cell is a repeating unit formed by the vectors spanning the points of a lattice.

Bretana, Alex↗
DOE OSTI2024

Magnetic Materials Research at SRNL

Fig: Rietveld Refinement of room temperature PXRD data for annealed Ce2Fe14B (left panel), (Y0.1Ce1.9)Fe14B (middle panel), and (Lu0.1Ce1.90)Fe14B (right panel) alloys. All annealed alloys plotted are composed primarily of Ce2Fe14B phase with small α-Fe impurities. Vertical blue ticks correspond to the position of the calculated Bragg peaks of all phases (from top to bottom, 2-14-1 and α-Fe). Fig: (Left Panel) Field dependent magnetization measurements on aligned powder with the magnetic field applied along the easy direction for annealed Ce2Fe14B and (YxCe2-x)Fe14B (x=0.1, 0.2, 0.3, 0.4, 0.5) alloys. (Middle Panel) Field dependent magnetization measurements on aligned powder with the magnetic field applied along the hard direction for annealed Ce2Fe14B and (YxCe2-x)Fe14B (x=0.1, 0.2, 0.3, 0.4, 0.5) alloys. (Right Panel) The saturation magnetization of Ce2Fe14B and (YxCe2-x)Fe14B (x=0.1, 0.2, 0.3, 0.4, 0.5) alloys as determined from easy axis field dependent magnetization measurements.

Bretana, Alex↗
DOE OSTI2024

Crystal structure and magnetism of actinide oxides: a review

In actinide systems, the 5f electrons experience a uniquely delicate balance of effects and interactions having similar energy scales, which are often difficult to properly disentangle. This interplay of factors such as the dual nature of 5f-states, strong electronic correlations, and strong spin–orbit coupling results in electronically unusual and intriguing behavior such as multi-k antiferromagnetic ordering, multipolar ordering, Mott-physics, mixed valence configurations, and more. Despite the inherent allure of their exotic properties, the exploratory science of even the more basic, binary systems like the actinide oxides has been limited due to their toxicity, radioactivity, and reactivity. In this article, we provide an overview of the available synthesis techniques for selected binary actinide oxides, including the actinide dioxides, sesquioxides, and a selection of higher oxides. For these oxides, here we also review and evaluate the current state of knowledge of their crystal structures and magnetic properties. In many aspects, substantial knowledge gaps exist in the current body of research on actinide oxides related to understanding their electronic ground states. Bridging these gaps is vital for improving not only a fundamental understanding of these systems but also of future nuclear technologies. To this end, we note the experimental techniques and necessary future investigations which may aid in better elucidating the nature of these fascinating systems.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Magnetic properties of Lutetium and Yttrium doped Ce 2 Fe 14 B magnets

The increasing demand for Nd-Dy and Sm-Co based permanent magnets is exacerbating the current critical materials shortage, therefore improving and optimizing current candidate critical element free permanent magnets is necessary to develop future clean energy technologies. In this work, we aim to increase the thermal stability and magnetic performance of Ce 2 Fe 14 B based permanent magnets through the substitution of Ce ions with noncritical rare earth elements Lu and Y. The substitution of Lu (x=0; 0.05; 0.1; 0.15) for Ce ions in (LuxCe 2-x )Fe 14 B was unsuccessful, likely due to disparities in ionic size and valencies, and failed to exhibit improved thermal stability or magnetic performance. In contrast, Y substitution for Ce ions in (Y x Ce 2-x )Fe14B (x= 0.1; 0.2; 0.3; 0.4; 0.5) alloys was successful. Notably, these alloys demonstrated enhanced thermal stability, as evidenced by an increase in the Curie temperature, reaching a peak of 443 K at x= 0.5. Y substitution also helped to suppress the CeFe2 Laves phase. Without loss of the anisotropy field Y substitution increased the saturation magnetization, MS, peaking at MS = 125 emu/g for a Y concentration of x= 0:4, demonstrating (Y 0.4 Ce 1.6 )Fe 14 B as a potential critical element free permanent magnet with an energy product as high as 29 MGOe. This work is advantageous in developing low cost high performance permanent magnets with reduced or little to no critical rare earth elements.

