On the Laws of Magnetization of Ferromagnetic Single Crystals and Polycrystals. Application to Uniaxial Compounds

One of the authors (L.N.) describes the mechanism of magnetization of a ferromagnetic single crystal: the elementary domains can be classified in several groups, called “phases” each having a certain direction of the spontaneous magnetization. The variation of the total magnetization takes place in various “modes,” corresponding to the number of coexisting phases in a given field. The calculation of the magnetization curve in these various modes explains the experimental results for single crystals of iron, pyrrhotine and magnetoplumbite. The results of measurements at room temperature on this latter compound, ${\mathrm{6Fe}}_2{\mathrm{O}}_3-\mathrm{PbO}$ , are treated in greater detail. The crystal is uniaxial; for different angles of the external field with the c axis, the magnetization first increases proportionally to the field, followed by a gradual approach to saturation (except for the angles 0 and 90°). The anisotropy constant $K_1$ is first determined ($K_2$ is negligible). The two parts of the curve can be interpreted by two “modes,” with respectively, two and one “phases.” The variation of the magnetization of polycrystalline ${\mathrm{6Fe}}_2{\mathrm{O}}_3-\mathrm{BaO}$ samples can be explained by the rotation mechanism only; the crystallites are too small in size to be divided into phases. The experimental curves can be explained by taking into account the interactions between crystallites in calculating the law of approach to saturation.