First order magnetization processes in uniaxial crystals: (Zn,Co) 2 BaFe 16 O 27

We give the experimental evidence of first order magnetization processes in a W- -type hexaferrite single crystal having composition BaZn 1.38 Co .62 Fe 16 O 27 . 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 K 2 /K 1 and K 3 /K 1 of the anisotropy constant. Computer plots are given of the critical field and magnetization at which the transition takes place.