Browsing by Author "Lee, Hwachol"

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    Growth and Characterization of 144 μm Thick Barium Ferrite Single Crystalline Film for Microwave Device Application
    (2009) Jalli, Jeevan; Hong, Yang-Ki; Bae, Seok; Abo, Gavin S.; Lyle, Andrew; Gee, Sung-Hoon; Lee, Hwachol; Mewes, Tim; Sur, Jeong-Chul; Lee, Sung-Ik; ; University of Alabama Tuscaloosa
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    The magnetic and chemical structural property of the epitaxially-grown multilayered thin film
    (University of Alabama Libraries, 2012) Lee, Hwachol; Mankey, Gary J.; University of Alabama Tuscaloosa
    L10 FePt- and Fe-related alloys such as FePtRh, FeRh and FeRhPd have been studied for the high magnetocrystalline anisotropy and magnetic phase transition property for the future application. In this work, the thin film structural and magnetic property is investigated for the selected FePtRh and FeRhPd alloys. The compositionally-modulated L10 FePtRh multilayered structure is grown epitaxially on a-plane Al2O3 with Cr and Pt buffer layer at 600degC growth temperature by DC sputtering technique and examined for the structural, interfacial and magnetic property. For the epitaxially grown L10 [Fe50Pt45Rh5 (FM) (10nm) / Fe50Pt25Rh25 (AFM) (20nm)]×8 superlattice, the magnetically and chemically sharp interface formation between layers was observed in X-ray diffraction, transmission electron microscopy and polarized neutron reflectivity measurements with the negligible exchange bias at room and a slight coupling effect at lower temperature regime. For FeRhPd, the magnetic phase transition of epitaxially-grown 111-oriented Fe46Rh48Pd6 thin film is studied. The applied Rhodium buffer layer on a-plane Al2O3 (1120) at 600degC shows the extraordinarily high quality of epitaxial film in (111) orientation, where two broad and coherent peak in rocking curve, and Laue oscillations are observed. The epitaxially-grown Pd-doped FeRh on Pt (111) grown at 600degC, 700degC exhibits the co-existing stable L10 (111) and B2 (110) structures and magnetic phase transition around 300degC. On the other hand, the partially-ordered FeRhPd structure grown at 400degC, 500degC shows background high ferromagnetic state over 5K~350K temperature. For the reduced thickness of Fe46Rh48Pd6, the ferromagnetic state becomes dominant with a reduced portion of the film undergoing a magnetic phase transition. For some epitaxial FeRhPd film, the spin-glass-like disordered state is also observed in field dependent SQUID measurement. For the tri-layered FeRhPd with thin Pt spacer, the background ferromagnetic state is significantly reduced and spin-glass-like state also disappears. In polarized neutron reflectivity, magnetic depth profiles of tri-layered FeRhPd reveals the asymmetric magnetization between two FeRhPd layers. The asymmetric magnetic profile of FeRhPd tri-layered structure is closely related to the thickness dependent epitaxial film growth of B2 structure.
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    Magnetic order and phase transitions in Fe50Pt50-xRhx
    (International Union of Crystallography) Fenske, Jochen; Lott, Dieter; Tartakovskaya, Elena V.; Lee, Hwachol; LeClair, Patrick R.; Mankey, Gary J.; Schmidt, Wolfgang; Schmalzl, Karin; Klose, Frank; Schreyer, Andreas; Helmholtz Association; Helmholtz-Zentrum Geesthacht - Zentrum fur Material- und Kustenforschung; National Academy of Sciences Ukraine; Institute of Magnetism NAS of Ukraine & MES of Ukraine; University of Alabama Tuscaloosa; Australian Nuclear Science & Technology Organisation; City University of Hong Kong
    Polarized and unpolarized neutron diffraction techniques have been applied to study the temperature-dependent magnetic and structural properties of four 200 nm-thick Fe50Pt50-xRhx films with x = 5, x = 10, x = 17.5 and x = 25. Similar to the bulk system, an antiferromagnetic to ferromagnetic transition can be found in the films with decreasing Rh concentration. The application of structure factor calculations enables one to determine the microscopic magnetic configuration of the different films as a function of temperature and Rh concentration. The developed models indicate a magnetic transition from a dominant antiferromagnetic order in the out-of-plane direction to a dominant ferromagnetic order in the in-plane direction with decreasing Rh concentration. The different magnetic configurations can theoretically be described by a phenomenological model which includes a two-ion and a one-ion interaction Hamiltonian term with different temperature dependencies of the anisotropy constants.