Rai, Binod K.↗
DOE OSTI2023

Structure and properties of NdCuGa 3 single crystals

Here this manuscript reports on the structural and magnetic properties of NdCuGa 3 using powder and single crystal X-ray diffraction (XRD), zero-field single crystal neutron diffraction, magnetization, and specific heat measurements. Our XRD on a single crystal specimen of NdCuGa3 confirmed that it crystallizes in the tetragonal BaNiSi 3 -type structure. A magnetic phase transition at T N = 3.3 K is assessed using specific heat and ac magnetic susceptibility measurements. No additional anomaly below T N down to 50 mK was detected by performing specific heat measurements. Neutron single crystal diffraction data collected at T = 300 mK confirm the antiferromagnetic phase below T N = 3.3 K with the propagation vector $\vec{\tau}$ = (0.2, 0, 0). Possible magnetic structure solutions of NdCuGa 3 are discussed

36 MATERIALS SCIENCE↗
DOE OSTI2023

Magnetic properties of Lu and Y doped Ce-Fe-B magnets

The growing demand for Nd2Fe14B magnets is exacerbating the current critical materials shortage. To reduce the amount of critical material in Nd2Fe14B magnets, chemical substitutions have been used and shown to improve the magnetic behavior, such as the Curie Temperature TC, anisotropy field Ha, and saturation magnetization MS.

Bretana, Alex↗
DOE OSTI2023

Anisotropic magnetism of the Shastry-Sutherland lattice material BaNd 2 PtO 5

For this work, single crystals were grown and characterized to investigate the physical properties and magnetic ground state of BaNd 2 PtO 5 , a candidate to host physics of the Shastry-Sutherland model. Analysis of single crystal x-ray diffraction data yields an updated crystal structure, similar to the prior report but now in space group P4/mbm. Magnetization and specific heat measurements reveal an antiferromagnetic transition at T N =1.9K and a large magnetic anisotropy with in-plane magnetization much larger than out-of-plane magnetization. Single crystal neutron diffraction at zero field reveals a propagation vector of ($\frac{1}{2}$$\frac{1}{2}$$\frac{1}{2}$) for the magnetic ground state as compared to the ($\frac{1}{2}$$\frac{1}{2}$0) wave vector observed in the related body-centered material BaNd 2 ZnO 5 . The ground state is found to be a fully compensated antiferromagnet with diffraction data well fitted within the magnetic space group P S –1 (BNS setting #2.7). The ordered moment is mostly in the basal plane with nearest neighbors forming ferromagnetic dimers, however it also has a finite out-of-plane component unlike the related easy-plane materials BaNd 2 ZnO 5 and BaNd 2 ZnS 5 . Field-induced transitions are observed below T N when the field is applied within the basal plane, and in-plane anisotropy of the associated critical fields is observed. The magnetization is strongly impacted by misalignment of the field away from high symmetry directions. These results suggest complex magnetic structures may arise in the field-induced states, and they highlight the need for extreme care when studying this and related Shastry-Sutherland materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Search for octupolar order in NpO 2 by neutron powder diffraction

The magnetic structure of neptunium dioxide (NpO 2 ) remains a mystery despite decades of research. We revisited the search for magnetic ordering in NpO 2 by performing a powder neutron diffraction experiment at low temperatures and relatively large values of Q. Diffraction data were collected for 300 MK, 15 K, and 35 K to understand the phase transition near 25 K. However, no significant changes in the neutron diffraction pattern were identified. Using the octupolar magnetic form factor j 6 , the maximum theoretical expected value of the magnetic moment (3.27 μ B ), the calculated magnetic Bragg peak intensities would not be observable in neutron powder diffraction data. This value is much larger than the previously estimated magnetic moment of ~0.1 μ B . In conclusion, supported by experimental results, these calculations suggest that unpolarized neutron powder diffraction is unsuitable for measuring octupolar ordering in NpO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Magnetic Interactions of the Centrosymmetric Skyrmion Material Gd 2 PdSi 3

