The Kondo-Like Transport Properties Of Magnetic-Order System Characterization And Remote Control Of Magnetic Nano-Particles

The strongly correlated manganites with prevoskite structure has a strongcoupling between the spin, orbit, charge and lattice freedom of degree which lead to aseries of novel physical behaviors related to the basic conception and importantquestions in modern physics and materials science, such as strongly correlatedelectrons, metal-insulator （M-I） transition, ordering parameters, spintronics anddevices physics etc. Recent research is focused on the mechamism of the strongcorrelated manganites, especially the understanding of noval and conplicatedelectrical and magnetical transport especially at low temperature because of the strongcorrelated character. At low temperature the mainly influence of conduction electron,the effect of phonon is weaking which can reflet the intrinsic physical mechanism.Among these, the research in the low-temperature transport behavior is very important.It can discuss the mechamism of strong correlated system and can provide greatimportant information.This thesis focuses on the abnormal transport properties of CMR mananites atlow temperature. We synthesize a series of different policrystal, single crystal andfilm samples and study the low temperature transport properties, through fitting andsimulating separate each factor such as spin scattering, intrinsic inhomgenious, grainboundary and quantum tunneling, e-e interaction, localized effect andnano/micro-phase separation and so on. We discuss the different influence effectwith strong correlated character in order to give a detailed explanation for theabnormal low temperature transport properties and provide aboundant experimentsand basic data for the understanding of mechanism correlated system andcomplicated system.In Chapter One, we review the research on the low-temperature transport properties and the related theoretically models for CMR magnates. Then we introducethe abnormal low twmperature transport properties due to the intrinsic/extrinsicdefects and spin scattering exist in the strong correlated manganitesThe motivationand the proposal are presented in the end of this chapter.In Chapter Two, the main methods and principles in our experiment areintroduced, including the preparation of samples, structural properties analysis andphysical property including the electrical and magnetic measurement on the study ofCMR magnates.The third chapter gives a serious result of artificial defect La_2/3Sr_1/3MnO₃singlecrystal growed by floating zone method. Through control the atmosphere of Arcondition in order to bring the disorder into the magnatis single crystal. It gives thedirct evidence of low temperature abnormal properties correlated with spin disorderscattering by compared with a serious of defects and disorder in polycrystal and filmssamples. The results supposed that oxygen deficient environment should lead tointrinsic magnetic disorder in the spin system by affecting the oxygen-dependentexchange effect. We have observed the emergence of stripe-like phase arranged in theas-grown sample, which generated by the chemical fluctuation in the crystal as aresult of oxygen deficiency and vanished after anneling. There is a large diffenercebetween asgrown sample and annealing sample. The annealing sample show excellentproperties of La_2/3Sr_1/3MnO₃. The low temperature resistivity minimum in theannealing sample is diseapered which exists in the asgrown sample. Extrinsic grainboundry tunnealing and intrinsic magnetic scattering defects are the main reason forthe magnates. This work gives us a crucial way to understand the transport propertiesof intrinsic dishomogenous and extrisc gefects in manganites at low temperature.The fourth chapter is mainly about the study of the effects offerroelectric-poling-induced strain on Kondo-like electrical transport at lowtemperatures which have been investigated as a function of magnetic field forLa_0.7Ca_0.15Sr_0.15MnO₃thin films grown on ferroelectric0.67Pb(Mg_1/3Nb_2/3)O₃–0.33PbTiO₃（PMN-PT） single-crystal substrates. The ferroelectric poling in situ induceds an in-plane compressive strain effect. Whether the PMN-PT substrate is inunpoled or poled state, the temperature where the resistivity shows an upturn below20K shifts to a higher temperature under magnetic field. The ferroelectric polinginduces a reduction in the in-plane tensile strain and thus the lattice distortion of thefilm, which suppresses the resistivity upturn. These prove that the local latticedistortion relevant to the strain of the film is one of the main disorders that influencethe resistivity upturn. The results show that the low temperature resistivity upturn iscaused from quantum correction effects driven by electron-electron interaction andinelastic scattering.The fifths chapter studies the effects of Co substitution on Mn sites in thecolossal magnetoresistance （CMR） compound La2/3Ca1/3MnO₃have been studied bypreparing the series polycrystalline samples of La_2/3Ca_1/3Mn_1-xCo_xO₃（x=0⁰.15）. Acareful study in the structure, magnetoresistance （MR） effect, magnetic and electricaltransport properties has been carried out by the measurements of XRD,magnetization,resistivity, and magnetoresistance in this paper. Magnetic properties show the Curietemperature （TC） decreases and the PM-FM transition broadens gradually with theincreases of Co content which signifies the formation of cluster-glass state andmagnetic disorder in this system. The value of ZFC magnetization varies non-linearlyin the doped samples indicates the system is intrinsically inhomogeneous. For thewhole doing range（x=0⁰.15） there is an insulating-metallic （IM） transitionassociated with a paramagnetic-ferromagnetic transition. The magnitude of resistivityof the samples increases dramatically with the increasing of the Co doing content.Under the applied field the IM transition temperature TIMshifts to high temperatureand resistivity decreases over the whole temperature range for all samples. We alsofind all the resistivity curves of the compounds exhibit a slight low temperatureminimum around25K and this phenomenon become more abnormal with the dopingcontent increasing. The disorder in sample increases with the Co doping increases,and it leads to a competition with extrinsic defects and intrsic disorder. So it provesthe low temperature resisitivity minimum is the result of muti-effect. In Chapter six, we introduce the basic properties of magnetic nano-particles andthe application in biological environment. Then we introduce some detectmeasurement for magnetic nano-particle. According to simulation we made a newsetup of Electromagnetic Tweezers which used as a tool to remote control themovement of Magnetic Nanoparticles. The movement of magnetic nano-particles canbe record by a CCD camera, and then we can get the result of magnetic force actingon it. In order to achive the contrl of movement the electrical magnetic tweezersconnected to a3D manipulation platform. We also use the SQUIDmagnetorelaxometry to determine the binding state by evaluation of the differentBrownian and Neel relaxationtimes. At last of this chapter we list the challenges andproblems we met in this experiment.In Chapter seven，we summarize the present thesis and discusses the openquestions on the novel transport for strong correlated CMR mangnaties at lowtemperature.