Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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Access Right: Open AccessAuthor: search.filters.author.Habibzadeh, Alireza

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  • Article
    Quantum Monte Carlo Study of Artificial Triangular Graphene Quantum Dots
    (Amer Physical Soc, 2025) Kul, E. Bulut; Habibzadeh, Alireza; Cinar, M. N.; Guclu, A. D.
    We investigate the magnetic phases of semiconductor-based artificial triangular graphene quantum dots (TGQDs) with zigzag edges using variational and diffusion Monte Carlo methods. These systems serve as quantum simulators for bipartite lattices with broken sublattice symmetry, providing a platform to study the extended Hubbard model's emergent magnetic phenomena, including Lieb's magnetism at half filling, edge depolarization upon single-electron addition, and Nagaoka ferromagnetism. Our nonperturbative quantum Monte Carlo simulations, performed for finite-sized TGQDs modeled as nanopatterned GaAs quantum wells, with system sizes up to Ns = 61 lattice sites, reveal a transition from metallic to insulating regimes as a function of the quantum well radius rho, while preserving edge-polarized ground states at half filling. Notably, edge depolarization occurs upon single-electron doping in both metallic and insulating phases, in contrast to the Nagaoka ferromagnetism observed in hexagonal armchair geometries.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 6
    Microstructural Investigation of Discarded Ndfeb Magnets After Low-Temperature Hydrogenation
    (Springer, 2024) Habibzadeh, Alireza; Kucuker, Mehmet Ali; Cakir, Oznur; Gokelma, Mertol
    Due to continuously increasing demand and limited resources of rare-earth elements (REEs), new solutions are being sought to overcome the supply risk of REEs. To mitigate the supply risk of REEs, much attention has recently been paid to recycling. Despite the more common recycling methods, including hydrometallurgical and pyrometallurgical processes, hydrogen processing of magnetic scrap (HPMS) is still in the development stage. Magnet-to-magnet recycling via hydrogenation of discarded NdFeB magnets provides a fine powder suitable for the production of new magnets from secondary sources. One of the crucial aspects of HPMS is the degree of recovery of the magnetic properties, as the yield efficiency can easily reach over 95%. The amount, morphology, and distribution of the Nd-rich phase are the key parameters to achieve the excellent performance of the magnet by isolating the matrix grain. Therefore, a better insight into the microstructure of the matrix grains and the Nd-rich phase before and after hydrogenation is essential. In this study, a low-temperature hydrogenation process in the range of room temperature to 400 degrees C was conducted as the first step to recycle NdFeB magnets from discarded hard disk drives (HDDs), and the hydrogenated powder was characterized by electron microscopy and X-ray diffraction. The results show that there are three different morphologies of the Nd-rich phase, which undergo two different transformations through oxidation and hydride formation. While at lower temperatures (below 250 degrees C) the degree of pulverization is higher and the experimental evidence of hydride formation is less clear, at higher temperatures the degree of pulverization decreases. The formation of neodymium hydride at higher temperatures prevents further oxidation of the Nd-rich phase due to its high stability.
  • Review
    Citation - WoS: 41
    Citation - Scopus: 42
    Review on the Parameters of Recycling Ndfeb Magnets Via a Hydrogenation Process
    (American Chemical Society, 2023) Habibzadeh, Alireza; Küçüker, Mehmet Ali; Gökelma, Mertol
    Regarding the restrictions recently imposed by China on the export of rare-earth elements (REEs), the world may face a serious challenge in supplying some REEs such as neodymium and dysprosium soon. Recycling secondary sources is strongly recommended to mitigate the supply risk of REEs. Hydrogen processing of magnetic scrap (HPMS) as one of the best approaches for magnet-to-magnet recycling is thoroughly reviewed in this study in terms of parameters and properties. The processes of hydrogen decrepitation (HD) and hydrogenation-disproportio-nation-desorption-recombination (HDDR) are two common methods for HPMS. Employing a hydrogenation process can shorten the production route of new magnets from the discarded magnets compared to other recycling routes such as the hydrometallurgical route. However, determining the optimal pressure and temperature for the process is challenging due to the sensitivity to the initial chemical composition and the interaction of temperature and pressure. Pressure, temperature, initial chemical composition, gas flow rate, particle size distribution, grain size, and oxygen content are the effective parameters for the final magnetic properties. All these influencing parameters are discussed in detail in this review. The recovery rate of magnetic properties has been the concern of most research in this field and can be achieved up to 90% by employing a low hydrogenation temperature and pressure and using additives such as REE hydrides after hydrogenation and before sintering.