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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2022)

The rise of neuromorphic computing and iteration of new memory call for energy-efficient magnetization manipulation by spin and a better understanding of fundamental magnetotransport properties. Over the past decades, most works on the spin source focused on polycrystalline and amorphous materials. In the first part of this dissertation, we investigate the spin Hall effect in epitaxial Pt (200), (220), and (111). A tunable spin current generation can be achieved in Pt (220). The charge-to-spin conversion efficiency can be significantly enhanced along specific crystallographic orientation by utilizing the anisotropic resistivity Our work highlights the future work on enhanced SHE arising from crystalline orientation dependence which will boost the energy-efficient spintronic devices.

On the other hand, tunable charge-to-spin conversion can be achieved by utilizing the materials with magnetic phase transition, which motivated us to study the 3d transition metal-Pt3 alloy and the rare earth material (Ho). Prior to further spintronics study, the fundamental magnetotransport properties in those materials need to be investigated. We successfully fabricate the chemically ordered epitaxial CrPt3 and FePt3. The large anomalous Hall effect measured on CrPt3 is in good agreement with the theoretical prediction. Moreover, by probing the exchange bias via electrical transport, it helps us quantitatively investigate the stability of antiferromagnetic nature in FePt3 under external perturbations.

Furthermore, there are still intriguing properties remaining in "old" materials which lead to the magnetotransport study on hcp Ho and hcp Co. Our discovery of six-fold angular dependent magnetoresistance and step-like planar Hall effect in Ho gives rise to the strong magnetostriction coupled magnetoresistance. Remarkably, although predicted years ago, the strong c-axis dependent anomalous Hall conductivity in hcp Co lacks experimental support, which is demonstrated in this dissertation. The magnetotransport study on hcp Co offers a comprehensive picture of anisotropic anomalous Hall effect and magnetoresistance in ferromagnets with in-plane uniaxial magnetic anisotropy.

    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2022)
    3D hosts are promising to extend the cycle life of lithium metal anodes but have rarely been implemented with lean electrolytes thus impacting the practical cell energy density. To overcome this challenge, a 3D host that is lightweight and easy to fabricate with optimum pore size that enables full utilization of its pore volume, essential for lean electrolyte operations, is reported. The host is fabricated by casting a VGCF (vapor-grown carbon fiber)-based slurry loaded with a sparingly soluble rubidium nitrate salt as an additive. The network of fibers generates uniform pores of ≈3 µm in diameter with a porosity of 80%, while the nitrate additive enhances lithiophilicity. This 3D host delivers an average coulombic efficiency of 99.36% at 1 mA cm-2 and 1 mAh cm-2 for over 860 cycles in half-cell tests. Full cells containing an anode with 1.35-fold excess lithium paired with LiNi0.8 Mn0.1 Co0.1 O2 (NMC811) cathodes exhibit capacity retention of 80% over 176 cycles at C/2 under a lean electrolyte condition of 3 g Ah-1 . This work provides a facile and scalable method to advance 3D lithium hosts closer to practical lithium-metal batteries.
      Cover page: A Fiber‐Based 3D Lithium Host for Lean Electrolyte Lithium Metal Batteries
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2022)
      This work reports a method of producing flexible cobalt nanowires (NWs) directly from the chemical conversion of bulk precursors at room temperature. Chemical reduction of Li6CoCl8 produces a nanocomposite of Co and LiCl, of which the salt is subsequently removed. The dilute concentration of Co in the precursor combined with the anisotropic crystal structure of the hcp phase leads to 1D growth in the absence of any templates or additives. The Co NWs are shown to have high saturation magnetization (130.6 emu g-1). Our understanding of the NW formation mechanism points to new directions of scalable nanostructure generation.
        Cover page: Synthesis of flexible Co nanowires from bulk precursors
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