The experimental realization of magnetic skyrmion crystals in centrosymmetric materials has been driven by theoretical understanding of how a delicate balance of anisotropy and frustration can stabilize topological spin structures in applied magnetic fields. Recently, the centrosymmetric material Gd 2 PdSi 3 was shown to host a field-induced skyrmion crystal, but the skyrmion stabilization mechanism remains unclear. Here, we employ neutron-scattering measurements on an isotopically enriched polycrystalline Gd 2 PdSi 3 sample to quantify the interactions that drive skyrmion formation. Our analysis reveals spatially extended interactions in triangular planes, and large ferromagnetic interplanar magnetic interactions that are modulated by the Pd/Si superstructure. The skyrmion crystal emerges from a zero-field helical magnetic order with magnetic moments perpendicular to the magnetic propagation vector, indicating that the magnetic dipolar interaction plays a significant role. To conclude, our experimental results establish an interaction space that can promote skyrmion formation, facilitating identification and design of centrosymmetric skyrmion materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Review on crystal structures and magnetic properties of RTX 3 materials

The structural and compositional diversity of the RTX 3 family of materials offers various magnetic and thermodynamic properties such as complex magnetic structure, vibronic bound states, heavy-fermions, valence fluctuations, metamagnetism, spin glass behavior, quantum criticality, and unconventional superconductivity. In this study we present an overview of the crystal structures, crystal growth and magnetic properties of RTX 3 compounds as well as a discussion of the relevant physics. The magnetic properties of several compounds of the RTX 3 family still remain unexplored. The compounds with a complex magnetic structure could potentially host exotic topological phases. This review article may help explore exotic magnetic properties such as the vibron state and topological spin textures.

quantum materials↗
DOE OSTI2022

Magnetic properties of Fe-substituted NiBr 2 single crystals

NiBr 2 is a multiferroic material with an incommensurate magnetic ground state that has easy-plane anisotropy. This manuscript reports how the magnetic properties evolve with Fe substitution in Ni 1-x Fe x Br 2 single crystals for 0 0.17. A particular emphasis is placed on the = 0.055 crystal, for which magnetic phase diagrams were developed on the basis of anisotropic magnetization measurements. The observed phase evolution reveals a phase transition in the x = 0.055 crystal that is not present in NiBr 2 . The data also demonstrate that the easy-plane anisotropy of NiBr is altered by Fe substitution, with a finite easy-axis anisotropy developing at even the low concentration of x = 0.055. Overall, these results demonstrate that Fe substitution enables a fine-tuning of the magnetism in NiBr 2 , especially the magnetic anisotropy, and may therefore promote complex magnetic phases.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Unconventional magnetic order emerging from competing energy scales in the new R Rh 3 Si 7 intermetallics ( R = Gd-Yb)

The competition between Ruderman-Kittel-Kasuya-Yosida (RKKY), crystal electric field (CEF), and Kondo energy scales has recently emerged at the heart of complex magnetism in several Ce- or Yb-based intermetallics. Hard axis magnetic order has been observed in a handful of these compounds, independent of the crystal symmetry, size of the ordered moment, or the relative scale of the Kondo and magnetic ordering temperatures. This raises the question of the role of each energy scale in driving the ground state properties. In focusing on a single class of compounds, the rhombohedral RRh 3 Si 7 , we compare the anisotropy and magnetic ground states in members of this series with only RKKY interactions (R = Gd), or RKKY and CEF effects (R = Tb-Tm), with the behavior of the R = Yb compound, where all three energy scales (RKKY, CEF, Kondo) are at play. Moreover, we extend the comparison to two other isostructural Kondo systems YbIr 3 Si 7 and YbIr 3 Ge 7 , where hard axis magnetic order is also observed. The non-Kondo compounds RRh 3 Si 7 (R = Tb-Tm) lack the complexity of magnetic order along the hard CEF axis, pointing to the dominant role of the Kondo effect in driving this magnetic order. Furthermore, the CEF-RKKY competition is still responsible for complex magnetic ground states, and it appears that the electronic and magnetic degrees of freedom are entangled in all magnetic members of this series of compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Complex magnetic phases in the polar tetragonal intermetallic NdCoGe 3

