Study of microstructure and magnetic properties of FePt-based Exchange Coupled Composite perpendicular recording media
Date Issued
2011
Date
2011
Author(s)
Ke, Jian-An
Abstract
Ordered L10-FePt has good thermal stability, however its coercivity is too high for recording head to write. Soft layer helps hard layer to rotate its magnetic moment in Exchange Coupled Composite (ECC) media, lowering the switching field of the media. Thus we choose ECC media as main subject in this work to investigate the magnetic properties of various type ECC media.
Single FePt layer with perpendicular anisotrpoy can be obtained by controlling argon pressure (PAr) during FePt deposition. When PAr =4 mtorr, 21 nm Fe58Pt42 was directly deposited on glass substrate. Excellent perpendicular magnetic anisotropy was observed after post-annealing: out-of-plane coercivity (Hc⊥) is 11.5 kOe and out-of-plane squareness (S⊥) is 0.88. Discussion will be split into two parts: bilayer and graded ECC media. The Hc⊥ of Glass/L10 Fe58Pt42 14nm/A1 Fe58Pt42 5 nm bilayer film is 9.5 kOe (20.3 kOe for single hard layer) and S⊥ is only 0.5. However, step-like behavior was observed in the M-H loop of this bilayer film. On the other hand, the Hc⊥ of H/S type graded ECC media is 10.8 kOe and S⊥ is 0.96. A trade-off between perpendicular anisotropy and switching field of ECC media could be observed.
Various film structure of ECC media was also investigated. We found that the switching field can be further decreased by introducing extra diffusion interfaces with fixed soft layer thickness. After annealing at 700℃ for 30 mins, the Hc⊥ of Glass/ Fe58Pt42 7 nm/ Fe40Pt60 5 nm/ Fe58Pt42 7 nm is further decreased to 7.9 kOe, and S⊥=0.955. On the other hand, the magnetic anisotropy is affected by the sequence of deposition of hard and soft layers: the perpendicular magnetic anisotropy is better when hard layer is deposited first.
Graded ECC meda with multiple diffusion interfaces is proposed as an effective method to decrease the switching field without degradation of perpendicular magnetic anisotrpy in this work. It is available for the application of high Ku material with low switching field in magnetic recording technology.
Subjects
perpendicular magnetic recording
exchange coupled composite media
Type
thesis
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