First order magnetization processes in uniaxial crystals: (Zn,Co)2BaFe16O27

We give the experimental evidence of first order magnetization processes in a W- -type hexaferrite single crystal having composition BaZn1.38Co.62Fe16O27. The nature and the characteristics of the transition change with temperature from 77 to 250°K. The observed effects are discussed on the basis of a phenomenological analysis that describes the transition in terms of the ratios K2/K1and K3/K1of the anisotropy constant. Computer plots are given of the critical field and magnetization at which the transition takes place.