Bias voltage control of a molecular spin valve

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buir.advisorÇıracı, Salim
dc.contributor.authorCan, Duygu
dc.date.accessioned2016-01-08T18:11:32Z
dc.date.available2016-01-08T18:11:32Z
dc.date.issued2009
dc.departmentDepartment of Physicsen_US
dc.descriptionAnkara : The Department of Physics and the Institute of Engineering and Science of Bilkent University, 2009.en_US
dc.descriptionThesis (Master's) -- Bilkent University, 2009.en_US
dc.descriptionIncludes bibliographical references leaves 50-54.en_US
dc.description.abstractWith the discovery of giant magneto resistance a new field called spintronics is emerged. Utilizing spin-degree of freedom of the electron as well as its charge, high-speed devices which consumes low energy can be designed. One of the main concerns of spintronics is creating spin polarized currents. Half-metallic materials, which conduct electrons of one spin state but behave as an insulator for the other spin state, are ideal candidates for this purpose. In a way they function as spinvalves, and the current passing through these materials will be spin polarized. The half-metallic property of periodic atomic chains of carbon-transition metal compounds and spin-valve property of transition metal caped finite carbon linear chains motivated our study. In this work, we analyzed the spin dependent transport properties of CrCnCr atomic chains. We connected the magnetic CrCnCr molecules to appropriate electrodes and studied their electronic and magnetic properties under applied bias. All the calculations are carried out using a method which combines density functional theory (DFT) with non-equilibrium Green’s function (NEGF) technique. For CrCnCr molecules with odd n we observed cumulenic bond lengths, while the C−C bonds are in polyynic nature for even n. In these structures Cr atoms induce net magnetic moments on C atoms. The magnetic moment on Cr atoms favors anti-parallel (AF) alignment for even n and parallel (FM) alignment for odd n. This situation is inverted when the molecules are connected to the electrodes. Two-probe conductance calculations of such systems reveal that their conductance properties are also n dependent. Finite bias voltages which create non-equilibrium conditions within the device region, causes the spin-degenerate molecular levels of the device to be separated from each other. Then conductance properties of the device become spin dependent. We observe that the ground state CrCnCr two-probe systems with odd n changes from AF to FM at a critical voltage. Thus, we have a spinvalve which is initially in ”off-state” turned on with applied bias. We achieved to control spin-polarization of the current transmitted through a molecular spinvalve with applied bias voltage. We showed that they are molecular analogues of GMR devices. These molecular spin-valve devices function without any need of an external magnetic field as it is required in conventional GMR devices.en_US
dc.description.degreeM.S.en_US
dc.description.provenanceMade available in DSpace on 2016-01-08T18:11:32Z (GMT). No. of bitstreams: 1 0003930.pdf: 1915907 bytes, checksum: dc49148f1d808d7facd8b333c06bede4 (MD5)en
dc.description.statementofresponsibilityCan, Duyguen_US
dc.format.extentxiv, 54 leaves, illustrationsen_US
dc.identifier.urihttp://hdl.handle.net/11693/14959
dc.language.isoEnglishen_US
dc.publisherBilkent Universityen_US
dc.rightsinfo:eu-repo/semantics/openAccessen_US
dc.subjectmolecular electronicsen_US
dc.subjectballistic conductanceen_US
dc.subjecttransition metal atomen_US
dc.subjectcarbon linear chainen_US
dc.subjectquantum transporten_US
dc.subjectspintronicsen_US
dc.subject.lccTK7874.887 .C45 2009en_US
dc.subject.lcshSpintronics.en_US
dc.subject.lcshCarbon.en_US
dc.subject.lcshMolecular electronics.en_US
dc.titleBias voltage control of a molecular spin valveen_US
dc.typeThesisen_US

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