Calorimetric study on EuCoGe₃ and EuRh₂In₈ under pressure

Abstract

We report here the phase diagrams of EuCoGe₃ and EuRh₂In₈ studied by ac calorimetry under pressure using a diamond anvil cell. EuCoGe₃ exhibits two antiferromagnetic transitions at T_N = 15 K and T’_N=13.4 K. With increasing pressure T_N and T’_N increase and the antiferromagnetic orders persist up to high pressure. A semi quantitative analysis of the pressure dependence of the specific heat does not show any large changes, but is compatible with a moderate enhancement of the effective mass for EuCoGe₃. The antiferromagnetic transition temperature T_N for EuRh₂In₈ initially increases slightly up to 8.7 GPa, and then increases abruptly between 8.7-11.9 GPa, the sudden increase in T_N in this pressure range may be due to a change in the magnetic structure with pressure. Further T_N increases linearly above 11.9 GPa up to high pressure. No sign of the expected valence transition is seen for either compound implying that this may only occur at rather high pressure for these systems.