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Description
A theoretical study of a three-dimensional (3D) N/S interface with arbitrary spin
polarization and interface geometry is presented. The 3D model gives the same intrinsic
spin polarization and superconducting gap dependence as the 1D model. This
demonstrates that the 1D model can be use to t 3D data.
Using this model, a Heusler alloy is investigated. Andreev reflection measurements
show that the spin polarization is 80% in samples sputtered on unheated MgO(100)
substrates and annealed at high temperatures. However, the spin polarization is
considerably smaller in samples deposited on heated substrates.
Ferromagnetic FexSix alloys have been proposed as potential spin injectors into
silicon with a substantial spin polarization. Andreev Reflection Spectroscopy (ARS) is
utilized to determine the spin polarization of both amorphous and crystalline Fe65Si35
alloys. The amorphous phase has a significantly higher spin polarization than that of
the crystalline phase.
In this thesis, (1111) Fe SmO0:82F0:18FeAs and Pb superconductors are used to
measure the spin polarization of a highly spin-polarized material, La0:67Sr0:33MnO3.
Both materials yield the same intrinsic spin polarization, therefore, Fe-superconductors
can be used in ARS. Based on the behavior of the differential conductance for highly
spin polarized LSMO and small polarization of Au, it can be concluded that the Fe-Sc
is not a triplet superconductor.
Zero bias anomaly (ZBA), in point contact Andreev reflection (PCAR), has been
utilized as a characteristic feature to reveal many novel physics. Complexities at a
normal metal/superconducting interface often cause nonessential ZBA-like features,
which may be mistaken as ZBA. In this work, it is shown that an extrinsic ZBA,
which is due to the contact resistance, cannot be suppressed by a highly spin-polarized
current while a nonessential ZBA cannot be affected the contact resistance.
Finally, Cu/Cu multilayer GMR structures were fabricated and the GMR% measured
at 300 K and 4.5 K gave responses of 63% and 115% respectively. Not only
do the GMR structures have a large enhancement of resistance, but by applying an
external magnetic eld it is shown that, unlike most materials, the spin polarization
can be tuned to values of 0.386 to 0.415 from H = 0 kOe to H = 15 kOe.
polarization and interface geometry is presented. The 3D model gives the same intrinsic
spin polarization and superconducting gap dependence as the 1D model. This
demonstrates that the 1D model can be use to t 3D data.
Using this model, a Heusler alloy is investigated. Andreev reflection measurements
show that the spin polarization is 80% in samples sputtered on unheated MgO(100)
substrates and annealed at high temperatures. However, the spin polarization is
considerably smaller in samples deposited on heated substrates.
Ferromagnetic FexSix alloys have been proposed as potential spin injectors into
silicon with a substantial spin polarization. Andreev Reflection Spectroscopy (ARS) is
utilized to determine the spin polarization of both amorphous and crystalline Fe65Si35
alloys. The amorphous phase has a significantly higher spin polarization than that of
the crystalline phase.
In this thesis, (1111) Fe SmO0:82F0:18FeAs and Pb superconductors are used to
measure the spin polarization of a highly spin-polarized material, La0:67Sr0:33MnO3.
Both materials yield the same intrinsic spin polarization, therefore, Fe-superconductors
can be used in ARS. Based on the behavior of the differential conductance for highly
spin polarized LSMO and small polarization of Au, it can be concluded that the Fe-Sc
is not a triplet superconductor.
Zero bias anomaly (ZBA), in point contact Andreev reflection (PCAR), has been
utilized as a characteristic feature to reveal many novel physics. Complexities at a
normal metal/superconducting interface often cause nonessential ZBA-like features,
which may be mistaken as ZBA. In this work, it is shown that an extrinsic ZBA,
which is due to the contact resistance, cannot be suppressed by a highly spin-polarized
current while a nonessential ZBA cannot be affected the contact resistance.
Finally, Cu/Cu multilayer GMR structures were fabricated and the GMR% measured
at 300 K and 4.5 K gave responses of 63% and 115% respectively. Not only
do the GMR structures have a large enhancement of resistance, but by applying an
external magnetic eld it is shown that, unlike most materials, the spin polarization
can be tuned to values of 0.386 to 0.415 from H = 0 kOe to H = 15 kOe.
ContributorsGifford, Jessica Anna (Author) / Chen, Tingyong (Thesis advisor) / Bennett, Peter (Committee member) / Nemanich, Robert (Committee member) / Tsen, Kong-Thon (Committee member) / Arizona State University (Publisher)
Created2015
Description
This dissertation features a compilation of studies concerning the biophysics of multicellular systems. I explore eukaryotic systems across length scales of the cell cytoskeleton to macroscopic scales of tissues. I begin with a general overview of the natural phenomena of life and a philosophy of investigating developmental systems in biology. The topics covered throughout this dissertation require a background in eukaryotic cell physiology, viscoelasticity, and processes of embryonic tissue morphogenesis. Following a brief background on these topics, I present an overview of the Subcellular Element Model (ScEM). This is a modeling framework which allows one to compute the dynamics of large numbers of three-dimensional deformable cells in multi-cellular systems. A primary focus of the work presented here is implementing cellular function within the framework of this model to produce biologically meaningful phenotypes. In this way, it is hoped that this modeling may inform biological understanding of the underlying mechanisms which manifest into a given cell or tissue scale phenomenon. Thus, all theoretical investigations presented here are motivated by and compared to experimental observations. With the ScEM modeling framework I first explore the passive properties of viscoelastic networks. Then as a direct extension of this work, I consider the active properties of cells, which result in biological behavior and the emergence of non-trivial biological phenotypes in cells and tissues. I then explore the possible role of chemotaxis as a mechanism of orchestrating large scale tissue morphogenesis in the early embryonic stages of amniotes. Finally I discuss the cross-sectional topology of proliferating epithelial tissues. I show how the Subcellular Element Model (ScEM) is a phenomenological model of finite elements whose interactions can be calibrated to describe the viscoelastic properties of biological materials. I further show that implementing mechanisms of cytoskeletal remodeling yields cellular and tissue phenotypes that are more and more biologically realistic. Particularly I show that structural remodeling of the cell cytoskeleton is crucial for large scale cell deformations. I provide supporting evidence that a chemotactic dipole mechanism is able to orchestrate the type of large scale collective cell movement observed in the chick epiblast during gastrulation and primitive streak formation. Finally, I show that cell neighbor histograms provide a potentially unique signature measurement of tissue topology; such measurements may find use in identifying cellular level phenotypes from a single snapshot micrograph.
ContributorsSandersius, Sebastian Ambrose (Author) / Newman, Timothy J (Thesis advisor) / Rez, Peter (Committee member) / Ros, Robert (Committee member) / Sankey, Otto F. (Committee member) / Tsen, Kong-Thon (Committee member) / Arizona State University (Publisher)
Created2011