Magnetic materials and permanent magnets are one of the important electric and electronic materials applied in an extensive range from various electrical appliances for domestic use to peripheral terminal devices of large-scaled computers. In view of recent needs for miniaturization and high efficiency of electric and electronic equipment, there has been an increasing demand for upgrading of permanent magnets and in general magnetic materials.
Now, referring to the permanent magnets, typical permanent magnet materials currently in use are alnico, hard ferrite and rare earth-cobalt magnets. With a recent unstable supply of cobalt, there has been a decreasing demand for alnico magnets containing 20-30 wt % of cobalt. Instead, inexpensive hard ferrite containing iron oxides as the main component has showed up as major magnet materials. Rare earth-cobalt magnets are very expensive, since they contain 50-65 wt % of cobalt and make use of Sm that is not much found in rare earth ores. However, such magnets have often been used primarily for miniaturized magnetic circuits of high added value, because they are by much superior to other magnets in magnetic properties.
If it could be possible to use, as the main component for the rare earth elements, light rare earth elements that occur abundantly in ores without recourse to cobalt, the rare earth magnets could be used abundantly and with less expense in a wider range. In an effort made to obtain such permanent magnet materials, R-Fe.sub.2 base compounds, wherein R is at least one of the rare earth metals, have been investigated. A. E. Clark has discovered that suputtered amorphous TbFe.sub.2 has an energy product of 29.5 MGOe at 4.2.degree. K., and shows a coercive force Hc=3.4 kOe and a maximum energy product (BH)Max=7 MGOe at room temperature upon heat treatment at 300.degree.-500.degree. C. Reportedly, similar investigations on SmFe.sub.2 indicated that 9.2 MGOe was reached at 77.degree. K. However, these materials are all obtained by sputtering in the form of thin films that cannot be generally used as magnets for, e.g., speakers or motors. It has further been reported that melt-quenched ribbons of PrFe base alloys show a coercive force Hc as high as 2.8 kOe.
In addition, Koon et al discovered that, with melt-quenched amorphous ribbons of (Fe.sub.0.82 B.sub.0.18).sub.0.9 Tb.sub.0.05 La.sub.0.05, Hc of 9 kOe was reached upon annealing at 627.degree. C. (Br=5 kG). However, (BH)max is then low due to the unsatisfactory loop squareness of magnetization curves (N. C. Koon et al, Appl. Phys. Lett. 39 (10), 1981, pp. 840-842).
Moreover, L. Kabacoff et al reported that among melt-quenched ribbons of (Fe.sub.0.8 B.sub.0.2).sub.1-x Pr.sub.x (x=0-0.03 atomic ratio), certain ones of the Fe-Pr binary system show Hc on the kilo oersted order at room temperature.
These melt-quenched ribbons or sputtered thin films are not any practical permanent magnets (bodies) that can be used as such. It would be practically impossible to obtain practical permanent magnets from these ribbons or thin films.
That is to say, no bulk permanent magnet bodies of any desired shape and size are obtainable from the conventional Fe-B-R base melt-quenched ribbons or R-Fe base sputtered thin films. Due to the unsatisfactory loop squareness (or rectangularity) of the magnetization curves, the Fe-B-R base ribbons heretofore reported are not taken as the practical permanent magnets materials comparable with the conventional, ordinary magnets. Since both the sputtered thin films and the melt-quenched ribbons are magnetically isotropic by nature, it is indeed almost impossible to obtain therefrom magnetically anisotropic (hereinbelow referred to "anisotropic") permanent magnets for the practical purpose.
USPTO Backgrounds
USPTO Backgrounds