Hard Magnetic Thin Films

Hard magnetic films have a broad application area ranging from magnetic recording media to microelectromagnetic devices. A challenge for recording media is the 60% annual increase in areal density, which requires ever smaller magnetic dots. However, for a given magnetic anisotropy the reduction of dot size is limited, since below a critical magnetic volume the magnetisation becomes thermally unstable. For conventional media, this so called superparamagnetic limit is expected to be reached by 2005. In order to allow for further size reduction, materials with a higher magnetic anisotropy are needed. Likewise, the miniaturisation of microelectromagnetic devices requires magnetic films with high coercivity and remanence in order to provide strong magnetic forces even at reduced sizes. Promising candidates in both fields are rare-earth transition metal compounds such as NdFeB and SmCo where the IFW already possesses a high competence for bulk material. When prepared as thin films, the materials can be grown with complementary magnetic textures. NdFeB films typically possess a perpendicular magnetic anisotropy with the easy magnetisation axis perpendicular to the substrate, whereas for SmCo films the easy axis commonly lies within the film plane. A good texture can double the remanence compared to isotropic samples and is essential for applications such as perpendicular recording. Therefore we focus on textured films grown on heated substrates and examine the correlation between preparation conditions, microstructure and magnetic properties. For film deposition a UHV pulsed laser deposition cluster with two deposition chambers connected via a loadlock was designed. The automated setup was realized with support of the IFW Forschungstechnik and allows deposition of alloys and multilayers from elemental targets. The cluster provides the possibility of insitu RHEED and Auger spectroscopy (Fig. 1).