We performed magnetization measurements on the reentrant magnetic superconductor ErxY1-xRh1.1Sn3.6 (x = 0.8, 0.9, 1) using a SQUID magnetometer in a 3He-4 He dilution refrigerator. The temperature was varied between 50 mK and 2 K and different background fields were used. The experiments were concentrated on the behaviour of the magnetic flux within the samples. The flux is frozen at the superconducting transition temperature when the sample is cooled from the paramagnetic region and reaches the value for the ferromagnetic state when superconductivity is destroyed. The hysteretic behaviour of the flux with decreasing and increasing temperature gives information about the critical fields and currents of the compounds.