Structural, Magnetic And Surface Properties Of RF Magnetron Sputtered Undoped Lanthanum Mangnite Thin Films
Sakhalkar, Varad Rajan
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In the present study, polycrystalline and epitaxial undoped Lanthanum Manganite (LMO) thin films were deposited by using RF magnetron sputtering on three substrates, Si (100), MgO (100) and LaAlO₃ (100) to study the influence of the misfit strain at the substrate/film interface. The effect of processing conditions on the synthesis of LMO films was studied by conducting deposition on Si wafer. Films were characterized by X-Ray Diffraction (XRD), Atomic Force Microscope (AFM), Energy Dispersive Spectroscopy (EDS) and Superconducting Quantum Interference Device (SQUID) to investigate the influence of processing parameters on their structure and properties. Based on the initial study on Si wafer, processing parameters were selected to deposit LMO thin films on MgO and LaAlO₃ substrates. The films were subsequently characterized using XRD, AFM, EDS and SQUID to study the structural, magnetic and surface properties of the as-deposited films as a function of substrate material. Selected films samples were heated at 800°C in oxygen atmosphere to determine effect of annealing on film microstructure. XRD results show that the as-deposited films at substrate temperature 750°C exhibited a good quality crystalline structure. On the contrary, the films deposited at 700°C exhibited a rather amorphous like structure. It was also found that the decrease in applied RF power led to better film crystallinity. XRD analysis also revealed that the films deposited on silicon wafer (bare and etched) exhibited a polycrystalline structure and whereas those deposited on LaAlO₃ and MgO had a good quality epitaxy. The annealing experiments revealed that the deficiency of oxygen in the as-deposited films was filled by heating at 800°C. AFM results revealed the formation of smooth surface and homogeneous films. SQUID studies showed that the magnetic moment of the films increased with decrease in temperature, below the Neel Temperature. Also, it indicated that the epitaxial films had higher phase transition temperature than the polycrystalline ones. The magnetic phase transition in epitaxial film was found to be 160K, better than reported in previous research. Thus, high quality epitaxial LMO films can be synthesized by RF magnetron sputtering that provides a process for large area deposition.