| There are strong interactions among charge，orbital，spin and lattice existing inperovskite-type manganite. Those multiple competition mechanisms lead to a seriesof physical phenomenon which can be used as a basis for developing spintronicdevices. Simultaneously, perovskite-type manganite is a “Natural Laboratory” forcondensed matter research，and be considered a precious gift given by natural worldto mankind. This thesis is targeted on La1-x-yCaxKyMnO3（LCKMO）, which co-dopedby monovalent potassium and bivalent calcium in A-site. Many novel properties suchas atomic-scale p-n junction, which is caused by complicated electronic statedistribution of Mnn+, were present in this compound. Here, we reported thepreparation of low dimensional LCKMO materials and their electromagnetic behavior,and the major results are as follows: a) LCKMO materials with four different kinds ofdimensions were prepared. Single crystal, film, nanotube and nanodot were preparedby hydrothermal synthesis and pulsed laser deposition method. b) The electronicproperties of single crystal and film were measured by several means, all the resultsreveal the rectify effect existing in LCKMO. c) The excellent MCE performance,which may cause by K ions substituted and strain effect in the LCKMO film, revealsits great applicative potentialities as magnetic cooling refrigerant. The main contentsfor each section in this dissertation are presented as follows: In chapter1, we introduce the research background and related basic theories ofperovskite-type manganit. A brief sketch of the rising spintronics andmanganite-based devices and its applications were given, and the choice item andbasic thought of this thesis are stated at last.In chapter2, we studied the electrical properties of LCKMO single crystals usingseveral kinds of experimental method such as two electrodes, variable temperatureatomic force microscope, focused ion beam assisted four electrodes and alternatingcurrent spectrometry. The perceptible rectify effects are consistently shown in singlecrystal test. When the crystal is forward biased, the current abruptly increase at thethreshold voltage, and the crystal cut off with the reverse bias applied.In chapter3, LCKMO films are prepared by pulsed laser deposition （PLD）method and then characterized systematically. The formation of laser-induced plasmaand kinetic process of the film growth are briefly introduced at the beginning, and usethem as the basis for optimization the growth conditions of the film purposefully. ICP,XRD, SEM, TEM, XPS and RBS are used to analyzing the resultant film, and theresults indicate that the LCKMO films with high crystalline quality were obtained onSrTiO3（STO） single crystal substrate.In chapter4, the electromagnetic properties of the LCKMO film were studied.The in plane transport properties was studied using four wire method, and the out ofplane was measured by atomic force microscope using a SrRuO3film as bottomelectrode. The expected rectify effect was observed and its mechanism was discussed.With the magnetic field change of5T, the maximum magnetic entropy change andrelative cooling power of the film is3.45J·kg-1·K-1and379.5J·kg-1, respectively. Anotable case is that the full width at half maximum of|ΔSM|is110K, which isdesirable for the Ericsson cycle. The excellent MCE performance of the LCKMO filmreveals its great applicative potentialities as magnetic cooling refrigerant.In chapter5, Low dimensional materials of perovskite-type manganite nanotubeand nanodot were prepared by template assisted pulsed laser deposition. After thedeposition on anodic aluminum oxide （AAO） nanopore membrane, we obtained the nanotube by removing the template in alkaline condition. The structure、morphologyand magnetic properties are characterized and the formation mechanism of the NTs isalso proposed. When we transfer the ultrathin AAO template to STO and then executePLD deposition，nanodot structure formed on STO substrate corresponding to the poredistribution. Further research is required to fully understand their performanceinduced by scale shrinking.In chapter6, a brief summary based on the full text was present, and the futureresearch and applications of atomic p-n junction were look forward.With the development of science and technology and the progress of society，humankind are understanding and transforming the objective world in nano-scalegradually， individual atoms and molecules were manipulated to produce newmaterials and new properties. Based on the experimental results, our group proposedthe idea of atomic scale p-n junction firstly. We provided ingredient and designthinking for new generation electronic information materials and devices architecture.In this thesis, diverse forms of LCKMO were developed, the existing of junctioneffect was verified by using multiple means, and its magnetocaloric effect was alsostudies. Those works lays a good foundation for the preparation of spintronics devicewith complex functions. |
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