UA cloudflare authentication

Browsing by Author "Singh, Amit V."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Bulk Single Crystal-Like Structural and Magnetic Characteristics of Epitaxial Spinel Ferrite Thin Films with Elimination of Antiphase Boundaries
    (Wiley-VCH, 2017) Singh, Amit V.; Khodadadi, Behrouz; Mohammadi, Jamileh Beik; Keshavarz, Sahar; Mewes, Tim; Negi, Devendra Singh; Datta, Ranjan; Galazka, Zbigniew; Uecker, Reinhard; Gupta, Arunava; University of Alabama Tuscaloosa; Department of Science & Technology (India); Jawaharlal Nehru Center for Advanced Scientific Research (JNCASR); Leibniz Institut fur Kristallzuchtung (IKZ)
    Spinel ferrite NiFe2O4 thin films have been grown on three isostructural substrates, MgAl2O4, MgGa2O4, and CoGa2O4 using pulsed laser deposition. These substrates have lattice mismatches of 3.1%, 0.8%, and 0.2%, respectively, with NiFe2O4. As expected, the films grown on MgAl2O4 substrate show the presence of the antiphase boundary defects. However, no antiphase boundaries (APBs) are observed for films grown on near-lattice-matched substrates MgGa2O4 and CoGa2O4. This demonstrates that by using isostructural and lattice-matched substrates, the formation of APBs can be avoided in NiFe2O4 thin films. Consequently, static and dynamic magnetic properties comparable with the bulk can be realized. Initial results indicate similar improvements in film quality and magnetic properties due to the elimination of APBs in other members of the spinel ferrite family, such as Fe3O4 and CoFe2O4, which have similar crystallographic structure and lattice constants as NiFe2O4.
  • Thumbnail Image
    Item
    Pulsed laser deposited epitaxial oxide thin films for microwave and spintronics applications
    (University of Alabama Libraries, 2018) Singh, Amit V.; Gupta, Arunava; University of Alabama Tuscaloosa
    Oxides are an important class of materials exhibiting properties useful in the modern technological applications. A wide range of oxides are inherently stable, both chemically and thermodynamically. Some members of the oxide family display ferroelectric, ferromagnetic and multiferroic characteristics etc., which are important for next generation non–volatile memory and microwave applications. For example, ferrites are particularly interesting due to their high magnetization, high Neel/Curie temperatures and insulating nature which aids in fabricating more efficient spintronic devices. In this work we address two crucial problems existing in the path of successful application of ferroelectric material-based spintronic memory and ferrite-based microwave devices. First, ferroelectric tunnel junctions that have a metal top electrode (also used as interconnects) are unstable due to uncompensated depolarizing field. This makes the memory devices to lose the stored information over time. We show that this problem can be addressed by introducing a ferroelectric–dielectric barrier layer in the tunnel junction. Second, a specific structural defect referred to as antiphase boundary is present in all spinel ferrite thin films reported in the literature. This type of defect significantly degrades the structural and magnetic properties of the spinel ferrite thin films as compared to their bulk counterparts and hinders the utilization of ferrite thin films for potential applications. We show that these defects can be eliminated in nickel ferrite thin films by using isostructural substrates that have a small lattice mismatch (<0.8%) and thereby obtain magnetic and microwave properties comparable to the bulk single crystal. We demonstrate that this principle can also be applied to other members of ferrite family (magnetite, cobalt ferrite etc.) to obtain improved structural and magnetic properties. In magnetite thin films grown on isostructural and lattice-matched substrates, we do not find any antiphase boundaries and hence the magnetic properties are much improved along with sharp metal to insulator transition at temperature close to that of bulk.
  • Thumbnail Image
    Item
    Study of Structural and Ferromagnetic Resonance Properties of Spinel Lithium Ferrite (LiFe5O8) Single Crystals
    (2015) Pachauri, Neha; Khodadadi, Behrouz; Althammer, Matthias; Singh, Amit V.; Loukya, B.; Datta, Ranjan; Iliev, Milko; Bezmaternykh, Leonard; Gudim, Irina; Mewes, Tim; Gupta, Arunava; University of Alabama Tuscaloosa