dc.contributor.advisor | Çıracı, Salim | |
dc.contributor.author | Can, Duygu | |
dc.date.accessioned | 2016-01-08T18:11:32Z | |
dc.date.available | 2016-01-08T18:11:32Z | |
dc.date.issued | 2009 | |
dc.identifier.uri | http://hdl.handle.net/11693/14959 | |
dc.description | Ankara : The Department of Physics and the Institute of Engineering and Science of Bilkent University, 2009. | en_US |
dc.description | Thesis (Master's) -- Bilkent University, 2009. | en_US |
dc.description | Includes bibliographical references leaves 50-54. | en_US |
dc.description.abstract | With 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.statementofresponsibility | Can, Duygu | en_US |
dc.format.extent | xiv, 54 leaves, illustrations | en_US |
dc.language.iso | English | en_US |
dc.rights | info:eu-repo/semantics/openAccess | en_US |
dc.subject | molecular electronics | en_US |
dc.subject | ballistic conductance | en_US |
dc.subject | transition metal atom | en_US |
dc.subject | carbon linear chain | en_US |
dc.subject | quantum transport | en_US |
dc.subject | spintronics | en_US |
dc.subject.lcc | TK7874.887 .C45 2009 | en_US |
dc.subject.lcsh | Spintronics. | en_US |
dc.subject.lcsh | Carbon. | en_US |
dc.subject.lcsh | Molecular electronics. | en_US |
dc.title | Bias voltage control of a molecular spin valve | en_US |
dc.type | Thesis | en_US |
dc.department | Department of Physics | en_US |
dc.publisher | Bilkent University | en_US |
dc.description.degree | M.S. | en_US |