Mechanisms of magnetic losses in fine-grain Ni—Zn ferrites

Polycrystalline samples of nickel-zinc ferrites were used to study the dependence of the excitation threshold of spin waves on the grain size. The measurements were carried out on two series of samples. In the first, the zinc concentration was varied to change the anisotropy field, and in the second, the level of internal losses was varied by the introduction of small addition of cobalt ions. It is shown that, as the anisotropy field decreases (the coupling between grains increases) the increase of the threshold field with decreasing grain size becomes weaker. When cobalt ions are introduced, the dependence of the threshold field on the grain size disappears in the region of large grains, and the larger the cobalt-ion concentration the smaller is the grain size starting from which the threshold field ceases to depend on the grain size.