Microstructural and magnetic properties of polycrystalline and epitaxial permalloy (Ni80Fe20) multilayered thin films

Citation

Hashim, Imran (1994) Microstructural and magnetic properties of polycrystalline and epitaxial permalloy (Ni80Fe20) multilayered thin films. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/X1XA-W810. https://resolver.caltech.edu/CaltechETD:etd-11302007-112544

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Permalloy ([...]) thin films are of great scientific and technological interest because of their unique soft magnetic properties, and applications to magnetic recording. Chapter 1 provides an introduction to magnetic and magnetotransport properties of [...] thin films, and how the film microstructure affects these properties. Chapter 2 discusses the instrumentation used for thin film fabrication, and for magnetic and structural characterization. Further details of instrumentation are discussed in Appendix A. Typically, the [...] films for magnetoresistive applications are capped with a refractory metal thin film such as Ta to prevent its oxidation and corrosion. We investigated the interdiffusion kinetics of polycrystalline Ta/[...] thin films and found that for 400 [...] T [...] 600'C, there was significant grain-boundary interdiffusion which drastically affected soft magnetic properties of [...]. In Chapter 3, we present details of the microstructural evolution of these multilayers and the subsequent effects on their magnetic properties. An alternate method for reducing grain-boundary scattering would be to fabricate grain-boundary free epitaxial [...] films. The epitaxy of [...] on MgO, NaCl and Cu had been demonstrated by investigators as early as the 60s. However, none of these substrates are available with as good atomic flatness as Si wafers. Following reports of epitaxial growth of Cu on Si[1], we proposed using it as a seed layer for growing [...] epitaxially on Si. However, there were conflicting reports of Cu epitaxy on Si, as some investigators claimed that Cu epitaxy on Si in UHV was not possible[2]. We were able to resolve some of these controversies (see Chapter 4 for details) and thus fabricate epitaxial Ni80Fe20 films on Cu/Si. Chapter 5 examines the effect of the lattice mismatch between Cu and [...] and the subsequent strain, on the soft magnetic properties of [...]. To explain these experimentally observed magnetic properties, a micromagnetic model was developed taking into account domain wall interaction with misfit dislocations and film surface roughness especially during the initial stages of epitaxial growth. Finally, epitaxial growth of [...]/Cu on Si suggests the possibility of growing grain-boundary free atomically sharp [...]/Cu multilayers which exhibit recently-discovered "giant" magnetoresistance. [1] C.A. Chang, Appl. Phys. Lett. 55, 2754 (1989). [2] B.P. Tonner, J. Zhang, X. Chen, Z-L. Han, G.R. Harp, and D.K. Saldin, J. Vac. Sci. Technol. B10, 2082 (1992).

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