Magnetocrystalline anisotropy in ferrites of the form Zn2X and Co2X

Measurements of the magnetocrystalline anisotropy have been made in Ba2Zn2Fe28O46and Ba2Co2Fe28O46, two materials of the phase of hexagonal ferrites. The measurements were made by ferromagnetic resonance techniques at room temperature. The anisotropy of Zn2X was also measured by a static technique. These materials have rhombehedral symmetry, and thus are similar to the phase. The lowest terms in the anisotropy energy consistent with this symmetry are . Zn2X shows uniaxial anisotropy, with erg/cm³, K2and zero. The static measurement yielded erg/cm³. In Co2X erg/cm³, erg/cm³, erg/cm³so the unique axis becomes a hard direction. Comparison of the measured change in anisotropy on substitution of cobalt for zinc with the theory of Slonczewski shows that to second order the theory predicts just the three terms shown, and gives numerical values larger by a factor of two than the measured values. Linewidths are also reported.