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Mossbauer, magnetic and structural studies of permanent-magnet alloys and multilayered films
Abstract
Mossbauer spectra and magnetization measurements of $\rm YFe\sb{12-x}Mo\sb{x},$ for $\rm 0 \le x \le 4,$ are reported and compared with self-consistent spin-polarized electronic-structure calculations. The ternary compounds $\rm YFe\sb{12-x}Mo\sb{x}$ have the crystalline tetragonal ThMn$\sb{12}$ structure. Analyses of the Mossbauer spectra show that Mo atoms occupy the 8i Fe sites of the ThMn$\sb{12}$ structure. Room temperature magnetic and Mossbauer measurements show that the compounds with x $\le$ 2.0 are ferromagnetic and with x $\ge$ 3.0 are paramagnetic. Low temperature magnetic measurements show that the magnetic ordering temperature depends on x. The calculated magnetization decreases less rapidly with increasing x than the experimental data. In general the data suggest that with increasing Mo concentration there is an increase of antiferromagnetic coupling among the Fe moments, which leads to cluster-glass or spin-glass-like phenomena. Fe$\sp{57}$ Mossbauer spectroscopy studies are reported on the effect of substituting non-magnetic elements and/or carbon doping on the magnetic properties of the Fe sites of $\rm R\sb2Fe\sb{17-x}M\sb{x}C\sb{y}$ (R = Sm, Nd; M = Al, Ga, and Si). In this study systems with $\rm 0 \le x \le 4$ and y between 0 and 3, were measured at room temperature and analyzed. The ternary compounds $\rm R\sb2Fe\sb{17-x}M\sb{x}C\sb{y}$ studied have the rhombohedral $\rm Th\sb2Zn\sb{17}$ structure with in-plane or c-axis anisotropy. The Al and Ga atoms were found to occupy the 6c, 18h, and 18f but not 9d Fe sites, while Si occupies the 18h, 18f, and 9d sites, and the fraction of occupancy of M was found to depend on x. The average hyperfine fields for $\rm R\sb2Fe\sb{17-x}M\sb{x}C\sb{y}$ were found to depend on M and/or C, which is in qualitative agreement with magnetic measurements. In these compounds alloying with C and/or M can improve the magnetic properties such as Curie temperature and magnetization which make them potential candidates for permanent-magnet development. $\rm Co\sb{80}Sm\sb{20}/Fe\sb{65}Co\sb{35}$ bilayer and multilayer films with Cr underlayers and overlayers have been fabricated and studied. All the samples prepared have in-plane anisotropy and the hysteresis loops were simple single loops for $\rm t\sb{FeCo}\ \le$ 300A indicating that the two phases are strongly exchange coupled. The magnetization of these samples was found to increase with increasing FeCo layer thickness for a fixed CoSm layer thickness. The energy products for these samples vary from about 6 MGOe at room temperature to 26 MGOe at 30 K. The shape and the behavior of the initial loops and the minor loops suggest that wall pinning is the dominant coercivity mechanism in these films. Reversible demagnetization curves were measured and found to be consistent with the behavior expected for "exchange-spring" magnets.
Subject Area
Condensation|Materials science
Recommended Citation
Al-Omari, Imaddin Ali, "Mossbauer, magnetic and structural studies of permanent-magnet alloys and multilayered films" (1996). ETD collection for University of Nebraska-Lincoln. AAI9637058.
https://digitalcommons.unl.edu/dissertations/AAI9637058