Studies Of Structure And Magnetic Properties In Perpendicular Recording Media L1₀-FePt

With the development of the information technology, and continuously increasing demand for information storage, magnetic storage, as a main storage technology, has been improved greatly. Perpendicular magnetic recording technology achieves ultra-high recording density. Since L10-FePt, due to its ultra-high magnetocrystalline anisotropy energy, has great applications in ultra-high density perpendicular magnetic recording media, it has got widespread attention. Most of studies have been focused on the trade-off issue. In order to keep good thermal stability, high perpendicular anisotropy is required. As a result, the switch field is too high for the present write heads. On the other hand, the L10-FePt films are ideal objects for studies of the magnetization reversal mechanism. In this dissertation, we have focused on the relationship between the magnetization reversal mechanism and the structure.A series of L10-FePt films with film thickness varying from8.8nm to79.2nm were fabricated on MgO(001) substrates by DC magnetron sputtering. The base pressure was4.0×1.0-5Pa and the Ar pressure0.35Pa during deposition. The Fe and Pt layers were deposited alternatively at elevated temperatures of500℃. After deposition, the samples were post-annealed at the temperature of500℃for2hours. All samples were characterized by Rigaku X-ray diffraction (XRD) and FEI Titan high resolution transmission electron microscopy (HRTEM). It is shown that all samples are of long-range chemical ordering. It is found that dislocations and nano-twins are located at the interface and in the film bulk, respectively. Magnetic properties are measured by a vibrating sample magnetometer (VSM) and VersaLab. All samples were of perpendicular magnetic anisotropy. It is found that the out-of-plane coercivity decreases greatly with the increasing film thickness at specific temperatures. It changes as a linear function of for specific samples and the slope become small for thick samples. In order to reveal the magnetization reversal mechanism, we also measured the magnetic viscosity. We find that the fluctuation field at room temperature decreases with increasing film thickness, it is therefore indicated that the thermal activation energy and volume increase with increasing film thickness. This agrees with the periodic alignment of dislocations at L10-FePt/MgO interface and the existence of defects in L10-FePt films.Besides, we also studied magnetic properties of L10-FePt/Fe and L10-FePt/TbFeCo bilayers. For L10-FePt/Fe bilayers, the interlayer coupling between the two layers will be strong if the Fe layer is deposited at the same temperature as the annealing temperature of the L10-FePt layer. It will be very weak if the Fe layer was deposited at room temperature after the L10-FePt is cooled to room temperature for about10hours. For L10-FePt/TbFeCo bilayer, the out-of-plane coercivity decreases dramatically with increasing temperature, while it decreases slightly for the L10-FePt single layer films. The above results could be helpful for heat-assisted magnetic recording technology.