Study Onmagnetization And Resistivity Of Manganite Thin Films

In strong correlation complex system materials, there are very strong couplings among various physical properties. Kinds of material’s order structures, such as magnetism, charge and crystal structure are closelycoupled with each other. While one parameter is changing, the others will alter with it. Hence, we have more degrees of freedom to control material’s properties. The tuning and controlling among various physical properties are indispensable for material’s application in multifunctional devices.In spin, charge, lattice and orbital coupled complex manganite system, the competitionsof various quantum order result in striking macroscopic phenomena, for instance, colossal magnetoresistance, giant magnetoresistance, magnetocaloric effectand multiferroicity. Therefore, the complex manganite is becoming a research hotspot in the field of condensed matter physics, as well as a new breakthrough for micro-electronics and information industry. However, how the interaction among quantum orders influence system’s macroscopic properties is still not understood well. Although different quantum orders have different characteristic lengths, the discrepancy of order structure’s characteristic lengths can be gradually eliminated by material’s structural design and spacial dimension confinement. When the system approaches the characteristic length, the different quantum order parameters will be affected in maximum level, corresponding macroscopic properties will also alter more obviously. So, reducing material’s dimensionality and scale may enhance the coupling among various order parameters. Moreover, thin film not only often have strong coupling than bulk materials, but also are more beneficial to device’s high density integration. As thin film materials are always epitaxial grown on various substrates, the influence of substrates on thin film sample’s properties is a very important research project.Epitaxial strain is the primary one of which substrate induced various impact factors to thin film. The current is another important factorthat can affect on the materials’ properties. In this work, the effect of lattice strain on La5/8Ca3/8Mn O3 thin film,and the effect of current density on(La2/3Pr1/3)5/8Ca3/8Mn O3 film are systematically studied. Followings are main study contents in this work:1、Using different substrates. Tuning the strain of epitaxial thin film by using different lattice constant substrates is one significant method to investigate strain. This work also uses this method to study the influences of strain on the magnetic and electrical transport properties of epitaxial La5/8Ca3/8Mn O3 thin films. Epitaxial LCMO thin films are fabricated on(001) La Al O3(LAO),(001) Sr La Ga O4(SLGO),(110)Nd Ga O3(NGO),(001)(La,Sr)(Al,Ta)O3(LSAT)and(001) Sr Ti O3(STO) substratesrespectively, epitaxial strain’s effect on thin film’s magnetic, electrical transport and MR effect are observed.2、Growing La5/8Ca3/8Mn O3 epitaxial thin film of various thicknesses on Ba Ti O3 substrate. The propagation and influence on thin film’s various physical properties of epitaxial strain in different thickness films are studied. We can observe different strain propagation has different contribution to thin film’s magnetic moment and resistivity. We control the physical properties of epitaxial thin films throughagate voltage controlled BTO substrate.In the gate voltage changing process,we found a significant change in the resistivity of the epitaxial LCMO films.3、For more intuitively observing the influence of strain’s alteration on La5/8Ca3/8Mn O3 thin film’s magnetic and transport properties. This work uses electrical field induced different crystal orientations of BTO substrate to tune strain. Thereby, the fancy phenomena of La5/8Ca3/8Mn O3 thin film’s magnetic and transport properties in structure transitionprocess of bothcrystal orientations BTOhave been observed.4、We measured the resistivity of(La2/3Pr1/3)5/8Ca3/8Mn O3 film under different current densities, and find the current density hasa huge effect on the resistivity. We unveiled the mechanism of the CER effect through measuring the macroscopic magnetic property and microcosmicmagnetic domain structure under different currentdensities.