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Title: Electric Transport in R2MGe6 Ternary Compounds (R=La, Ce, Gd, Tb, Dy, Ho; M=Mn, Ni, Cu)

Abstract

Polycrystalline samples of the intermetallic compounds La{sub 2}MnGe{sub 6}, Ce{sub 2}MnGe{sub 6}, La{sub 2}CuGe{sub 6}, Ce{sub 2}CuGe{sub 6}, and R{sub 2}NiGe{sub 6} (R = Gd, Tb, Dy, Ho), which belong to the Ce{sub 2}CuGe{sub 6} type of structure (Amm2 or Cm2m space group), were studied by means of the electrical resistivity and differential thermopower measurements. They exhibit the metallic-like behavior in the temperature range from 5 to 290 K. The peculiarities in both resistivity and thermopower temperature dependencies correlate with corresponding magnetic transition T{sub tr} temperatures.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Ames Laboratory (AMES), Ames, IA
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
941102
Report Number(s):
IS-J 7334
Journal ID: ISSN 0925-8388; JALCEU; TRN: US200824%%545
DOE Contract Number:
DE-AC02-07CH11358
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Alloys and Compounds; Journal Volume: 459
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; ELECTRIC CONDUCTIVITY; INTERMETALLIC COMPOUNDS; TRANSPORT

Citation Formats

M. Konyk, B. Kuzhel, Yu. Stadnyk, Yu. Gorelenko, Ya. Mudryk, and A. Waskiv. Electric Transport in R2MGe6 Ternary Compounds (R=La, Ce, Gd, Tb, Dy, Ho; M=Mn, Ni, Cu). United States: N. p., 2007. Web.
M. Konyk, B. Kuzhel, Yu. Stadnyk, Yu. Gorelenko, Ya. Mudryk, & A. Waskiv. Electric Transport in R2MGe6 Ternary Compounds (R=La, Ce, Gd, Tb, Dy, Ho; M=Mn, Ni, Cu). United States.
M. Konyk, B. Kuzhel, Yu. Stadnyk, Yu. Gorelenko, Ya. Mudryk, and A. Waskiv. Sun . "Electric Transport in R2MGe6 Ternary Compounds (R=La, Ce, Gd, Tb, Dy, Ho; M=Mn, Ni, Cu)". United States. doi:.
@article{osti_941102,
title = {Electric Transport in R2MGe6 Ternary Compounds (R=La, Ce, Gd, Tb, Dy, Ho; M=Mn, Ni, Cu)},
author = {M. Konyk and B. Kuzhel and Yu. Stadnyk and Yu. Gorelenko and Ya. Mudryk and A. Waskiv},
abstractNote = {Polycrystalline samples of the intermetallic compounds La{sub 2}MnGe{sub 6}, Ce{sub 2}MnGe{sub 6}, La{sub 2}CuGe{sub 6}, Ce{sub 2}CuGe{sub 6}, and R{sub 2}NiGe{sub 6} (R = Gd, Tb, Dy, Ho), which belong to the Ce{sub 2}CuGe{sub 6} type of structure (Amm2 or Cm2m space group), were studied by means of the electrical resistivity and differential thermopower measurements. They exhibit the metallic-like behavior in the temperature range from 5 to 290 K. The peculiarities in both resistivity and thermopower temperature dependencies correlate with corresponding magnetic transition T{sub tr} temperatures.},
doi = {},
journal = {Journal of Alloys and Compounds},
number = ,
volume = 459,
place = {United States},
year = {Sun Apr 29 00:00:00 EDT 2007},
month = {Sun Apr 29 00:00:00 EDT 2007}
}
  • Ternary compounds REAgSb{sub 2}, RE = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, have been synthesized by arc melting followed by a heat treatment at 600 or 800{degrees}C for 300 hr. The novel phases were all found to be isotypic with the structure type of ZrCuSi{sub 2}. Precise atom parameters have been derived for CeAgSb{sub 2} from X-ray single crystal counter data: space group P4/nmm, a = 0.43641(9) nm, c = 1.0722(4) nm, and Z = 2. For 274 reflections ({vert_bar}F{sub o}{vert_bar} > 3{sigma}) the residual values are R{sub F} = {Sigma}{vert_bar}{Delta}F{vert_bar}/{Sigma}{vert_bar}F{sub o}{vert_bar} = 0.024more » and R{sub w} = 0.028. A standardized set of atom parameters is provided. Magnetism of the REAgSb{sub 2} phases in the temperature range 2.5 to 300 K is characterized by tripositive paramagnetic behavior of the rare-earth atoms. REAgSb{sub 2} with RE = Y, La are weakly temperature-dependent paramagnets. In contrast, REAgSb{sub 2} compounds with RE = Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm are weak antiferromagnets with ordering temperatures lower than T{sub N} {approximately} 13 K, and CeAgSb{sub 2} is a noncolinear antiferromagnet (T{sub M} {approximately} 12 K) with a remanent magnetization {mu} = 0.15 {mu}{sub B} per Ce atom.« less
  • The antiferromagnetic transition is investigated in the rare-earth (R) tritelluride RTe{sub 3} family of charge density wave (CDW) compounds via specific heat, magnetization and resistivity measurements. Observation of the opening of a superzone gap in the resistivity of DyTe{sub 3} indicates that additional nesting of the reconstructed Fermi surface in the CDW state plays an important role in determining the magnetic structure.
