Preparation, Property, And Application Of Ferroic Thin Films

Due to their colossal magnetoresistance (CMR) effect et al, perovskite manganite films have attracted much attention for their potential application in high density memory, magnetic random access memory and spin-polarized all-oxides devices. Perovskite manganites, is a strongly correlated system, show intriguing physical phenomena such as charge order, orbital order and phase separation, and becomes one of main topics in condensed matter physics due to interplay of the charge, crystal lattice, spin and orbits et al. Hence, the investigation in CMR films has great significance for both spintronics fundamental physics research and all oxides or oxides-metal devices.Ferroelectric thin films have attracted great attention on various microelectronic devices such as nonvolatile ferroelectric random access memories and ferroelectric field-effect transistors due to their ferroelectric and piezoelectric property. Nonvolatile ferroelectric random access memory is a perfect memory device because the data could not lose when electricity is off. The imprint behavior and fatigue are both the factors abbreviating the lifetime of ferroelectric memory devices. It is significant to understand the imprint behavior and fatigue, and to overcome them.Multiferroic is a material that simultaneously possesses two or more of the so-called'ferroic'order parameters such as ferroelectricity, ferromagnetism, and ferroelasticity, which is most attracted attention on the material possessing ferroelectricity and ferromagnetism. Due to magnetoelectric coupling, multiferroics have the potential application in microelectronic devices such as magnetoelectric random access memories.In this thesis, we investigated the influence of the strain and thickness of perovskite manganites films on both magnetic and transport properties, charge ordering insulating state induced by the strain, and phase separation. We investigated the imprint behavior and fatigue of the Pt/PZT80/LSMO capacitors deposited by PLD. Based on above, we investigated magnetoelectric coupling of multiferroic films. The whole thesis consists of six chapters.Chapter 1: This is made of three parts. First, we review the physical properties of manganites including crystal structure, splitting of crystal field, ordering phases and phase separation, and effect of the strain and thickness on crystal structure and physical properties of manganites films. Second, we introduce the properties and application of ferroelectric films, including memories, crystal structure, domains polarization switching, and invalidation mechanism. Third, we introduce the multiferroic and magnetoelectric random access memories.Chapter 2: The film preparation method and samples measurement are introduced. Especially, the pulsed laser deposition (PLD) method and the preparation of ferroelectric memories and manganite films are described in details. Chapter 3: We introduce transport and magnetic properties of(La0.8Pr0.2)0.67Ca0.33MnO3 thin films grown on the substrates including LSAT(001), NGO(001), and NGO(110). Especially, we observed two phases coexistence induced by in-plane shear strain relaxation and a huge low-field magnetoresistance in a broad temperature range of 10-200 K for LPCMO/LSAT(001) thin films.Chapter 4: We investigate the effect of Pr doping on transport properties for La0.67Ca0.33MnO3 thin films. Due to the interplay of Jahn-Teller distortions and strain, the transport properties of the films are different from that of bulk.Chapter 5: We investigated the imprint behavior and fatigue of the Pt/PZT80/LSMO capacitors by PLD. We observed fatigue of the PZT80 films with LSMO electrodes, which is correlated with frequency. We study the imprint behavior of Pt/PZT80/LSMO capacitors, which is opposite to other author's observation.Chapter 6: We investigated magnetoelectric coupling of multiferroic films.