Huaqing Yin

Physical principles of microwave assisted magnetic recording

While the basic physics of Microwave Assisted Magnetization Reversal (MAMR) phenomenon is well established both theoretically and experimentally, its application in a practical magnetic recording environment was so far studied primarily with the help of micromagnetic recording models. In this work, we instead attempt to use analytical formulation and simple numerical models to understand the main challenges as well as benefits that are associated with such a system. It appears that the main difference between the previously introduced theory [G. Bertotti et al., Phys. Rev. Lett. 86, 724 (2001); K. Rivkin et al., Appl. Phys. Lett. 92, 153104 (2008); S. Okamoto et al., J. Appl. Phys. 107, 123914 (2010).] and recording environment is that both the RF and DC magnetic fields are applied at a substantial angle to the anisotropy axis. While the associated symmetry breaking prevents one from describing the reversal process explicitly, it is possible to approximate the solutions well enough to satisfactorily match numerical models both in the case of wire and Spin Torque Oscillator generated RF fields. This approach allows for physical explanation of various effects associated with MAMR such as high gradient of writeable anisotropy and reduction of track width, and offers a clear guidance regarding future optimization of MAMR recording.

Practical FeCo Films for Perpendicular Writer Pole

An attempt is made in this publication to review various developments of FeCo films for recording heads in the last decade and to look at emerging developments regarding these films. A series of FeCo films from 100% Fe to 100% Co was sputter deposited, characterized, and analyzed for various magnetic properties such as magnetostriction, uniaxial anisotropy, coercivity, dispersion, and saturation magnetization. Many process parameters, with the most influencing parameter being sputter pressure, play an important role especially influencing dispersion and/or hard axis coercivity (Hch) in these materials. Out of the many developments to date the effect of seed layer(s) in reducing grain size of high moment bcc FeCo films is still intriguing and, hence, a comprehensive review and analysis of seed layer effects are included. Although film stress can play an important role in optimizing Hch, there is no clear trend seen between film stress and Hch when viewed across broad processing conditions. Higher Hk evolution with oblique deposition is an interesting phenomenon in these films. Uniaxial anisotropies of nearly 1000 Oe were found. The anisotropy evolution is explained through magnetoelastic energy and through crystal structure. Even though these films are very columnar in nature it was found that there was little to no fiber texture present in these films and there was no difference in texture between fine grained and coarse grained FeCo films.

Head and Media Design for Curvature Reduction in Heat-Assisted Magnetic Recording

Recording curvature in magnetic data-storage technology has long been one of the significant challenges impacting on recording performance. Despite curvature occurrence in the conventional recording techniques such as perpendicular magnetic recording (PMR), heat-assisted magnetic recording (HAMR) is demonstrated to induce much more severe curvature than PMR. HAMR curvature could cause poor bit error rate and limits the maximum areal density capacity. Here we have theoretically predicted and demonstrated various approaches for curvature reduction from the aspect of either altering the near-field transducer head design or recording medium design. Optical and thermal modeling have indicated that by utilizing a crown-shape peg to change the thermal source profile and compensate for thermal expansion and rounding effect, it could potentially improve curvature figure of merit (FOM) and achieve curvature reduction by ~45%. In terms of the recording media design, by altering the heat sink and internal layer media material or geometry, it could also achieve curvature cancellation of ~40% with increased thermal gradient. The combined approach from both HAMR head and media perspectives with balanced recording FOMs, could potentially realize significant curvature reduction to be of similar or better recording curvature level to PMR.