In this thesis, we describe the research in which we use metallic nanoparticles to explore
spin-dependent electron transport at nanometer scale. Nanoscale samples were fabricated
by using a state of the art electron beam lithography and shadow evaporation technique.
We have investigated spin relaxation and decoherence in metallic grains as a function of
bias voltage and magnetic field at low temperatures (down to ∼ 30mK).
At low temperatures, the discrete energy levels within a metallic nanoparticle provides a
new means to study the physics of the spin-polarized electron tunneling. We describe measurements
of spin-polarized tunneling via discrete energy levels of single Aluminum grain.
Spin polarized current saturates quickly as a function of bias voltage, which demonstrates
that the ground state and the lowest excited states carry spin polarized current. The ratio
of electron-spin relaxation time (T1) to the electron-phonon relaxation rate is in quantitative
agreement with the Elliot-Yafet scaling, an evidence that spin-relaxation in Al grains
is driven by the spin-orbit interaction. The spin-relaxation time of the low-lying excited
states is T1 ¡Ö 0.7 µs and 0.1 µs in two samples, showing that electron spin in a metallic
grain could be a potential candidate for quantum information research.
We also present measurements of mesoscopic resistance fluctuations in cobalt nanoparticles
at low temperature and study how the fluctuations with bias voltage, bias fingerprints,
respond to magnetization-reversal processes. Bias fingerprints rearrange when domains are
nucleated or annihilated. The domain wall causes an electron wave function-phase shift
of ∼ 5 ¦Ð. The phase shift is not caused by the Aharonov-Bohm effect; we explain how it
arises from the mistracking effect, where electron spins lag in orientation with respect to
the moments inside the domain wall. The dephasing length at low temperatures is only 30
nm, which is attributed to the large magnetocrystalline anisotropy in Co.
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| Identifer | oai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/26498 |
| Date | 14 November 2007 |
| Creators | Wei, Yaguang |
| Publisher | Georgia Institute of Technology |
| Source Sets | Georgia Tech Electronic Thesis and Dissertation Archive |
| Detected Language | English |
| Type | Dissertation |
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