The rotation of the magnetization in the BaCo2Fe16O27 W-type hexagonal ferrite

Abstract

The rotation of the magnetization in the BaCo 2Fe 16O 27 W-type hexagonal ferrite has been studied by neutron powder diffraction and single crystal magnetic measurements in the (2–620 K) temperature range. From neutron powder diffraction data the magnetic structures were determined. At T = 2 K, the structure is collinear, according to the Gorter model, but the resulting spontaneous magnetization is not in the basal plane; it makes an angle, θ = 70(1.5)°, with the hexagonal c axis. This arrangement is constant up to 180° C; then a continuous rotation of the magnetization towards the c axis occurs, ending at T = 280° C. Above this temperature and untill the Curie temperature, the structure is collinear along the hexagonal axis. From magnetic measurements the magnetocrystalline anisotropy constants are determined, by using the method of Sucksmith and Thomspon, between room temperature and 350° C. At room temperature, their values are: K 1 = -3.5, K 2 = 0.8 and K 3 = 0.9 expressed in 10 6 erg/cm 3. The angles between the easy magnetization axis and c axis are deduced from the K i 's values; they bring out the quasi-planar behavior of the magnetization: θ = 69(2)° up to 180° C, together with the complete rotation to the hexagonal c axis at 280° C.