In order to study the approach-saturation curve and determine the magnetic parameters of polycrystalline hexagonal planar ferrites we have done a series of theoretical and experimental studies. The approach-saturation expression is sigma =sigma(s)(1-aH(-1)-bH(-2)-cH(-3))+chi X(1)H. We have derived the expressions for b and c of the hexagonal materials: b = (4/15)(K-1/M(s))(2) c=(16/105)(K-1/M(s))(3). The five coefficients can be determined simultaneously by a computational method in a suitable H -region. For a Co(2)Z sample, sigma(s)=49.37 emu/g, K-1= -1.78x10(6) erg/cm(3); for a Co(1.78)Zn(0.22)Z sample, sigma(s)=50.15 emu/g, K-1= -1.72x10(6) erg/cm(3). The experimental results show that a = 0, which means that the magnetocrystalline anisotropy field in the hexagonal polycrystalline ferrites is much larger than the magnetoinhomoneity field, and thus the latter can be be neglecd.
