  Substitutions in the Mn-sublattice of antiferromagnetic, charge and orbitally
ordered manganites was recently found to produce intriguing metamagnetic
transitions, consisting of a succession of sharp magnetization steps separated
by plateaus. The compounds exhibiting such features can be divided in two
categories, depending on whether they are sensitive to thermal cycling effects
or not. One compound of each category has been considered in the present study.
The paper reports on the influence of two treatments: high-temperature
annealing and grinding. It is shown that both of these treatments can
drastically affect the phenomenon of magnetization steps. These results provide
us with new information about the origin of these jumps in magnetization.
