Magnetotransport Studies of Complex Oxide Based Thin Films, Nanostructures and Heterostructure

In this work, comprehensive magnetotransport studies have been carried out to examine the electronic and magnetic properties of ferroic perovskite oxide thin films, nanostructures and heterostructures. We employ planar Hall effect (PHE) to probe the in-plane magnetocrystalline anisotropy (MCA) of (La,Sr)MnO3 (LSMO) thin films. The observed biaxial MCA with the easy axis along agrees with reported values in literature. When the top layer of LSMO thin films is patterned into nanoscale periodic stripes, we observe emergent uniaxial MCA with the easy axis along one of the original biaxial easy axes. The anisotropy energy density within the nanostripes is 50-fold higher than that of unpatterned LSMO and comparable with the value for Co. This study provides new insights in controlling MCA in LSMO via nanostructure engineering and may facilitate its applications in spintronic devices due to enhanced thermal stability.;Ferroelectric field effect is used to evaluate the contribution of charge to the magnetic properties of LSMO thin films. The polarization field of Pb(Zr,Ti)O 3 (PZT) top gate is used to reversibly modulate the magnetic properties in LSMO thin films. PHE studies of PZT/LSMO heterostructures reveal an enhanced biaxial MCA with the increase of hole doping in LSMO, with the magnitude comparable with that of chemical doping. This study highlights how ferroelectric field effect can be used to independently probe the effects of charge, spin and orbital in MCA with implications in low-power oxide spintronic devices.;Graphene field effect sensors are used to sensitively probe the polarization-related properties of (Ba,Sr)TiO3 (BSTO) thin films. Hall effect measurements are used to extract the carrier density induced in graphene by ferroelectric BSTO gate. By studying the polarization induced carrier density modulation, we have characterized the pyroelectric, dielectric and ferroelectric properties of BSTO thin films. Quantum Hall effect studies of BSTO gated graphene highlight the polarization asymmetry of the ferroelectric oxide gate. We also study how the ferroelectric induced resistance hysteresis in graphene varies with temperature, which reveals the critical role of interface chemistry played in the performance of graphene-ferroelectric hybrid devices.