Effects of Titanium upon Magnetic Anisotropy and Coercivity in Alnico Magnet Alloys

Abstract

The anisotropy measurement combined with magnetic measurement and electron microscopy is performed on monocrystalline Alnico alloys with various contents of Ti and Co, to examine the effects of these constituents, especially of Ti, upon the high coercivity in Alnico alloys. The shape anisotropy constant, K_u^* increases with Ti content in the same way the coercive force does.
According to Stoner-Wohlfarth model, the anisotropy constant can be expressed by K_u^*(cal)=p(1−p)(N_b−N_a)I_s²⁄2, where p is the packing fraction, (N_b−N_a) is the difference of demagnetization coefficients along the short and long axes, and I_s is the saturation magnetization of the precipitate particles.
Using the values obtained by electron microscopy together with magnetic measurement, the shape anisotropy constant, K_u^*(cal), is evaluated. A good agreement can be found between K_u^* and K_u^*(cal).
Consideration on several factors affecting K_u^* or _IH_c leads to the conclusion that a principal cause of the high coercivity of high titanium Alnico alloys is sought in the factor of the packing fraction of particles.