  • Tm/sub 3/Cu/sub 4/Sn/sub 4/ has been studied by single - crystal X - ray diffraction analysis. The structure is of a new type with space group C2/m and Z = 2 : a = 16.119(2), b = 4.3935(6), c = 6.896(1) A, ..beta.. = 115.88(2)/sup 0/, D /SUB x/ = 9.32 Mgm/sup -3/, ..mu..(MoK..cap alpha..) = 52 mm/sup -1/, F(000) = 1045, R = 0.056 for 558 independant reflexions (R /SUB w/ = 0.058). Tm/sub 3/Cu/sub 4/Sn/sub 4/ is a monoclinic distorded variety of the Gd/sub 3/Cu/sub 4/Ge/sub 4/ structure typ0e. Seven other compounds were characterized : Sc/sub 3/Cu/sub 4/Ge/submore » 4/ and R.E/sub 3/Cu/sub 4/Sn/sub 4/ where R.E. = Y, Gd, Tb, Dy, Ho, Er, isostructural with Gd/sub 3/Cu/sub 4/Sn/sub 4/.« less
  • Crystals of nonstoichiometric phases Sr{sub 1-x}R{sub x}F{sub 2+x} (R are 14 rare-earth elements) and the ordered phase Sr{sub 4}Lu{sub 3}F{sub 17} with a trigonally distorted fluorite lattice were grown by the Bridgman method. Ten of 26 Sr{sub 1-} {sub x}R{sub x}F{sub 2+x} crystals, where R = La-Ho or Y, melt congruently. The isoconcentration series Sr{sub 0.90}R{sub 0.10}F{sub 2.10} includes four crystals with R = Er-Lu. The compositions corresponding to the maxima for the latter crystals were not determined. The concentration series, in which the mole fraction of RF{sub 3} varies from 10 to 50 mol %, were obtained for themore » crystals with R = La, Nd, and Gd. Most of the crystals are of good optical quality. To evaluate the composition changes in the course of crystal growth, the cubic unit-cell parameters were determined by X-ray powder diffraction. The line-broadening analysis revealed a nonmonotonic change of microdistortions as regards both the rare-earth content and rare-earth series. The changes in the lattice parameters and the congruent-melting points of the Sr{sub 1-x}R{sub x}F{sub 2+x} phases in the rare-earth series reflect the morphotropic transitions in the series of pure RF{sub 3} despite the fact that SrF{sub 2} dominates in nonstoichiometric fluorite crystals.« less
  • The crystal structure of new Mo{sub 2}NiB{sub 2}-type (Gd, Tb, Dy){sub 2}Ni{sub 2.35}Si{sub 0.65} (Immm, No. 71, oI10) and La{sub 2}Ni{sub 3}-type (Dy, Ho){sub 2}Ni{sub 2.5}Si{sub 0.5} (Cmce No. 64, oC20) compounds has been established using powder X-ray diffraction studies. Magnetization measurements show that the Mo{sub 2}NiB{sub 2}-type Gd{sub 2}Ni{sub 2.35}Si{sub 0.65} undergoes a ferromagnetic transition at ~66 K, whereas isostructural Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} shows an antiferromagnetic transition at ~52 K and a field-induced metamagnetic transition at low temperatures. Neutron diffraction study shows that, in zero applied field, Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} exhibits c-axis antiferromagnetic order with propagation vectormore » K=[1/2, 0, 1/2] below its magnetic ordering temperature and Tb magnetic moment reaches a value of 8.32(5) μ{sub B} at 2 K. The La{sub 2}Ni{sub 3}-type Dy{sub 2}Ni{sub 2.5}Si{sub 0.5} exhibits ferromagnetic like transition at ~42 K with coexisting antiferromagnetic interactions