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Register a new userCharacterisation of Ferromagnetic Contacts to Carbon Nanotubes
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Added by
Andreas K. H\\\"uttel
Publication date
2009
fields
Physics
and research's language is
English
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We present an investigation of different thin-film evaporated ferromagnetic materials for their suitability as electrodes in individual single-wall and multi-wall carbon nanotube-based spin devices. Various electrode shapes made from permalloy (Ni_{81}Fe_{19}), the diluted ferromagnet PdFe, and PdFe/Fe bilayers are studied for both their micromagnetic properties and their contact formation to carbon nanotubes. Suitable devices are tested in low-temperature electron transport measurements, displaying the typical tunneling magnetoresistance of carbon nanotube pseudo spin valves.
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We present a fabrication scheme called fork stamping optimized for the dry transfer of individual pristine carbon nanotubes (CNTs) onto ferromagnetic contact electrodes fabricated by standard lithography. We demonstrate the detailed recipes for a residue-free device fabrication and in-situ current annealing on suspended CNT spin-valve devices with ferromagnetic Permalloy (Py) contacts and report preliminary transport characterization and magnetoresistance experiments at cryogenic temperatures. This scheme can directly be used to implement more complex device structures, including multiple gates or superconducting contacts.
We report on spin dependent transport measurements in carbon nanotubes based multi-terminal circuits. We observe a gate-controlled spin signal in non-local voltages and an anomalous conductance spin signal, which reveal that both the spin and the orbital phase can be conserved along carbon nanotubes with multiple ferromagnetic contacts. This paves the way for spintronics devices exploiting both these quantum mechanical degrees of freedom on the same footing.
This contribution reports on comparative studies on giant magnetoresistance (GMR) in carbon nanotubes (CNTs) and graphene nanoribbons of similar aspect ratios (i.e perimeter/length and width/length ratios, for the former and the latter, respectively). The problem is solved at zero temperature in the ballistic transport regime, by means of the Greens functions technique within the tight-binding model and with the so-called wide band approximation for electrodes. The GMR effect in graphene is comparable to that of CNTs, it depends strongly on the chirality and only slightly on the aspect ratio. It turns out that graphene, analogously to CNTs may be quite an interesting material for spintronic applications.
In this study, a model of a Schottky-barrier carbon nanotube field- effect transistor (CNT-FET), with ferromagnetic contacts, has been developed. The emphasis is put on analysis of current-voltage characteristics as well as shot (and thermal) noise. The method is based on the tight-binding model and the non- equilibrium Greens function technique. The calculations show that, at room temperature, the shot noise of the CNT FET is Poissonian in the sub-threshold region, whereas in elevated gate and drain/source voltage regions the Fano factor gets strongly reduced. Moreover, transport properties strongly depend on relative magnetization orientations in the source and drain contacts. In particular, one observes quite a large tunnel magnetoresistance, whose absolute value may exceed 50%.
We present theoretical study of shot noise in single wall metallic carbon nanotubes weakly coupled to either nonmagnetic or ferromagnetic leads. Using the real-time diagrammatic technique, we calculate the current, Fano factor and tunnel magnetoresistance in the sequential tunneling regime. It is shown that the differential conductance displays characteristic four-fold periodicity, indicating single-electron charging. Such a periodicity is also visible in tunnel magnetoresistance of the system as well as in the Fano factor. The present studies elucidate the impact of ferromagnetic (vs. nonmagnetic) contacts on the transport characteristics under consideration.
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