Scanning probe microscopy investigation of bilayered manganites

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dc.contributor.advisorde Lozanne, Alejandro Len
dc.creatorHuang, Junwei, 1975-en
dc.date.accessioned2008-08-28T23:36:52Zen
dc.date.accessioned2017-05-11T22:18:03Z
dc.date.available2008-08-28T23:36:52Zen
dc.date.available2017-05-11T22:18:03Z
dc.date.issued2007en
dc.descriptiontexten
dc.description.abstractThe bilayered manganite La2−2xSr1+2xMn2O7, with x in the ferromagnetic compositional region, exhibits very interesting electronic and magnetic properties below the Curie temperature, such as a colossal magneto-resistance (CMR) effect. We have studied the microscopic electronic structure in the x = 0.32, 0.4 compounds at 80 K and 20 K by using a home-built low temperature scanning tunneling microscope (STM) and the evolution of the ferromagnetic domains with temperature and magnetic field in the x = 0.32 compound from 30 K to 110 K by using a home-built low temperature magnetic force microscope (MFM). STM topographic images show nano-sized patterns composed of Mn3+- rich and Mn4+-rich regions in the mixed-valent matrix. Tunneling spectra I(V )& dI dV (V ) show a gap and a tunneling asymmetry of the LDOS as a function of the sample bias voltage. By using current-imaging tunneling spectroscopy (CITS), we obtained a series of tunneling conductance maps which show the coexistence of localized electrons and itinerant electrons in this system. In the x = 0.32 compound, we observed a modulation with a wave vector of 16 ˚A propagating along a-axis at 20K. This indicates the formation of a charge density wave as a result of Fermi surface nesting in this system. In MFM images, we observed that below 60 K, the ferromagnetic (FM) domains form stable treelike patterns and the domains are mainly oriented in the out-of-plane direction. As the temperature increases, the FM domains begin to experience a gradual change. This change becomes more and more rapid above 80 K. The FM domains change their magnetization from the out-of-plane direction to in-plane around 88 K. The in-plane FM domains completely disappear near TC . We also observed thermal hysteresis occurring in magnetic structures. We conclude that the formation of FM domains at low temperatures is determined by the energy associated with surface magnetic free poles and domain walls. At high temperatures, the two-dimensional ferromagnetic fluctuation in the basal plane may also play an important role in forming the domain structures.
dc.description.departmentPhysicsen
dc.format.mediumelectronicen
dc.identifierb68890266en
dc.identifier.oclc174116475en
dc.identifier.urihttp://hdl.handle.net/2152/3253en
dc.language.isoengen
dc.rightsCopyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.en
dc.subject.lcshManganite--Electric propertiesen
dc.subject.lcshManganite--Magnetic propertiesen
dc.subject.lcshScanning tunneling microscopyen
dc.titleScanning probe microscopy investigation of bilayered manganitesen
dc.type.genreThesisen

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