Pis’ma v ZhETF, vol. 114, iss. 9, pp. 608 - 609

Evidence of homogeneous intermediate valence coexisting with

long-range magnetic order in EuCu₂(Si,Ge)₂

P. S. Savchenkov⁺¹⁾, 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

Submitted 17 August 2021

Resubmitted 23 September 2021

Accepted 23 September 2021

DOI: 10.31857/S1234567821210059

The phase diagram of the intermediate valence (IV)

system EuCu₂Ge₂ is investigated by measuring the tem-

perature dependencies of the heat capacity and the elec-

trical resistance as a function of pressure (P ) up to

4 GPa. Measurements were done using “toroid”, Bridg-

man Anvils (BA) and Diamond Anvil Cell (DAC) pres-

sure cells Transition to the magnetic ordered state is

observed at P up to 9 GPa.

The dependence of T_N on pressure according to the

results of all above mentioned experiments is shown in

Fig. 1. The inset in Fig. 1 shows the magnetic phase di-

agram of EuCu₂(Si_xGe_1-x)₂ based on previous experi-

ments [1-3].

The dependence of T_N on pressure, obtained in the

present work qualitatively and quantitatively (by the

Fig. 1. (Color online) Pressure dependence of TN for

value of T_N ) reproduces the dependence of T_N on the

EuCu2Ge2 based on the results of the set of experi-

concentration of Si () presented in the inset. This means

ments (experiment titles correspond to the designations

that for EuCu₂Ge₂ system the effects of the hydrostatic

adopted in the text). Inset: magnetic phase diagram of

and chemical (substitution of Ge for Si) pressure on Eu-

EuCu2(SixGe1-x)2 based on the data from: heat capacity

valence are equivalent from the point of view of the tran-

and resistivity measurements [1] - down triangles, [2] -

sition to the antiferromagnetic ordered ground state.

stars, [3] - hexagons, magnetic neutron diffraction

The identity of the dependences of T_N on both x and

P proves that a homogeneous IV regime is realized in

the EuCu₂(Si,Ge)₂ system similarly to EuCu₂Ge₂ un-

is an indication that it develops on the basis of com-

der pressure, and the coexistence of the homogeneous

petition of the two magnetic configurations of Eu, one

IV and long range magnetic order for the RE sublattice

of which is formed on the base of initially nonmagnetic

is confirmed.

Eu³⁺ state. Therefore, some analogy can be suggested

The magnetic phase diagram is presented as a func-

for coexistence of magnetic order and homogeneous in-

tion of Eu average valence. The probable background for

termediate valence with the case of TmSe [5, 6] interme-

the formation of the magnetically ordered intermediate

diate valence system.

valence state of Eu is considered basing on the analysis

This is an excerpt of the article “Evidence of ho-

of the original neutron magnetic spectroscopy [4] data

mogeneous intermediate valence coexisting with long-

for f-electron excitations in the EuCu₂(Si,Ge)₂. There

range magnetic order in EuCu₂(Si,Ge)₂”. Full text

of the paper is published in JETP Letters journal.

¹⁾e-mail: savch92@gmail.com

DOI: 10.1134/S0021364021210049

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