On the problem of the valence determination of Eu in mixed-valence compounds EuCu2Si2and EuPd2Si2

Abd‐Elmeguid, M. M.; Sauer, Ch.; Zinn, W.

doi:10.1088/0022-3719/18/2/012

Cited by 27 publications

(8 citation statements)

References 10 publications

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“…In contrast to the Mössbauer spectra of a polycrystalline EuCu 2 Si 2 [1,4,5], the spectra of the studied specimen consist of one line located at ∼−8.65 mm/s. This shows that Eu is divalent and there are no signs of valence fluctuations in the temperature range 77.5-299.5 K.…”

Section: Resultsmentioning

confidence: 82%

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Absence of charge fluctuations of europium in metallic single crystals of EuCu2Si2

et al. 2006

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The 151 Eu Mössbauer effect study in the temperature range 2.2-299.5 K on pulverized single crystals of EuCu 2 Si 2 synthesized from an indium flux is presented. In contrast to previous studies on polycrystalline samples in which valence fluctuations for Eu were reported, we find that the Eu atoms are divalent in the whole temperature range. Therefore, there are no charge fluctuations of Eu in EuCu 2 Si 2 .

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Section: Resultsmentioning

confidence: 82%

“…It is evident that δ changes very little with temperature and its value proves that Eu in EuCu 2 Si 2 is divalent in the temperature range 2.2-299. 5 …”

Section: Resultsmentioning

confidence: 99%

Absence of charge fluctuations of europium in metallic single crystals of EuCu2Si2

et al. 2006

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“…In the case of Eu based rare earth intermetallic compounds such as EuPd 2 Si 2 and EuCu 2 Si 2 , a minor phase has been observed which also orders magnetically at low temperatures with a slightly lower Eu valence than in the main phase. [24,25,26] To further investigate the effect of the Eu valence on magnetic ordering, we have performed band-structure calculations of the generalized susceptibility χ(q) for different valences of Eu by varying the Fermi energy. In the χ(q) calculation each small tetrahedron contribution (in q space) was weighted by the Eu 5d wavefunction components which are predominantly responsible for coupling the Eu 4f moments via the RKKY mechanism.…”

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confidence: 99%

Magnetic ordering inEuRh2As2studied by x-ray resonant magnetic scattering

Nandi

Kreyßig²,

Lee³

et al. 2009

Phys. Rev. B

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Element-specific x-ray resonant magnetic scattering investigations were performed to determine the magnetic structure of Eu in EuRh 2 As 2 . In the temperature range from 46 K down to the lowest achievable temperature of 6 K, an incommensurate antiferromagnetic ͑ICM͒ structure with a temperature-dependent propagation vector Ϸ͑0 0 0.9͒ coexists with a commensurate antiferromagnetic ͑CM͒ structure. Angulardependent measurements of the magnetic intensity indicate that the magnetic moments lie in the tetragonal basal plane and are ferromagnetically aligned within the a-b plane for both magnetic structures. The ICM structure is most likely a spiral-like magnetic structure with a turn angle of ϳ162°͑0.9͒ between adjacent Eu planes in the c direction. In the CM structure, this angle is 180°. These results are consistent with bandstructure calculations which indicate a strong sensitivity of the magnetic configuration on the Eu valence.The complex interplay among superconductivity, magnetism, and structural instabilities in AFe 2 As 2 ͑A = Ba, Sr, Ca, and Eu͒ pnictides upon chemical substitution or under applied pressure has generated a great deal of recent attention and research activity. 1-7 Related isostructural compounds such as BaRh 2 As 2 , BaMn 2 As 2 , and EuRh 2 As 2 ͑Refs. 8-10͒ have also been synthesized and studied in an attempt to increase significantly superconducting transition temperatures and to understand the role of Fe in the Fe-As layers as well as the A site in promoting superconductivity. The metallic compound EuRh 2 As 2 shows a plethora of interesting physical properties such as giant magnetoresistance and a strong reduction in the electronic specific-heat coefficient with applied field in the antiferromagnetic state. 10 The reported intermediate valence of 2.13͑2͒ for Eu ͑Ref. 10͒ adds further interest as it may be tuned by applied pressure or temperature. 11,12 Since Eu 2+ ions carry a magnetic moment with spin S =7/ 2 while Eu 3+ does not have a permanent magnetic moment, EuRh 2 As 2 may be an excellent model system to study the complex interplay between valence and magnetism in the "122" pnictides.EuRh 2 As 2 crystallizes in the ThCr 2 Si 2 -type tetragonal structure with space group I4 / mmm ͑Ref. 13͒ and lattice parameters a = 4.075 Å and c = 11.295 Å at T = 298 K. 10 Specific-heat and magnetization data indicate that the Eu moments order antiferromagnetically below T N =46 K. 10 The magnetic susceptibility parallel to the c axis increases below T N and decreases when measured perpendicular to the c axis. 10 This indicates that the moments are primarily aligned in the basal a-b plane. Nevertheless, the microscopic details of the magnetic structure are, as yet, unknown. Here, we report on the magnetic ordering of Eu moments in EuRh 2 As 2 studied by x-ray resonant magnetic scattering ͑XRMS͒. 14 For the present measurements, this technique offers several advantages over neutron scattering due to the large neutron absorption cross section of the natural isotope 152 Eu. Moreover, the elemental...

