Magnetostriction in Ferrites Possessing a Square Hysteresis Loop
Baltzer, Philip K.
The development of ceramic materials with an intrinsically square hysteresis loop for use as storage elements in high-speed electronic computers has been largely empirical. A fundamental understanding of the basic mechanism responsible for the square hysteresis loop is necessary for further significant improvements in these materials. The investigation reported in this paper was undertaken to obtain magnetostriction data on a compositional series of ferrites in which there exists an important variation in the character of the hysteresis loop. A significant correlation was found between the magnetostriction and the hysteresis data. The isotropic saturation magnetostriction for these polycrystalline materials was found to change sign, going through zero at the optimum composition for hysteresis-loop squareness in this compositional series. In addition, the sign of the magnetostriction at low fields, which in nearly all cases is opposite to that at high fields, also changes at this optimum composition. These data have been analyzed, and it has been concluded that the effective domain anisotropy and the polycrystalline saturation magnetostriction are zero at the optimum composition. A possible mechanism is advanced which explains the observed data as the result of a grain-to-grain alignment of the magnetic moments due to the anisotropy of the single-crystal magnetostriction. Because it presents information of general interest this thesis report, which has had only very limited distribution, is being issued as a Division 6 Report.