  Measurements of magnetic hysteresis loops in Cu-Al-Mn alloys of different Mn
content at low temperatures are presented. The loops are smooth and continuous
above a certain temperature, but exhibit a magnetization discontinuity below
that temperature. Scaling analysis suggest that this system displays a disorder
induced phase transition line. Measurements allow to determine the critical
exponents $\beta=0.03\pm 0.01$ and $\beta \delta = 0.4 \pm 0.1$ in agreement
with those reported recently [Berger et al., Phys. Rev. Lett. {\bf 85}, 4176
(2000)]
