Ali Baghi Zadeh


Last Name

Baghi Zadeh

First Name

Ali

ORCID

0000-0001-7633-6326

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2020 - 20255
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Publications 1 - 5 of 5
  • Effect of periodicity on the magnetic anisotropy in spinel oxide superlattices
    Item type: Journal Article
    Motti, Federico; Riddiford, Lauren J.; Vaclavkova, Diana; et al. (2023)
    Physical Review B
    Metamaterials, fabricated by assembling different compounds at the nanoscale, can have properties not found in naturally occurring materials, and therefore offer new avenues to develop novel devices. In the realm of spintronics, where the spin of the electrons is used to extend the capabilities of electronic devices, the quest for such new functional materials has expanded towards magnetic oxides. Here, finding methods to control their magnetic anisotropy is crucial to achieve higher memory density and longer stability. In order to address this challenge, we combined two oxides with a spinel crystal structure, synthesizing CoCr₂O₄/CoFe₂O₄ superlattices with layers only few unit cells thick. We show that the superlattices present a reorientation of the magnetic easy axis from in plane to out of plane when warmed up, at a temperature determined by the periodicity. We can describe this with a model that includes the strain-induced anisotropy of the two materials and their different temperature dependence. This approach to create artificial materials, involving engineering superlattices to tailor the magnetic anisotropy, can be generalized to a wide range of compounds that can be grown strained on suitable substrates.
  • Control over epitaxy and the role of the InAs/Al interface in hybrid two-dimensional electron gas systems
    Item type: Journal Article
    Cheah, Erik; Haxell, Daniel Z.; Schott, Rüdiger; et al. (2023)
    Physical Review Materials
    In situ synthesized semiconductor/superconductor hybrid structures became an important material platform in condensed matter physics. Their development enabled a plethora of novel quantum transport experiments with focus on Andreev and Majorana physics. The combination of InAs and Al has become the workhorse material and has been successfully implemented in the form of one-dimensional structures and two-dimensional electron gases. In contrast to the well-developed semiconductor parts of the hybrid materials, the direct effect of the crystal nanotexture of Al films on the electron transport still remains unclear. This is mainly due to the complex epitaxial relation between Al and the semiconductor. Here, we present characterization of Al thin films grown on shallow InAs two-dimensional electron gas systems by molecular beam epitaxy. Using a growth approach based on an intentional roughening of the epitaxial interface, we demonstrate growth of grain-boundary-free Al. We show that the implemented roughening does not negatively impact either the electron mobility of the two-dimensional electron gas or the basic superconducting properties of the proximitized system. This is an important step in understanding the role of properties of the InAs/Al interface in hybrid devices. Ultimately, our results provide a growth approach to achieve a high-degree of epitaxy in lattice-mismatched materials.
  • Spatially Resolved Diffusion of Aluminum in 4H-SiC During Postimplantation Annealing
    Item type: Journal Article
    Müting, Johanna; Bobal, Viktor; Willinger, Marc; et al. (2020)
    IEEE Transactions on Electron Devices
    The fabrication of power semiconductor devices based on 4H-silicon carbide (SiC) typically includes doping by ion implantation and postimplantation annealing to activate the implanted dopants. The high-temperature annealing process can initiate various diffusion mechanisms that alter the initial implantation profile in terms of spatial distribution and doping concentration. To investigate the diffusion of aluminum, the main p-dopant in 4H-SiC, samples are prepared by ion implantation and subsequent annealing at 1650 °C for 30 min. Secondary ion mass spectrometry (SIMS) measurements before and after the annealing process are performed to monitor the aluminum concentration. A significant amount of aluminum moves toward the surface and into the lateral direction, which is shown to be directly related to the implantation-induced point defects. Transmission electron microscopy (TEM) images support the discussion of diffusion mechanisms and their dependence on the defect type.
Publications 1 - 5 of 5