139,398 research outputs found
TWO EXOTIC AND UNIQUE FAMILIES OF RARE EARTH INTERMETALLIC COMPOUNDS
No full textThe rare earth metals form two unique, one of a kind, families of intermetallic compounds. One family crystallizes in the simple cubic CsCl, B2-type structure with 2 atoms in the unit cell; while the second family has the complex orthorhombic Nd11Pd4In9-type structure with 48 atoms in the unit cell. The first family, the RM compounds with the B2-type structure,
where R is a rare earth metal and M = Cu, Ag, and Au, are ductile phases. Some non-rare earths containing B2 phases have also been studied and most were found to follow the criteria for ductility/brittleness established by the RM phases. The second family, the R11M4In9 phases where M = Ni, Pd and Pt, form a fibrous microstructure.
The microstructure is self-assembled
directly from the melt (whether rapidly or slow cooled) and is probably due to the large aspect
ratio of 6.0 for the b/c lattice parameter ratio and the very short In-In bonds in the a-b plane
which give rise to kinetic hindrance during solidifying and prevent the crystal from growing in
the a and b directions
Synthesis and magnetic properties of LaFe13-x-yMxSiyN3 nitrides
No full textSingle-phase LaFe13-x-yMxSiyN3 compounds (M = Mn) were synthesized by subjecting intermetallic precursors to the ammonia flow at 623 K for 4 h. The nitrides derived from Si-poor (y ≤ 3) cubic intermetallics retain the NaZn13-type crystal structure and show considerable (~3 %) lattice expansion compared to the nitrogen-free materials. The temperatures of the magnetic ordering transitions, all of which are second order, increase by ~ 200 K as a result of nitrogenation, and all nitrides exhibit rather weak and broad magnetocaloric effects. The nitrides are stable below 750 K, but they begin to lose nitrogen above this temperature, fully decomposing above 1050 K. The nitrogenation of the tetragonal LaFe9Si4 results in the decomposition of the intermetallic phase and formation of the Fe3N compound together with unidentified amorphous phase(s).This is a manuscript of an article published as Thayer, A., I. Hlova, Y. Mudryk, X. Liu, and V. K. Pecharsky. "Synthesis and magnetic properties of LaFe13-x-yMxSiyN3 nitrides." Journal of Alloys and Compounds 920 (2022): 165927.
DOI: 10.1016/j.jallcom.2022.165927.
Copyright 2022 Elsevier B.V.
Posted with permission.
DOE Contract Number(s): AC02-07CH11358
The nano-microfibrous R11Ni4In9 intermetallics: New compounds and extraordinary anisotropy in Tb11Ni4In9 and Dy11Ni4In9
No full textR11Ni4In9 (R = rare earth) compounds exhibit an unusual self-assembled nano/microfibrous morphology that results in anisotropic structural
and magnetic behaviors. The existence of new compounds for R = Dy, Ho, Er, Tm and Lu, has been established (orthorhombic Nd11Pd4In9-
type, oC48, Cmmm, Z = 2), showing that the formation of these phases, previously known for R = La–Nd, Sm, Gd, Tb and Y, extends to all of the
rare earth elements, except Sc, Eu and Yb. The results of physical property measurements performed on oriented fibers of Tb11Ni4In9, Dy11Ni4In9
and Y11Ni4In9 are presented. Multiple magnetic transitions are observed in Tb11Ni4In9 and Dy11Ni4In9 with the highest ordering temperature, TC, of
112 and 88 K, respectively. Y11Ni4In9 is a Pauli paramagnet down to 2 K. The fibrous microstructure of these compounds leads to a strong anisotropy
in their electrical resistivity and magnetization behaviors. The c-axis of the orthorhombic cell is the easy magnetization and high electrical-conductivity
direction. Ferrimagnetic-like behavior, with extremely high coercive fields (HC = 6.6 T for Tb11Ni4In9 at 5 K and HC = 5.7 T for
Dy11Ni4In9 at 2 K), is found when the fibers (and the c-axis) are oriented parallel to the magnetic field direction; antiferromagnetic-like ground state
is observed with the fibers oriented orthogonal (i.e., in the a–b plane). Appearance of a Griffiths phase regime is observed in both compounds before
entering the ordered magnetic states. This is more evident for fibers orthogonal to the magnetic field and is even preserved at 1 T. Field induced spinflop
magnetic transitions are also observed in Tb11Ni4In9 and Dy11Ni4In9 with fibers orthogonal and parallel to the field, respectively. First principles
calculations have been performed for several representative compounds to explain the underlying phase stability and their magnetism
Inducing Fe moment in LaFeSi with p-block element substitution
No full textWe studied the LaFeSi phase using density functional theory based full-potential linearized augmented plane wave (FP-LAPW) method. Specifically we examined the effect of p-element substitution on the stability and magnetic properties focusing on pathways to induce Fe magnetic moments. We demonstrate that either partial or complete substitutions at the Si 2 c-site by several p-block elements lead to non-zero Fe moments. Our theoretical study shows that partially substituted LaFeSi 1-y Ga y and LaFeSi 1-y Al y are more thermodynamically stable than the fully substituted LaFeGa and LaFeAl. We also found that the P substitutions, either partial or complete, have the most negative formation energies, however the compounds containing phosphorus are non-magnetic. Our work highlights a pathway toward manipulations of the otherwise quenched Fe-moments in LaFeSi-related compounds and help in advancing the potential magnetic functionalities of LaFeX compounds.This article is published as Chouhan, Rajiv K., Tyler J. Del Rose, Yaroslav Mudryk, and Vitalij K. Pecharsky. "Inducing Fe moment in LaFeSi with p-block element substitution." AIP Advances 12, no. 3 (2022): 035130.
