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URN etd-0119112-122505 Statistics This thesis had been viewed 2004 times. Download 769 times. Author Jui-Kuo Mei Author's Email Address No Public. Department Materials Engineering Year 2011 Semester 1 Degree Ph.D. Type of Document Doctoral Dissertation Language zh-TW.Big5 Chinese Page Count 319 Title Study on structure, phase transition, preferred orientation, and internal stress of FePt thin films treated by rapid thermal annealing Keyword FePt thin films RTA RTA FePt thin films Abstract Order-disorder transformation and the formation of (001) preferred orientation induced by rapid thermal annealing (RTA) in FePt thin films grown on amorphous glass substrates at room temperature (RT) were systematically investigated. The results showed that the FePt films with thickness (t) in the range of 10 to 100 nm are fully ordered under the post annealing conditions of heating rate (Rheat) of 80˚C/sec, annealing time (τ) of 120 sec, and annealing temperature (Ta) ≥ 700˚C. (001) preferred orientation was obtained in the samples with t ≤ 30 nm. For the samples with Rheat = 40˚C/sec, and Ta = 900˚C, (001)-texture appears at t ≤ 20 nm. Optimized (001)-texture with very high LOF factor of 0.92 was achieved at conditions of Rheat = 80˚C/sec, Ta = 800˚C, τ = 120 sec, and t = 30 nm.
Ordered FePt films with order parameter (Sord) exceeded 0.54 show remarkable hard magnetic properties. The longitudinal coercivity (Hc//) was in the range of 5 kOe to 13.8 kOe. For those samples with Sord < 0.54, the values of Hc are between 0.8 to 2 kOe. Perpendicular coercivity (Hc?) depends strongly on LOF. When LOF is higher than 0.78, the value of out-of-plane Hc is greater than the in-plane value by 50%. The optimized sample (LOF = 0.92) shows outstanding perpendicular magnetic properties including large Hc? = 8.1 kOe, small Hc// = 1.9 kOe, saturation magnetization of 526 emu/cm3, remanence of 447 emu/cm3.
The results of surface morphology indicate the formation of discontinuous island-like or network structure in the high-Ta annealed (900˚C) films with fast Rheat (80˚C/sec), drastically increases the rms surface roughness (Rrms) to tens of nanometers. On the contrary, low-Ta prepared (≤ 600˚C) samples exhibits continuous layer morphology with relatively small Rrms of about several nm even in the films with reduced t. The magnetic domain structures also show significant differences between the samples. Single domain particles and interaction domains with strong magnetic contrast were found in the films with good (001)-texture and large t (100 nm), respectively. Dependence that the (001)-texture is proportional to the lateral grain size was observed, relating the formation of preferred orientation to the internal stress/strain of the FePt films. The results of the analysis on the residual stress/strain reveal that for the RT-deposited films, the tensile initial stress of about 1 GPa is independent of t; however, for those films with (001)-texture, the tensile residual stress increases drastically from 1.6 to 8.9 GPa, directly evidencing that the internal stress/strain is an important driving force for the development of (001) texture.
In the samples with Rheat = 80˚C/sec, Ta = 900˚C, and τ = 60 sec, and t = 30 nm, a metastable phase of FePt was identified in the thickness range of 40 to 100 nm. The phase is chemically ordered with a face-centered-cubic structure and is magnetically soft. The formation of this metastable structure was found to be very sensitive to annealing condition.
Additionally, we have found that the initial stress/strain of the RT-deposited FePt films can be well controlled with the range of compressive 1.01 GPa to tensile 0.18 GPa by adjusting various deposition parameters such as working pressure, biasing voltage, sputtering powers, etc. Different initial stress/strain state was confirmed to produce distinct preferred orientation of the FePt films. Compressive initial stress/strain results in isotropic grain growth; yet, tensile stress/strain facilitates the development of (001) texture.
Advisor Committee Lin, Hong-Ming - advisor
Files Date of Defense 2011-12-30 Date of Submission 2012-01-19