Suppression of the ferromagnetic transition due to Y substitution in La_2/3Sr_1/3MnO3 thin films and Superlattices*

We have investigated the magnetic properties of thin films related to the standard CMR system La_2/3Sr_1/3MnO₃ where Y substituted for 50% of the La atoms. These La_1/3Y_1/3Sr_1/3MnO₃ films were grown as a random alloy where La, Y and Sr atoms randomly occupied the A-site or as a superlattice where each unit-cell-thick layer stacked along the crystallographic (001) direction contained only one of the atoms La, Y and Sr occupying the A-site. One of the key magnetic features of La_2/3Sr_1/3Mn0₃ is a prominent ferromagnetic transition near 350 K. We find the substitution of La with Y suppresses this ferromagnetic transition in both the random alloy and the superlattice samples. In the superlattice sample we find a magnetic transition that is coincident with a metal-to-insulator transition we observe in electronic transport. In the random alloy sample, we see a similar magnetic transition but at lower temperatures where we find the sample is too insulating to measure electronic transport. We will compare our measurements on these La_1/3Y_1/3Sr_1/3MnO₃ samples with CMR thin films of La_2/3Sr_1/3MnO₃.