Date of Award
8-2025
Degree Type
Dissertation
Degree Name
Ph.D.
Degree Program
Engineering and Applied Science - Physics
Department
Physics
Major Professor
Prof. Leszek Malkinski
Second Advisor
Prof. Ashok Puri
Third Advisor
Assoc. Prof. Damon Allen Smith
Fourth Advisor
Prof. David Hui
Fifth Advisor
Prof. Weilie Zhou
Abstract
The goal of this research was to create thin films with induced helical anisotropy and investigate magnetic properties of such films and their patterns. An alloy of 20% iron and 80% nickel (permalloy) was used because of very small magnetocrystalline anisotropy and magnetostriction. First, an unconventional method was used to deposit films with uniaxial anisotropy by sputtering the films onto silicon substrates in the presence of a uniform field of 50 Oe along the substrate plane. This resulted in magnetic atom pairs ordering along direction of the field during film growth. Shapes of hysteresis loops measured at different angles were consistent with the Stoner-Wohlfarth model of uniaxial anisotropy. Further, this method was used to induce helical anisotropy in thin films by rotating the sample relative to the applied field after deposition of subsequent layers with thickness of a few nanometers. Films with anisotropy axis twist of 90° and 180° had thicknesses of 18, 45, 90, and 180 nm. Films were patterned in the form of arrays of discs with radii of 5, 10, 20, 50, and 100 µm. Vibrating sample magnetometry was used to study magnetic properties of the films and patterns with uniaxial anisotropy, helical anisotropy, and reference isotropic samples deposited without field. It was found that hysteresis loops of the films with helical anisotropy had significantly smaller coercive force and saturation magnetization than the isotropic films or films with uniaxial anisotropy, for any direction measured in the substrate plane and out of the substrate plane. Thin film patterns with helical anisotropy and radii of 20 µm or less displayed unusual shapes of hysteresis loops, with sudden drop of magnetization at positive fields, almost zero coercivity, and linear characteristics. These attributes can be ascribed to the formation of helical spin structure in the films with helical anisotropy. The formation of such structure is easier for thicker film patterns. Further evidence of helical anisotropy was provided by magnetization versus angle measurements, which differed for clockwise and counterclockwise field rotations. The new method can be used to create a variety of spin arrangements in alloys in which pair ordering induces magnetic anisotropy.
Recommended Citation
Hasan, Md Mahmudul, "Induced Helical Anisotropy in Permalloy Thin Films and Patterns" (2025). University of New Orleans Theses and Dissertations. 3297.
https://scholarworks.uno.edu/td/3297
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