  We report muon spin rotation and magnetization measurements on the magnetic
superconductor RbEuFe$_{4}$As$_{4}$ under hydrostatic pressures up to 3.8 GPa.
At ambient pressure, RbEuFe$_{4}$As$_{4}$ exhibits a superconducting transition
at $T_{c} \approx$ 36.5 K and a magnetic transition at $T_{m} \approx$ 15 K
below which the magnetic and the superconducting order coexist. With increasing
pressure, $T_{c}$ decreases while $T_{m}$ and the ordered Eu magnetic moment
increase. In contrast to iron-based superconductors with ordering Fe moments,
the size of the ordered Eu moment is not proportional to $T_{m}$. The muon spin
rotation signal is dominated by the magnetic response impeding the
determination of the superconducting properties.

Superconductivity