Polar materials can host a variety of topologically significant magnetic phases, which often emerge from a modulated magnetic ground state. Relatively few noncentrosymmetric tetragonal materials have been shown to host topological spin textures and new candidate materials are necessary to expand the current theoretical models. This manuscript reports on the anisotropic magnetism in the polar, tetragonal material NdCoGe 3 via thermodynamic and neutron diffraction measurements. The previously reported H - T phase diagram is updated to include several additional phases, which exist for both H = 0 and with an applied field H ⊥ c . Neutron diffraction data reveal that the magnetic structures below T N 1 = 3.70 K and T N 2 = 3.50 K are incommensurate, with a ground-state magnetic order that is incommensurate in all directions with the propagation vector $\vec{k}$ = (0.494, 0.0044, 0.385) at 1.8 K. A unique magnetic structure solution is not achievable, but the possible single-$\vec{k}$ and $\vec{k}$ spin models are discussed. These results demonstrate that NdCoGe 3 hosts complicated magnetic order derived from modulated magnetic moments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Van Hove singularity in the magnon spectrum of the antiferromagnetic quantum honeycomb lattice

In quantum magnets, magnetic moments fluctuate heavily and are strongly entangled with each other, a fundamental distinction from classical magnetism. Here, with inelastic neutron scattering measurements, we probe the spin correlations of the honeycomb lattice quantum magnet YbCl 3 . A linear spin wave theory with a single Heisenberg interaction on the honeycomb lattice, including both transverse and longitudinal channels of the neutron response, reproduces all of the key features in the spectrum. In particular, we identify a Van Hove singularity, a clearly observable sharp feature within a continuum response. The demonstration of such a Van Hove singularity in a two-magnon continuum is important as a confirmation of broadly held notions of continua in quantum magnetism and additionally because analogous features in two-spinon continua could be used to distinguish quantum spin liquids from merely disordered systems. These results establish YbCl 3 as a benchmark material for quantum magnetism on the honeycomb lattice.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Weakly coupled alternating S = 1 2 chains in the distorted honeycomb lattice compound Na 2 Cu 2 TeO 6

Spin- 1 2 chains with alternating antiferromagnetic (AF) and ferromagnetic (FM) couplings exhibit quantum entanglement as the integer-spin Haldane chains and might be similarly utilized for quantum computations. Such alternating AF-FM chains have been proposed to be realized in the distorted honeycomb lattice compound Na 2 Cu 2 TeO 6 , but to confirm this picture a comprehensive understanding of the exchange interactions including terms outside of the idealized model is required. Here, we employ neutron scattering to study the spin dynamics in Na 2 Cu 2 TeO 6 and accurately determine the coupling strengths through the random phase approximation and density functional theory approaches. We find the AF and FM intrachain couplings are the dominant terms in the spin Hamiltonian, while the interchain couplings are AF but perturbative. This hierarchy in the coupling strengths and the alternating signs of the intrachain couplings can be understood through their different exchange paths. Our results establish Na 2 Cu 2 TeO 6 as a weakly coupled alternating AF-FM chain compound and reveal the robustness of the gapped ground state in alternating chains under weak interchain couplings.

1-dimensional spin chains↗