| With the rapid increase in magnetic recording density, the area of a single recorded bit becomes smaller and smaller. In this case, two problems should be considered:the first is so called "superparamagmetic limit"; the other one is how to realize the read/write of information on the recorded bit of smaller area. Micromagnetic Simulation of Mi-cromagnetic theory in combination with numerical computing is believed to be the new magnetic research field. It can simulate magnetic hysteresis loop, permeability, mag-netic domain, magnetic spectrum and the read/write of information, provide guidance for experiment, explain the experimental results and verify the theoretical prediction.In this article, we introduce the research of ultrahigh recording-density material, mi-cromagneitc simulation theory and method. Combining the research activities and re-sults in our lab, we studied L10 ordered FePt thin film for ultrahigh density perpendicular recording media. In this work, a 3D micromagnetic model is set up for the FePt/IM/CrW monolayer (IM:Interlayer Pt/W) deposited by magnetic sputtering experimental meth-ods. The basic magnetic characteristics of the FePt medium is analyzed according to the relationship between the magnetic property and the microstructure, with careful discus-sions of the tetragonal symmetry and the magneto-elastic anisotropy due to the stress in the film plane. The stress state in the film was analyzed and its effect on magnetic properties were discussed.Firstly, we studied studied the role of tetragonal anisotropy on the M-H loop prop-erties by using the micromagnetic method. For example, FePt thin film with W in-terlayer, when the magnetic tetragonal anisotropy Kc is 0, the loop is uniform mag-netic anisotropy out of the film. With the increase of Kc, the coercivity and saturation field in plan of film increase significantly, but coercivities and loop squareness in the perpendicular-to-plane direction of FePt film decrease. For both film with different in-terlayer. the coercivity in plan correspond with out of plan, it is because that the large tetragonal anisotropy in plan lead to comparatively large cubic anisotropy.In addition, we analysis the origin of the stress in plane of FePt film and the magni-tude. In the FePt film, when the W content in the Cr underlayer is increased from 0% to 15%. the lattice constant of CrW alloy and the misfit between the Cr(200) and FePt(001) are increased, too. which suggests that the tensile stressσ, exits in the FePt phase's film plane. Through the qualitative analysis of the film stress, the total stress in FePt film with W interlayer is about 570MPa, which contains both the intrinsic and thermal components of stress, and total film stress along the FePt phase's a-axis. It is agree well with the simulate results (about 544M Pa). For the FePt film with Pt interlayer, if we consider only the intrinsic stress (about 799MPa), both of simulated results and analy-sis coincided well with experimental results. This is mainly due to the fact that addition of Pt interlayer suppress the diffusion of Cr in underlayer into the FePt magnetic layer, as well as the stress of both layers.
|
PDF Full Text Request