Anisotropy fields of Ba-ferrite and other particulate media

The anisotropy field (H/sub k/) in Co- and Ti-doped platelet-shaped particulate assemblies and in Co-modified iron oxide and very-high-coercivity metal-particle media was determined by measuring the rotational hysteresis losses as a function of the applied field and extrapolating the high-field part of the distribution to obtain the field at which the losses diminish to zero. For Ba-ferrite media with H/sub c/=550-1300 Oe, H/sub k/ values ranging from 2.2-6 kOe and not necessarily correlated with the coercivities were obtained. Co-gamma media had H/sub k/ values toward the lower part of this range, while the very-high-H/sub c/ metal particle media had H/sub k/ values in the upper part of this range, in both cases correlated with their coercivities. A high value of H/sub k/ is found to be a necessary, but not a sufficient, condition for large angular dependence of the remanence coercivity (H/sub r/). Additional requirements include single-domain particles with predominant crystalline anisotropy and a high degree of morphological perfection of the particles. A high H/sub k/, however, provides for more rectangular remanence loops (and thus reduces recording demagnetization/losses) not only when crystalline anisotropy predominates, but also, to some extent, when shape anisotropy is dominant.<
>