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“…A detailed discussion of this problem is given in [19]. On the other hand, for powder samples the characteristic problem is the presence of the so-called satellite phase where europium is nearly divalent [21]. This satellite phase seems to be common for most IV Eu-based systems with ThCr 2 Si 2 structure [11] and typically contains 10-20% of Eu ions in the sample (for more details see [10,11,21] and references therein).…”

Section: Samples and Experimental Detailsmentioning

confidence: 99%

Magnetic excitations in EuCu₂(Si_xGe_1−x)₂: from mixed valence towards magnetism

Alekseev¹,

Nemkovski²,

Mignot³

et al. 2012

J. Phys.: Condens. Matter

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We report the inelastic neutron scattering study of spin dynamics in EuCu(2)(Si(x)Ge(1-x))(2) (x = 1, 0.9, 0.75, 0.6), performed in a wide temperature range. At x = 1 the magnetic excitation spectrum was found to be represented by the double-peak structure well below the energy range of the Eu(3+) spin-orbit (SO) excitation (7)F(0)→(7)F(1), so that at least the high-energy spectral component can be assigned to the renormalized SO transition. Change of the Eu valence towards 2 + with increased temperature and/or Ge concentration results in further renormalization (lowering the energy) and gradual suppression of both inelastic peaks in the spectrum, along with developing sizeable quasielastic signal. The origin of the spectral structure and its evolution is discussed in terms of excitonic model for the mixed valence state.

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On the problem of the valence determination of Eu in mixed-valence compounds EuCu₂Si₂and EuPd₂Si₂

Cited by 27 publications

References 10 publications

Absence of charge fluctuations of europium in metallic single crystals of EuCu2Si2

Absence of charge fluctuations of europium in metallic single crystals of EuCu2Si2

Magnetic ordering inEuRh2As2studied by x-ray resonant magnetic scattering

Magnetic excitations in EuCu₂(Si_xGe_1−x)₂: from mixed valence towards magnetism

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On the problem of the valence determination of Eu in mixed-valence compounds EuCu2Si2and EuPd2Si2

Cited by 27 publications

References 10 publications

Absence of charge fluctuations of europium in metallic single crystals of EuCu2Si2

Absence of charge fluctuations of europium in metallic single crystals of EuCu2Si2

Magnetic ordering inEuRh2As2studied by x-ray resonant magnetic scattering

Magnetic excitations in EuCu2(SixGe1−x)2: from mixed valence towards magnetism

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On the problem of the valence determination of Eu in mixed-valence compounds EuCu₂Si₂and EuPd₂Si₂

Magnetic excitations in EuCu₂(Si_xGe_1−x)₂: from mixed valence towards magnetism