Effect of aluminium for manganese substitution upon the GMR properties of the praseodymium manganites

The substitution of Al for Mn in the GMR perovskites Pr0.7Ca0.2Sr0.1MnO3, Pr0.7Ca0.1Sr0.2MnO3 and Pr0.5Sr0.5MnO3 has been studied. For the first two series of compounds that belong to the type I GMR manganites [ferromagnetic (FM)-paramagnetic (PM) transition] T-C decreases significantly as the aluminium content increases, by about 12 K per percent of Al atoms introduced into the Mn sites, whereas the maximum magnetoresistance ratio R(O)/H-H is not modified dramatically, reaching 10(3) at 71 K for 6% Al per Mn in a magnetic field of 7 T. This increase of R(O)/R(H) is, in fact, correlated to the decrease of T-C, i.e. to the increase of the semiconductive character of the samples. For the sei-ies Pr0.5Sr0.5Mn1-xAlxO3, which belongs to type II [antiferromagnetic (AFM)-FM-PM transitions]; an increase of T-N from the AFM to the FM state is observed by Al doping: T-N increases from 136 K for x=0 to 179 K for x=0.06. In contrast, T-C decreases as x increases.