Magnetic properties of La$_{2/3}$Sr$_{1/3}$MnO$_{3}$/Pr$_{2/3}$Ca$_{1/3}$MnO$_{3}$ superlattices

We present a magnetization study of ferromagnetic/antiferromagnetic (FM/AFM) manganite superlattices, grown by pulsed laser deposition on SrTiO$_{3}$ substrates. The FM layers are 15-nm-thick La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ (LSMO) sheets and the AFM layers were made of Pr$_{2/3}$Ca$_{1/3}$MnO$_{3}$ (PCMO), with variable thickness t$_{A}$ between 0 and 7.6 nm. Although all our multilayers exhibit a PM-FM transition of the LSMO layers at T$_{C}\sim $340K, only for t$_{A}$=0 do we observe a FM moment M$_{0}$ close to the expected saturation for the 1/3 doping. As soon as the AFM layers are added (t$_{A}$= 0.8nm) M$_{0}$ decreases, related to the introduction of the FM/AFM interfaces. The lack of exchange bias would indicate that the reduction of the FM moment is due to the appearance of a magnetically dead layer in the LSMO close to the interface with the AFM volume. Upon a further increase of t$_{A}$, the FM moment increases again and develops a peak at t$_{A}\sim $3.5 nm. We explain this behavior in terms of the accommodation of nanometric FM droplets in the PCMO layers.