Magnetoresistive properties of thin nanostructured manganite films grown by metalorganic chemical vapour deposition onto glass-ceramics substrates

Abstract

The results of fabrication of nanostructured La_1−xSr _x MnO₃ films grown by pulsed injection metalorganic chemical vapour deposition technique onto special disordered glass-ceramics substrate are presented. Two groups of films were produced in order to determine what would be their main physical properties when certain fabrication changes were introduced: (1) films with thicknesses in the range of 25–900 nm, which were grown at a temperature of 750 °C; and (2) films having thicknesses of 400 nm, which were grown at different deposition temperatures ranging from 600 °C up to 775 °C in steps of 25 °C. It was determined that the morphology and microstructure of the films depends on the thicknesses of these films and their deposition temperatures. The thinnest films (25 nm) grew mainly in amorphous phase, while the thicker films had well-pronounced structure made of column-shaped crystallites. These had average column widths of 40–65 nm, were spread throughout the whole thickness of the films, and were separated by 5–10-nm-thick grain boundaries. The influence of growth conditions on the colossal magnetoresistance effect in these films was studied in pulsed magnetic fields of up to 20 T. The dependences of the magnetoresistance on the magnetic flux density were analysed using modified Mott’s hopping model. It was demonstrated that these nanostructured films behave as superparamagnetic materials with reduced magnetic properties due to disordered grain boundaries. The obtained results allow the tuning of the resistivity, magnetoresistance and the anisotropy of La_1−xSr _x MnO₃ manganite films, which were deposited onto glass-ceramic substrates, and thus to use them for the fabrication of high pulsed magnetic field sensors.