Browsing by Author "Kubota, Yukiko"

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    The FePt L10 Phase Transformation in Thin Films using Multiple Laser Pulsing
    (2010-03-04) Inaba, Yuki; Thompson, Gregory B.; Harrell, J. W.; Klemmer, Tim; Kubota, Yukiko; University of Alabama Tuscaloosa
    A series of ≈12 nm thick FePt thin films deposited onto glass substrates have been annealed with multiple 1064 nm wavelength laser pulses. The fluence was varied using pulse widths of 10.0, 5.0, and 2.5 ms. The peak temperature for each individual pulse was kept near 700 °C. The A1 to L10 phase transformation was confirmed by x-ray diffraction. A single pulse was not sufficient to obtain a fully ordered state. A maximum order parameter of 0.89 and coercivity of 10.6 kOe was obtained after 5×10 ms pulses. This particular annealed film showed the greatest amount of grain growth with a mean size of 55.1 nm. This grain size is 20% smaller than that of a furnace annealed sample which was annealed for 60 s and yielded an approximately equivalent order parameter. Similar order parameters, grain sizes, and coercivity values were observed for films that had equivalent total annealing times regardless of pulse widths.
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    Time-Temperature-Transformation Measurements of FePt Thin Films in the Millisecond Regime Using Pulse Laser Processing
    (2010-11-19) Inaba, Yuki; Zana, Iulica; Swartz, Caleb; Kubota, Yukiko; Klemmer, Tim; Harrell, J. W.; Thompson, Gregory B.; University of Alabama Tuscaloosa
    A section of the time-temperature-transformation TTT curve has been measured in the millisecond regime to describe the A1 to L10 transformation of 10 nm FePt thin films. Short time annealing was accomplished using a pulsed neodymium-doped yttrium aluminum garnet laser operating at a wavelength of 1064 nm. The temperature-time profile of the films was measured using an optical pyrometer and a platinum thin film resistor and it was numerically modeled. Effective thermal pulse widths were determined from the time dependence of the atomic diffusion coefficient calculated from the measured temperature profile. The measured TTT diagram involving average order parameter is consistent with theoretical predictions of TTT diagrams involving ordered volume fraction and shows that partial ordering can be obtained with a single effective thermal pulse as short as 1.1 ms.