0000000000070008
AUTHOR
Rui Wu
Methods for space-time parameter estimation in DS-CDMA arrays
Rui Wu tutki väitöstyössään radiokanavan eri ominaisuuksien arviointia. Tietämys radiokanavan ominaisuuksista on monesti välttämätöntä, jotta radiovastaanottimen vastaanottama signaali voidaan purkaa ymmärrettävään muotoon. Wu tutki hajaspektrijärjestelmiä, joissa esimerkiksi puhe- tai datasignaalin kaistanleveys moninkertaistetaan radiolähettimessä. Näin tehdään muun muassa jo toiminnassa olevissa 3G-puhelimissa ja -tukiasemissa. Kaistanleveyden moninkertaistamisella pyritään satunnaistamaan muille järjestelmän käyttäjille aiheutetut häiriösignaalit, koska kyseisissä järjestelmissä signaalit etenevät samalla taajuuskaistalla yhtäaikaisesti. Se, miten kunkin järjestelmän käyttäjän signaali …
Identifying the origin of the nonmonotonic thickness dependence of spin-orbit torque and interfacial Dzyaloshinskii-Moriya interaction in a ferrimagnetic insulator heterostructure
Electrical manipulation of magnetism via spin-orbit torques (SOTs) promises efficient spintronic devices. In systems comprising magnetic insulators and heavy metals, SOTs have started to be investigated only recently, especially in systems with interfacial Dzyaloshinskii-Moriya interaction (iDMI). Here, we quantitatively study the SOT efficiency and iDMI in a series of gadolinium gallium garnet (GGG) / thulium iron garnet (TmIG) / platinum (Pt) heterostructures with varying TmIG and Pt thicknesses. We find that the non-monotonic SOT efficiency as a function of the magnetic layer thickness is not consistent with the 1/thickness dependence expected from a simple interfacial SOT mechanism. Mor…
Magnetic Coupling in Y3Fe5O12/Gd3Fe5O12 Heterostructures
Ferrimagnetic ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (YIG) is the prototypical material for studying magnonic properties due to its exceptionally low damping. By substituting the yttrium with rare earth elements that have a net magnetic moment, we can introduce an additional spin degree of freedom. Here, we study the magnetic coupling in epitaxial ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$/${\mathrm{Gd}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (YIG/GIG) heterostructures grown by pulsed laser deposition. From bulk sensitive magnetometry and surface sensitive spin Seebeck effect and spin Hall magnetoresistance measurements, we determine the alignment of the heterostruct…
Revealing the Electronic Structure and Optical Properties of CuFeO2 as a p-Type Oxide Semiconductor
Delafossite CuFeO2 is a p-type oxide semiconductor with a band gap of ∼1.5 eV, which has attracted great interests for applications in solar energy harvesting and oxide electronics. However, there are still some discrepancies in the literature regarding its fundamental electronic structure and transport properties. In this paper, we use a synergistic combination of resonant photoemission spectroscopy and X-ray absorption spectroscopy to directly study the electronic structure of well-defined CuFeO2 epitaxial thin films. Our detailed study reveals that CuFeO2 has an indirect and d-d forbidden band gap of 1.5 eV. The top of the valence band (VB) of CuFeO2 mainly consists of occupied Fe 3d sta…