Manipulation Of Transport Properties In Electronic-phase-separated Manganite Under External Fields

Electronic phase separation(EPS)is usually observed in transitional metal oxide(TMO).It is the result of the coexistence and competing of phase structures which have similar energies.Many systems with correlated electrons,have been shown to contain inherent electronic inhomogeneity near a phase transition without segregation of chemical composition.Perovskite manganite is a typical system of EPS,in which ferromagnetic metallic(FMM)phase and charge-ordered insulating(COI)phase coexist at nanometer or sub-micrometer scale.Under some special conditions,such as spatial confinement,many fascinating emergent phenomena will be exhibited in this system.The research of its EPS behavior and related manipulation,is not only helpful to understand the basic physical problem,but can also contribute to the development of the future applications in spintronics.In this thesis,we investigate the manipulation of the transport and magnetic properties under external fields(include magnetic and electric field)in the well-known large-scale EPS system La1-x-yPryCaxMnO3(LPCMO).(1)Magnetically induced nonvolatile magnetoresistance and resistance memory effect in an electronic phase-separated manganiteAn electronic phase-separated manganite LPCMO(x=5/8,y=0.3)thin film was prepared on the SrTi03(100)substrate.In the hysteresis region of metal-to-insulator transition(MIT),the resistance exhibits a sharp drop with the application of magnetic field and maintains the low resistance state after the removal of field,showing nonvolatile magnetoresistance(MR).The high resistance state can be recovered till the temperature is warmed,exhibiting the resistance memory effect.More explicit measurements at hysteresis region exhibit the non-volatility and irreversibility of MR,which can be ascribed to the percolative feature in the electronic phase-separated manganite.Moreover,the MR effect is dependent to the relative direction among the measurement current,external magnetic field and sample plane.These results can provide useful information regarding the percolative feature in the EPS system and be potentially used in logic circuits and storage technology,opening an attractive way for application in novel electronic devices.(2)Nonvolatile control of transport and magnetic properties in a magnetoelectric heterostructure by electric fieldNonvolatile manipulation of properties in some special materials under external electric field is meaningful in information storage.The construction of multiferroic ferroelectric/ferromagnetic composites is an effective approach to manipulate the transport and magnetic properties by electric field.A multiferroic LPCMO/PMN-PT(011)heterostructure was prepared.In this heterostructure,the LPCMO film shows first-order metal-to-insulator transition(MIT),and its in-plane transport is anisotropic.When a relatively small electric field is applied at room temperature,the MIT temperature of LPCMO layer increases and the resistance in its thermal hysteresis region decreases as the effect of the remnant stain.Meanwhile,the magnetism of the sample is also enhanced.In other words,the nonvolatile manipulation induced by electric field of the transport and magnetic properties is achieved.This effect can be ascribed to the modulation of the percolative transport induced by the remnant strain,and may be helpful for the development of new storage devices with low power consumption.(3)Electric field induced nonvolatile manipulation of metal-to-insulator transition of an electronic-phase-separated manganite with resistive switching effectThe electrically induced resistive switching(RS)effect have attracted increasing attention for the promising application in next generation nonvolatile memories,i.e.,the resistance random access memory(RRAM).On the other hand,it is also worth noting that some physical properties of materials can be manipulated through RS effect.We prepared a Au/LaAl03(LAO)/LPCMO heterostructure on the SrTi03(100)substrate.A reversible and stable bipolar resistive switching effect is observed in this device at room temperature and an ON/OFF resistance ratio of about two orders of magnitude is shown.Once a part of RS cells setting,the resistance of the LPCMO layer increases and the metal-to-insulator transition(MIT)temperature decreases remarkably.After the resetting of these cells,the MIT temperature increases,but it is still lower than the initial state.Further analysis indicates that electric field induced migration at the two sides of LAO/LPCMO interface of oxygen vacancies and their segregation around the RS cells in LPCMO layer would be responsible for the changes of resistivity and MIT temperature.In this research,new RS devices and mechanisms as well as novel methods to control the transport properties of EPS manganite are explored,which may be considerable for the application in spintronics.