Giant magnetoresistive thin films of (La,Pr)0.7(Ca,Sr)0.3MnO3 prepared by aerosol MOCVD

Abstract

It has been demonstrated that high quality thin films of Ln _1-x M _x MnO ₃ can be successfully prepared by aerosol MOCVD at 750 °C from volatile thd complexes. Subsequent annealing in oxygen at 750 °C is necessary to stabilize the oxygen content of the films. XRD patterns of the films showed them to be pseudocubic with an apparent lattice parameter linear in the average ionic radius of Ln and M. The evolution of Ln _1-x M _x MnO ₃ film morphology with increasing the film thickness has also been studied. The morphological instability of the MOCVD process results in the formation of a hillocky surface with thickness >2000 Å. The electrical properties of La _1-x Ca _x MnO ₃ and La _1-x Sr _x MnO ₃ correlate with those reported for bulk and thin film materials. The substitution of Pr for La in La _1-x Sr _x MnO ₃ reduces the maximum resistivity temperature, T _p , non-linearly. La _1-x Ca _x MnO ₃ thin films reveal a shift of T _p downwards in the case of substrate materials with a positive lattice mismatch with the films. La _0.35 Pr _0.35 Ca _0.3 MnO ₃ /LaAlO ₃ demonstrates a very complex temperature dependence of the resistivity, which is described using a conceptual phase diagram of Ln _1-x M _x MnO ₃ . A marked GMR effect was observed for La _0.35 Pr _0.35 Ca _0.3 MnO ₃ /LaAlO ₃ below 21 K (ca. 10 ¹⁰ %) and at ca. 70 K even in a field of 1 T.