We have studied the lattice parameter changes of L10 FePt nanoparticles annealed to near equilibrium as a function of composition by x-ray diffraction. We have found that the (111) diffraction peak shifts linearly with composition, however, the c parameter mostly changes in the Pt rich compositions and the a parameter mostly changes in the Fe rich compositions with respect to the equiatomic composition. This causes the tetragonality of the L10 structure to be maximized near the Fe 50%/Pt 50% composition. The magnetic properties were measured at room temperature and at 5 K and are correlated to the structural changes occurring as a function of composition.
Dynamic remanent hysteresis loops were measured at several time scales for a L10 ordered Fe45Pt55 nanoparticle array sample. At a fixed percentage of magnetization switched, Sharrock’s formula was applied to obtain both the thermal stability factor and the intrinsic switching field. From the magnetization dependence of the thermal stability factor, the width of the thermal energy barrier distribution was determined to be about 0.30. In comparison with the particle volume distribution width obtained from transmission electron microscopy, the energy barrier width is reduced significantly due to strong interparticle exchange interaction. The magnetization dependence of the intrinsic switching field was used to obtain the intrinsic, i.e., short time, remanent magnetization curves. The intrinsic switching field distribution width was found to be 0.34.
As track density increases, it has become even more critical to understand the track edge. In this study, the impact of media design on the track edges in perpendicular magnetic recording has been investigated. This study shows that soft under layer thickness and intergranular exchange coupling have significant impact on both track edge erasure and write width. In the range we studied, head-tokeeper spacing and media coercivity have a strong impact on write width, but not on track edge erasure. On the other hand, media design does not impact transition curvature significantly. Experimental observations were supported by media micromagnetic modeling results and write field simulation using a finite element model. Analyzing the write bubble helps to understand the dependence of adjacent track encroachment on media design. Cross track profiles of various signal-to-noise ratio (SNR) components can provide valuable insights into different track edge mechanisms.
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