The Coercivity of Hard Ferrite Single Crystals

Magnetic properties of Sr‐, Ba‐ and Sr‐Ba‐ferrite single crystals are reported. From torque measurements results: Sr‐ferrite: M s = (380 ± 20) G, K 1 = (3.5 ± 0.1) × 10 6 erg cm −3 ; Ba‐ferrite: M s = (380 ± 20) G, K 1 = (3.2 ± 0.1) × 10 6 erg cm −3 . A large difference was found by a comparison of H ci, theor (coherent rotation) with H ci, meas (oriented Sr‐ferrite magnet). The very small (generally even positive) nucleation fields, measured on single crystal plates of different chemical composition and different crystal sizes can qualitatively explain the low values and the grain size dependence of H ci .