DOI: 10.1063/9.0000334.
Copyright 2022 The Author(s).
Attribution 4.0 International (CC BY 4.0).
Posted with permission.
DOE Contract Number(s): AC02-07CH11358
Magnetic and transport behaviors of non-centrosymmetric Nd7Ni2Pd
No full textCrystallographic, magnetic, electrical transport and thermodynamic properties of pseudo-binary Nd7Ni2Pd compound have been studied using temperature-dependent x-ray powder diffraction and physical property measurements. Compared to the ferromagnetic parent Nd7Pd3, the ground state of Nd7Ni2Pd is antiferromagnetic, and it exhibits strong metamagnetism. The measurements indicate two antiferromagnetic transitions in fields less than 8 kOe: a second-order paramagnetic to antiferromagnetic at TN2 = 29 K and a weak first-order antiferromagnetic to antiferromagnetic transition at TN1 = 24.5 K. The compound becomes ferromagnetic in fields of 8 kOe and higher with TC = 30 K. Temperature dependence of lattice parameters is anomalous, most prominently in the basal plane at ∼30 K; however, there is no detectable structural distortion or clear volume discontinuity around 25 K, suggesting a significant weakening of the first-order transition when compared to the binary Nd7Pd3.</p
Spatially-localized time dependent solutions including turbulence and their interactions in 2D Kolmogorov flow
No full textIn 2D Kolmogorov flow in small aspect ratio domains, spatially-localized solutions such as kink, traveling or time-dependent kink-antikink pars coexist. However, the conservation of the flow rate in the y direction strongly restrict combination of localized solutions and their positioning. We find that by adding a homogeneous flow U y their positioning is controlled and each of localized solutions including a spatially-localized chaos is isolated. Numerical results suggest that these isolated solutions can be elements constructing a whole flow
Characteristics of overlap region in high-Reynolds number turbulent channel flow
No full textDirect numerical simulation of the fully developed turbulent channel flows have been carried out at the Reynolds number based on the friction velocity and the channel half width, 2000, 4000 and 8000. A hybrid 10th order accurate finite difference scheme in the stream and spanwise directions, and a second-order scheme in the wall-normal direction is adapted as the spatial discretization method. We observed the plateau profiles in the indicator function corresponded to the von Karman constant. Furthermore, second peak of streamwise pre-multiplied spectra were appeared in the same wall normal height, 300 < y+ < 600, in case of Re = 4000. Nevertheless, the effects of the lager than the channel half height scale on the streamwise turbulent intensity are fixed contributions without dependence on Reynolds number. These results suggested that the new streamwise vortexes are formed between buffer layer and outer layer with increasing of Reynolds number
Correlating Crystallography, Magnetism, and Electronic Structure Across Anhysteretic First-Order Phase Transition in Pr2In
No full textTemperature-dependent powder X-ray diffraction and magnetization measurements of Pr2In conclusively prove that the unusual anhysteretic first-order paramagnetic-ferromagnetic phase transition in the compound is related to concurrent changes in both the magnetic and crystallographic lattices. At the same time, the hexagonal Ni2In-type structure is stable at least between 6 and 298 K, including at TC = ∼57 K. From the density functional theory calculations, the electronic structure of the compound is extraordinarily sensitive to minor changes in lattice parameters that occur across the phase transition, revealing the origin of strong magnetoelastic coupling. In the vicinity of TC, the maximum entropy change, ΔSMax = −16 J Kg−1 K−1 induced by a moderate magnetic field change of 20 kOe (ΔSMax = −20 J Kg−1 K−1 for 50 kOe magnetic field change) is comparable to other known potentially functional materials demonstrating large cryogenic magnetocaloric effect.This is a manuscript of an article published as Biswas, Anis, Rajiv K. Chouhan, O. Dolotko, A. Thayer, S. Lapidus, Y. Mudryk, and V. K. Pecharsky. "Correlating Crystallography, Magnetism, and Electronic Structure Across Anhysteretic First-Order Phase Transition in Pr2In." ECS Journal of Solid State Science and Technology 11, no. 4 (2022): 043005.
DOI: 10.1149/2162-8777/ac611d.
Copyright 2022 IOP Publishing Ltd.
Posted with permission.
DOE Contract Number(s): AC02-07CH11358; AC02-06CH11357
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