| In this work, an electrostatic field effect approach is presented to modulate magnetism and metallicity of the colossal magnetoresistive oxide La1-xSrxMnO 3 (LSMO), using the polarization field of a ferroelectric oxide, Pb(Zr,Ti)O 3 (PZT). In its ferromagnetic metallic phase, LSMO possesses nearly metallic carrier densities, with corresponding electronic screening lengths of ∼1 nm. The field effect happens exclusively at the interface of PZT and LSMO, which requires ultrathin films with high structural and surface quality to observe a substantial modulation. Using off axis radio frequency magnetron sputtering, we have fabricated epitaxial single crystal LSMO thin films, PZT thin films, and PZT/LSMO heterostructures on 001 SrTiO3 substrates using off axis radio frequency magnetron sputtering, with excellent crystallinity and surface properties having been achieved.; Using the polarization field of PZT, we have reversibly modulated the magnetic Curie temperature and magnetoresistance of the system. The electrostatic modulation of TC is also observed in Hall effect measurements. Within the temperature range between the Curie temperatures of the two states, one can turn on and off the magnetic ordering. In a heterostructure where the active layer is one atomic layer (∼2 A) thinner, insulating behavior has been observed over the entire temperature range by depleting the carriers, showing that we are working within the screening length of the system. This study also has implications for nanoscale devices, such as nonvolatile magnetic memories and Mott metal-insulator transition field effect transistors, providing a route to transcend the size scaling limits of mainstream semiconductor devices. Along this line, we have investigated some of the practical aspects of these devices, such as the on/off ratio, switching behavior, and stability. We have also studied the anistropic magnetoresistance (AMR), planar Hall effect, and giant planar Hall effect in LSMO. We have modulated the AMR in ultrathin manganite films using the field effect approach, where we have observed a striking difference between electric field doping and chemical doping results, deconvolving for the first time the effects of charge and chemical distortion/disorder on the fundamental properties, such as the magnetic anisotropy and spin-orbit coupling, in these materials. |
