Systematic analyses of anomalous torque curves in granular BaFe₁₂O₁₉/SiO₂/Si thin films

An anomaly has been observed in the magnetic torque curve of BaFe₁₂O₁₉ films grown on a SiO₂/Si substrate. The kink in the torque curve has a strong dependence on the film thickness and appears when the field direction is close to the film plane. Structural analyses together with the support of magnetic loop measurements reveal a polycrystalline structure, with magnetic properties strongly dependent on film thickness. At low thicknesses, a granular structure with a perpendicular c-axis is dominant, whereas, at large thicknesses, a new texture with a tilted c-axis (61° from the film plane! is well developed. By considering the contribution of both types of grains, the shape of torque curve is well predicted and the kink origin is attributed to the tilt of the c-axis.