TWO-PHASE MAGNETIC CHARACTER OF FePt / Si THIN FILMS
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Title of Thesis: TWO-PHASE MAGNETIC CHARACTER OF
FePt / Si THIN FILMS
Zahrah Alyousef, M.S., May 2020
Research Advisor and Chair: Abdellah Lisfi, Ph.D.
Department of Physics
Discovery of materials with large magnetization and giant magnetic
anisotropy has been the driving factor for enhancing data storage capacity in hard disk
drives. In the past 20 years the data storage technology has seen a considerable
increase in the storage capacities due to the shift from Longitudinal Magnetic
Recording (LMR) to Perpendicular Magnetic Recording (PMR). Next generation
technology like Heat Assisted Magnetic Recording (HAMR) and Microwave Assisted
Magnetic Recording (MAMR) has the potential to extend the areal density of the
recording media at least 10 times more than the current available media. FePt is a
promising material for such applications due to its high magnetic anisotropy energy
(Ku ~108 erg/cc) and large magnetization (1140 emu/cm3
). The large magnetic
anisotropy allows magnetically stable small grains, which is the requirement for
overcoming the superparamagnetic limit.
Two-Phase magnetic character of granular FePt/Si films (10 nm-150 nm thick)
with random magnetic anisotropy has been investigated through hysteresis loops,
torque curve and remanence measurements (IRM and DCD). The hysteresis loops of
films at lower temperature display soft magnetic phase only due to their cubic
structure and the films prepared at higher temperature display double switching due to
the presence of the hard and soft magnetic phases. This double switching is a
unique feature of FePt films prepared on Si substrate only. The structural
characterization performed with XRD and AFM displays polycrystalline behavior
with small grains (0.1 μm) at low temperature films and an island-like structure with
small grains surrounding the islands at high temperature films. The small grains
surrounding the islands could be the reason for double switching due to the
coexistence of soft and hard magnetic phase in the high temperature films.