Intermediate-valence state of the Sm and Eu in SmB₆and EuCu₂Si₂: neutron spectroscopy data and analysis

Abstract

The analysis of the magnetic neutron scattering data for Sm (SmB<sub>6</sub>, Sm(Y)S) and Eu (EuCu<sub>2</sub>Si<sub>2-x</sub>Ge<sub>x</sub>) intermediate valence compounds has been performed in terms of generalized model of the intermediate-radius exciton. A special attention is drawn to the correlation between average ion's valence and parameters of the low energy excitation in the neutron spectra, such as resonance mode, including its magnetic form factor. Along with specific features of the intermediate valence state formation for Sm and Eu ions, common physical mechanisms have been revealed for the systems based on these elements from the middle part of the rare-earth series. The consistent description of the existing experimental data has been obtained by using a loosely bound hole concept for Eu <i>f</i>-electron shell in the intermediate valence state, in analogy with previously established loosely bound electron model for Sm ion.

Crystal Growth by the Floating Zone Method of Ce-Substituted Crystals of the Topological Kondo Insulator SmB6

“…The results, given in Table 2, reveal that Sm 1−x Ce x B 6 are mixed valence systems, similar to the parent compound SmB 6 [37,38]. The average Sm valence values of the Sm 1−x Ce x B 6 boules are slightly larger than the values determined previously for pure SmB 6 [67][68][69][70], due to surface oxidation effects (an increased concentration of Sm 3+ to the detriment of the Sm 2+ ions). Previous XPS results reported an increased average Sm valence and a B/Sm ratio lower than the nominal stoichiometric value of 6:1 when the SmB 6 crystals were exposed to ambient conditions [67].…”

Advances on topological materials

“…The results, given in Table 2, reveal that Sm 1−x Ce x B 6 are mixed valence systems, similar to the parent compound SmB 6 [37,38]. The average Sm valence values of the Sm 1−x Ce x B 6 boules are slightly larger than the values determined previously for pure SmB 6 [67][68][69][70], due to surface oxidation effects (an increased concentration of Sm 3+ to the detriment of the Sm 2+ ions). Previous XPS results reported an increased average Sm valence and a B/Sm ratio lower than the nominal stoichiometric value of 6:1 when the SmB 6 crystals were exposed to ambient conditions [67].…”

Uncommon Magnetism in Rare-Earth Intermetallic Compounds with Strong Electronic Correlations

“…It should be noted that, in a number of similar neutron experiments with other intermediate-valence compounds based on SmB 6 [57,61,69], where f 6 ( 7 F 0 ) configuration is involved in the formation of the IV state of Sm, no renormalisation of the spin-orbit splitting of the f 6 electron shell with a change in the valence of the rare-earth ion was observed. This suggests a fundamental difference [61] in the conditions for the formation of IV states in europium (due to hybridisation) and samarium (due to Coulomb interaction) compounds.…”

“…It is important to note that in the "classical" intermediate-valence compound SmB 6 (ν ≈ 2.5), one of the "competing" configurations (Sm 2+ : 7 F 0 , J = 0), is nonmagnetic, similar to Eu 3+ , and the mechanisms of IV state formation in SmB 6 and EuCu 2 Si 2 are fundamentally similar [61]. However, in related series based on SmB 6 [14,62] with different Sm valencies, coexistence of LRMO and the intermediate-valence states has not been observed.…”