Calorimetric Study on EuCoGe3 and EuRh2In8 under Pressure

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.