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

Abstract

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.

Europium mixed-valence, long-range magnetic order, and dynamic magnetic response in EuCu2(SixGe1−x)2Nemkovski1, Козленко2, Alekseev3 et al. 2016Phys. Rev. B301140View full textAdd to dashboardCite

“…42) and EuCu 2 Si 1.8 Ge 0.2 (Ref. 33), but strongly damped, as is commonly observed in the HF regime, [43][44][45] to which this compound is thought to belong. The magnetic QE signal has a Lorentzian lineshape with a full width at half maximum (FWHM) Γ of about 1.5 meV.…”

“…To avoid complications due to the spingap formation in the Si-rich compounds at low temperature, we focus on the QE response in the temperature region 100 ≤ T ≤ 200 K. The values of Γ derived from the present data are plotted in Fig. 5(a), together with those obtained previously 33 for EuCu 2 Si 2 and EuCu 2 Si 1.8 Ge 0.2 , as a function of the Si concentration x. For x = 0.4, the linewidth is too small to be measured precisely within instrumental resolution.…”

“…Its existence contrasts with the spin-gap response observed 33,42 below 100-150 K for compositions x > 0.75, and reflects a qualitative change in the energy spectrum of spin fluctuations. With increasing temperature, the QE linewidth gradually increases to exceed 3 meV at 100 K. This broadening, however, remains limited in comparison with the linewidths of 10 meV or more observed above 150 K in the Si-rich compounds 33,42 [ Fig. 5(a)].…”

“…33 All spectra have been reduced to Q = 0 according to the magnetic form factor for the 7 F 0 → 7 F 1 spin-orbit transition of Eu 3+ . The sample with the higher Si content (x = 0.75) is located above the critical concentration x c = 0.65 in the phase diagram, 23 and thus does not order magnetically.…”

Valence fluctuation and magnetic ordering in EuNi2(P1−xGex)2single crystals

“…7,8 We present the the crystal growth of EuNi 2 (P 1−x Ge x ) 2 and study the evolution from valencefluctuating EuNi 2 P 2 to divalent Eu upon increasing Ge doping. One advantage of substituting Ge for P instead of e.g.…”