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Resonant Ferromagnetic Absorption and Magnetic Characterization of Spintronic Materials

O'Dell, Ryan Andrew
http://orcid.org/0000-0002-8329-4037
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1533043360679487

Abstract Details

2018, Doctor of Philosophy, University of Toledo, Electrical Engineering.
The dynamic magnetization parameters in ferromagnetic alloys of Co40Fe40B20 and Ni60Fe40, are commonly used as spintronic free layers. I investigated these alloys to determine how deposition conditions and post deposition annealing, influence structural material properties which can be correlated to the magnetization changes. Through the varying of film thicknesses in Co40Fe40B20, the spectroscopic splitting factor increases from g = 2.16 to g = 2.67 as films reduce from 100 nm to about 8 nm. The magnetization reduces from 14708 (Oe) to 7069 (Oe) when the film thickness is reduced from 123 nm to 8 nm. The in-plane peak-to-peak linewidth and the damping increases as the film thickness is reduced with damping values of α = 0.013 at 123 nm and 0.37 at 8 nm. The perpendicular uniaxial anisotropy is believed to be the cause of these changes as it increases with the reduction of thin film thickness. The thickness of the Co40Fe40B20 does not alter the amorphous structure in any way. The in-plane coercivity of 8 nm films is greater than those which are larger. As Co40Fe40B20 is annealed, the grain size does not increase much from room temperature to 350C. However, at 370°C, secondary phase Co7Fe3 segregates from the amorphous matrix and causes shifts in the ferromagnetic resonance absorption and broadening of the linewidth. Multiple resonances can be observed in the absorption spectra, which correspond to two distinct ferromagnetic material phases. In Ni6Fe4 thin films, increased thickness improves structural quality showing narrower full width at half maximum diffraction peaks of the (111) orientation. The increased thickness however increases the ferromagnetic resonance linewidth. Two-magnon scattering of degenerate modes due polycrystallinity lead to non-linear perturbations in the linewidth at increased microwave frequencies. The damping has been found to increase from 0.017 at 30 nm to 0.026 at 131 nm as a result of this scattering. Additionally the g-factor was fitted to be g = 2.19 at 30 nm and increased to 2.54 at 131nm. Thin films of Ni6Fe4 show increased crystallinity when deposited at substrate temperatures of 200°C where both (111) and (200) diffraction peaks are clearly visible. The increased crystallinity, however, leads to increased scattering of the ferromagnetic resonance absorption line. The damping was found to depend on the substrate temperature during deposition and increases from &#945 = 0.0006 at 100°C to 0.016 at 300°C. Thin films of Co40Fe40B20 deposited at substrate temperature of 500°C begin to crystalize into secondary phase Co7Fe3. Prior to crystallization at 400°C two magnon scattering effects can be seen in the ferromagnetic absorption spectra. Increasing the deposition temperature to slightly below the crystallization point provides and optimal film as a starting point. Post deposition annealing should be limited to a temperature range below the crystallization temperature, to reduce diffusion. Low damping, high quality, ferromagnetic films can be produced when sample thickness, deposition temperature and annealing temperature are optimized.
Daniel Georgiev, PhD (Committee Co-Chair)
Michael Heben, PhD (Committee Co-Chair)
Raghav Kahanna, PhD (Committee Member)
Richard Molyet, PhD (Committee Member)
Randall Ellingson, PhD (Committee Member)
John Jones, PhD (Committee Member)
279 p.
Electrical Engineering; Electromagnetics; Electromagnetism; Physics
Ferromagnetism, Spintronics, Ferromagnetic Resonance, Spin wave, Vibrating Sample Magnetometry

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Citations

  • O'Dell, R. A. (2018). Resonant Ferromagnetic Absorption and Magnetic Characterization of Spintronic Materials [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1533043360679487

    APA Style (7th edition)

  • O'Dell, Ryan. Resonant Ferromagnetic Absorption and Magnetic Characterization of Spintronic Materials. 2018. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1533043360679487.

    MLA Style (8th edition)

  • O'Dell, Ryan. "Resonant Ferromagnetic Absorption and Magnetic Characterization of Spintronic Materials." Doctoral dissertation, University of Toledo, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1533043360679487

    Chicago Manual of Style (17th edition)

toledo1533043360679487
224
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This open access ETD is published by University of Toledo and OhioLINK.