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Magnetic properties of nanostructured thin films
Abstract
In this work the synthesis and properties of artificially structured magnetic materials with nanoscale structures are reported. Nanostructured materials possess physical properties that differ greatly from those of bulk materials which has led to many new applications. In this research the nanocomposite Fe:SiO$\sb2$ films and nanocrystalline rare-earth cobalt alloy films were prepared by sputtering. $\rm Fe\sb{80}(SiO\sb2)\sb{20}$ nanocomposite films consisting of Fe crystallites having a bcc structure with average grain size of 46-66 A embedded in a SiO$\sb2$ matrix. As indicated by the thickness dependence of resistivity, the stacking and connectivity of the crystallites depend on the thickness of the film. The magnetic coercivity (H$\sb{c}$) depends on the film thickness. Films prepared from a $\rm Fe\sb{70}(SiO\sb2)\sb{30}$ and $\rm Fe\sb{90}(SiO\sb2)\sb{10}$ composite targets show only weak dependence of $\rm H\sb{c}$ on film thickness. Magnetic and structural properties of nanocrystalline SmCo//Cr and PrCo//Cr films were investigated with the objective of optimizing their properties for ultra high density longitudinal recording media. The as-deposited SmCo$\sb{x}$//Cr (x = 5, 4, 3.5) films consist of nanocrystallites of about 3-5 nm in diameter, embedded in an amorphous matrix. The films have high coercivities, about 2.5 to 4 kOe, and other favorable properties. The as-deposited PrCo//Cr films are mostly amorphous with a small coercivity value but after annealing at 400 $\sp\circ$C the PrCo layer is completely crystallized with a grain size of about 10 nm resulting in a large enhancement of coercivity. Nanodiffraction and High Resolution Transmission Electron Microscopy (HRTEM) studies show that the crystallites have a closed packed hexagonal structure. The effects of Ar sputtering pressure, PrCo layer thickness, and Cr underlayer thickness on the magnetic properties were investigated. The magnetization reversal mechanism was investigated from the shape of the initial hysteresis loop, minor loops and time dependence of magnetization. The magnetic switching volume is in the range of 1 to $1.7\times 10\sp{-18}$ cm$\sp3$. By annealing the as-deposited SmCo//Cr and PrCo//Cr thin films room temperature coercivity values ranging from 1 to 45 kOe were achieved.
Subject Area
Condensation|Materials science
Recommended Citation
Malhotra, Sudhir S, "Magnetic properties of nanostructured thin films" (1996). ETD collection for University of Nebraska-Lincoln. AAI9700099.
https://digitalcommons.unl.edu/dissertations/AAI9700099