Bir moleküler spin süzgecinin öngerilim voltajı ile kontrolü

With the discovery of giant magneto resistance a new field called spintronicsis 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 mainconcerns of spintronics is creating spin polarized currents. Half-metallic materials,which conduct electrons of one spin state but behave as an insulator for the otherspin 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 metalcompounds and spin-valve property of transition metal caped finite carbon linearchains motivated our study. In this work, we analyzed the spin dependenttransport properties of CrCnCr atomic chains. We connected the magneticCrCnCr molecules to appropriate electrodes and studied their electronic andmagnetic properties under applied bias. All the calculations are carried out usinga method which combines density functional theory (DFT) with non-equilibriumGreen?s function (NEGF) technique. For CrCnCr molecules with odd n weobserved cumulenic bond lengths, while the C?C bonds are in polyynic naturefor even n. In these structures Cr atoms induce net magnetic moments on Catoms. The magnetic moment on Cr atoms favors anti-parallel (AF) alignmentfor even n and parallel (FM) alignment for odd n. This situation is invertedwhen the molecules are connected to the electrodes. Two-probe conductancecalculations of such systems reveal that their conductance properties are also ndependent. Finite bias voltages which create non-equilibrium conditions withinthe device region, causes the spin-degenerate molecular levels of the device to beseparated from each other. Then conductance properties of the device becomespin dependent. We observe that the ground state CrCnCr two-probe systemswith odd n changes from AF to FM at a critical voltage. Thus, we have a spinvalvewhich is initially in ?off-state? turned on with applied bias. We achievedto control spin-polarization of the current transmitted through a molecular spinvalvewith applied bias voltage. We showed that they are molecular analogues ofGMR devices. These molecular spin-valve devices function without any need ofan external magnetic field as it is required in conventional GMR devices.