Spin-dependent electron transport in nanoscale samples

Electron transport;Spin;Nanoparticle;Spintronics

Wei, Yaguang ; Physics

University:Georgia Institute of Technology

Department:Physics

关键词: Electron transport;    Spin;    Nanoparticle;    Spintronics;   

Others  :  https://smartech.gatech.edu/bitstream/1853/26498/1/wei_yaguang_200712_phd.pdf

美国|英语

来源: SMARTech Repository

【 摘 要 】

In this thesis, we describe the research in which we use metallic nanoparticles to explorespin-dependent electron transport at nanometer scale. Nanoscale samples were fabricatedby 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 ofbias voltage and magnetic field at low temperatures (down to ∼ 30mK).At low temperatures, the discrete energy levels within a metallic nanoparticle provides anew means to study the physics of the spin-polarized electron tunneling. We describe measurementsof spin-polarized tunneling via discrete energy levels of single Aluminum grain.Spin polarized current saturates quickly as a function of bias voltage, which demonstratesthat the ground state and the lowest excited states carry spin polarized current. The ratioof electron-spin relaxation time (T1) to the electron-phonon relaxation rate is in quantitativeagreement with the Elliot-Yafet scaling, an evidence that spin-relaxation in Al grainsis driven by the spin-orbit interaction. The spin-relaxation time of the low-lying excitedstates is T1 ¡Ö 0.7 µs and 0.1 µs in two samples, showing that electron spin in a metallicgrain could be a potential candidate for quantum information research.We also present measurements of mesoscopic resistance fluctuations in cobalt nanoparticlesat low temperature and study how the fluctuations with bias voltage, bias fingerprints,respond to magnetization-reversal processes. Bias fingerprints rearrange when domains arenucleated or annihilated. The domain wall causes an electron wave function-phase shiftof ∼ 5 ¦Ð. The phase shift is not caused by the Aharonov-Bohm effect; we explain how itarises from the mistracking effect, where electron spins lag in orientation with respect tothe moments inside the domain wall. The dephasing length at low temperatures is only 30nm, which is attributed to the large magnetocrystalline anisotropy in Co.xi