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.
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