  We report a bulk magnetisation study of the low temperature magnetic phases
in the Mn site substituted half doped manganite series
Pr_(0.5)Ca_(0.5)Mn_(1-x)Al_(x)O_(3). Our results indicate the formation of self
organised structures in this series of compounds which is driven by electronic
phase separation and stabilised by the presence of finite quenched disorder,
thus providing a basis for understanding the anomalously large supression of
the CE phase in the presence of disorder. Striking magnetic memory effects
similar to that seen in spin glasses and interacting superparamagnets are also
observed. Increasing disorder is seen to make electronic phase separation
weaker owing to the destabilisation of the CE state which results in an
enhanced mobility of the charge carriers.