and field induced metamagnetic transition below ~17 K. The magnetocaloric effect of Gd{sub 2}Ni{sub 2.35}Si{sub 0.65}, Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} and Dy{sub 2}Ni{sub 2.5}Si{sub 0.5} is calculated in terms of isothermal magnetic entropy change and it reaches a maximum value of −14.3 J/kg K, −5.3 J/kg K and −10.3 J/kg K for a field change of 50 kOe near 66 K, 52 K and 42 K, respectively. Low temperature magnetic ordering with enhanced anisotropic effects in Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} and Dy{sub 2}Ni{sub 2.35}Si{sub 0.65} is accompanied by a positive magnetocaloric effect with isothermal magnetic entropy changes of +12.8 J/kg K and ~+9.9 J/kg K, respectively at 7 K for a field change of 50 kOe. - Graphical abstract: The (Gd, Tb, Dy){sub 2}Ni{sub 2.35}Si{sub 0.65} supplement the series of Mo{sub 2}NiB{sub 2}-type rare earth compounds, whereas the (Dy, Ho){sub 2}Ni{sub 2.5}Si{sub 0.5} supplement the series of La{sub 2}Ni{sub 3}-type rare earth compounds. The variation of alloy’s composition by ~3 at% i.e. from Dy{sub 2}Ni{sub 2.35}Si{sub 0.65} to Dy{sub 2}Ni{sub 2.5}Si{sub 0.5} leads to significant transformation of crystal structure of compound with different variant of distortion of Po-type rare earth sublattice, as in Gd–Co–Ga and Er–Ni–In systems: the Mo{sub 2}NiB{sub 2}-type Gd{sub 2}Co{sub 2}Ga and La{sub 2}Ni{sub 3}-type Gd{sub 2}Co{sub 2.9}Ga{sub 0.1}, and Mo{sub 2}FeB{sub 2}-type Er{sub 2}Ni{sub 1.78}In and Mn{sub 2}AlB{sub 2}-type Er{sub 2}Ni{sub 2}In. Magnetization measurements indicate collinear ferromagnetic ordering of Mo{sub 2}NiB{sub 2}-type Gd{sub 2}Ni{sub 2.35}Si{sub 0.65} and a complex antiferromagnetic ordering with low-temperature metamagnetic nature for Mo{sub 2}NiB{sub 2}-type Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} compounds. However, neutron diffraction study in zero applied field of Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} reveals c-axis pure antiferromagnetic ordering of terbium sublattice with K=[1/2, 0, 1/2] propagation vector. Magnetization measurements indicate ferromagnetic order with coexisting antiferromagnetic interactions and low-temperature metamagnetic state for La{sub 2}Ni{sub 3}-type Dy{sub 2}Ni{sub 2.5}Si{sub 0.5}. We suggest possible polymorphism in other Mo{sub 2}FeB{sub 2}-type, Mo{sub 2}NiB{sub 2}-type, La{sub 2}Ni{sub 3}-type and Mn{sub 2}AlB{sub 2}-type rare earth compounds with corresponding change in their magnetic properties. - Highlights: • (Gd, Tb, Dy){sub 2}Ni{sub 2.35}Si{sub 0.65} compounds crystallize in the Mo{sub 2}NiB{sub 2}-type structure. • (Dy, Ho){sub 2}Ni{sub 2.5}Si{sub 0.5} compounds crystallize in the La{sub 2}Ni{sub 3}-type structure. • Gd{sub 2}Ni{sub 2.35}Si{sub 0.65} shows pure ferromagnetic type ordering. • Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} and Dy{sub 2}Ni{sub 2.5}Si{sub 0.5} show mixed ferro-antiferromagnetic ordering. • Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} and Dy{sub 2}Ni{sub 2.5}Si{sub 0.5} exhibit low-temperature metamagnetic behaviour.« less