A general sum rule has been established recently, bounding the integral of the gyromagnetic losses weighted by the frequency, by the square of the saturation magnetization [O. Acher and A. L. Adenot, Phys. Rev. B 62, 11324 (2000)]. This rule has been established for soft materials with internal anisotropy fields small compared to Bs. In this article, this result is extended to the case of hexagonal ferrites with strong planar anisotropy. It is shown that the bound on the integral is a simple expression of the saturation magnetization and of the out-of-plane anisotropy field. Experimental results on polycrystalline (Ba3Co2Fe24O41)-Co2Z and (BaCo1.25Ti1.25Fe9.5O19)-M hexagonal ferrites are presented. It is shown that the dynamic properties measured up to 18 GHz are bounded in agreement with our predictions.

No abstract

No abstract