| Two of the most important properties of a soft magnet are the saturation magnetization (Ms) and the coercivity (Hc). An ideal soft magnet would have a very high saturation magnetization and a very low coercivity. In recent years, there has been considerable interest in the development of nanocrystalline materials, including magnetic materials. This is because at grain sizes less than 100nm, they exhibit many enhanced properties, for example, increased hardness and strength. With respect to magnetic applications, nano-processed materials have the additional benefit of having an increased electrical resistivity. It is because of these factors that considerable efforts have been put into the research of nanocrystalline magnets.; However, early attempts to produce such materials by several synthesis techniques have failed to achieve the expected values for the saturation magnetization. This work is concerned with the development of synthesis methods for a variety of soft magnetic materials that could surpass the saturation magnetization limitations observed in previous work. In particular, nickel-iron alloys, pure cobalt and cobalt-iron alloys, in order of increasing saturation magnetization, were produced by electrodeposition methods.; By alloying iron with nickel, binary nickel-iron alloy deposits have been successfully produced within a composition range of up to approximately 28wt.% iron. This compositional region covers that of Permalloy® (Ni-20Fe), an extremely important nickel-iron alloy for magnetic applications. The grain size of these alloys was found to be between 10nm to 25nm, and was essentially a function of the iron content in the alloy. With a maximum hardness of over 600VHN, the microhardness of these materials was significantly improved (a 6 to 7-fold increase) as compared to conventional materials with the same compositions.; In order to obtain a higher saturation magnetization, operating windows for the production of nanocrystalline pure cobalt were found using the pulsed current electrodeposition technique. These electrodeposits were found to have grain sizes between 8nm to 15nm, with microhardness values up to 650VHN, a factor of 2 to 3 increase from conventionally produced pure cobalt.; To further increase the saturation magnetization, iron was alloyed with cobalt. Cobalt-iron alloys were successfully electrodeposited with iron contents up to about 22wt.% iron. These binary alloy deposits exhibited the same three distinct phases reported using pyrometallurgical production methods. However, the phase fields were shifted, along with a difference in the compositional range each one covered. The grain size of these deposits ranged from 20nm up to micrometers, with the smallest-grained alloy deposits in the middle of the composition range produced. The maximum hardness of these binary alloy deposits was about 400VHN.; The results obtained in this work constituted the first achievement in the production of nanocrystalline soft magnets that could eventually be tailored towards the ideal magnet. |
