The effect of Lorentz demagnetization field (LDF) on the saturation magnetization of SmCo5 magnets

In order to have a further understanding of the cause of the increase in the saturation magnetization, 4πMs, of SmCo5 magnets in sintering, saturation magnetization as a function of density, phase change and the grain sizes were measured in this study. While Tawara and Senno considered that the increasing in 4πMs of the ‘‘Ce-Co-Fe-Cu’’ system was due to the improvement of the magnetization alignment caused by increasing the grain size during the magnet sintering process [Y. Tawara and H. Senno, IEEE Trans. Magn. MAG-8, 560 (1972)], it was shown that the Lorentz demagnetization field (LDF) [S. Chikazumi, Physics of Magnetism (Wiley, New York, 1964), Sec. 2-2; B. D. Cullity, Introduction to Magnetic Materials (Addison-Wesley, Reading, MA, 1972), Sec. 4-3, p. 132] was the major factor in the 4πMs increment after the magnet sintering. As a result of calculation by the use of the LDF in the SmCo5 system, an accuracy of ±3% was readily obtained, while that of Tawara and Senno has an accuracy of 29.6% higher than its normalized (or expected) value in their system. But if LDF was involved in the ‘‘Ce-Co-Fe-Cu’’ system, a value of +6.5% can be obtained. Finally, it was thought that the phase change occurring in sintering, e.g., Sm2Co7 to SmCo5, may be a minor factor in favor of the increasing phenomena in the system by the observation of x-ray diffraction patterns.