Evidence of homogeneous intermediate valence coexisting with long-range magnetic order in EuCu2(Si,Ge)2
P. S. Savchenkov+, V. A. Sidorov*, J. Guo×, L. Sun×, P. A. Alekseev+°
+National Research Centre "Kurchatov Institute", 123182 Moscow, Russia
*Vereshchagin Institute of High Pressure Physics, Russian Academy of Sciences, 108840 Troitsk, Moscow, Russia
×Institute of Physics, Chinese Academy of Sciences, 100190 Beijing, People's Republic of China
°National Research Nuclear University MEPhI, 115409 Moscow, Russia
Abstract
The phase diagram of the intermediate valence system EuCu2Ge2 is investigated by
measuring the temperature dependencies of the heat capacity and the electrical resistance as a
function of pressure up to 15 GPa. Transition to the magnetic ordered state is observed at
pressures up to 9 GPa. It is established that for EuCu2Ge2 system the effects of the hydrostatic
and chemical (substitution of Ge for Si) pressure on Eu-valence are equivalent from the point of
view of the transition to the antiferromagnetic ordered ground state. The coexistence of the
homogeneous intermediate valence state and long-range magnetic order in EuCu2(Si,Ge)2 has
been confidently established. The magnetic phase diagram is presented as a function of Eu
average valence. The probable background for the formation of the magnetically ordered
intermediate valence state of Eu is considered. There is an indication that it develops on the basis
of competition of the two magnetic configurations of Eu, in some analogy with the case of TmSe
intermediate valence system.