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Micromagnetic Modeling for Heat Assisted Magnetic Recording

Micromagnetic Modeling for Heat Assisted Magnetic Recording. Zhenghua Li 1 , Dan Wei 2 and Fulin Wei 3 1) Research Institute of Magnetic Materials, Lanzhou University LanZhou, Gansu 730000, China

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Micromagnetic Modeling for Heat Assisted Magnetic Recording

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  1. Micromagnetic Modeling for Heat Assisted Magnetic Recording Zhenghua Li1, Dan Wei2 and Fulin Wei3 1)Research Institute of Magnetic Materials, Lanzhou University LanZhou, Gansu 730000, China 2) Magnetic Physics Laboratory, School of Materials Science and Engineering, Tsinghua University, Beijing100084, China

  2. Contents 1.Introduction of HAMR Background Fundamental Problems 2.Theoretical Modeling Heat transfer model Laser Transmission in Metal Alloys 3.Simulation Parameters 4.Simulation Results 5.Conclusion

  3. KuV/kBT= 60 KuV/kBT= 35 Background Reduce grain size Superparamagnetism Chose high Ku materials 1Tb/in2

  4. Fundamental problems • A write field exceeding 17 kOe is not expected, even if the single- pole-trimmed (SPT) write head is perfectly designed and the SPT head is combined with perpendicular media that have a soft magnetic underlayer. • Heat assisted magnetic recording has the potential to enable data storage on media having extremely high values. • With this technique, one can use media with exceedingly high anisotropy fields, such as L10 FePt that has a thermally stable grain size smaller than 3 nm. Theoretically, such a small grain size could support areal densities well beyond 1 Tbit/in2.

  5. FePt L10(10 nm) MgO(5nm) Soft Under layer (130nm) Heat transfer model Top and bottom boundaries Other boundaries • q stands for the heat power of the laser beam (W/V) • is chosen as 10-13s. • The convection coefficienth is chosen as 10 W/m 2/K.

  6. Laser transmission in metal alloys

  7. 1.2 Main pole (Bs=2.4T) 40nm 40nm Materilas (Wm-1K-1) CV (106Jm-3K-1) Ms(300K) 1100(emu/cc) k FePt(10nm) y MgO(5nm) HK(300K) 80 KOe soft underlayer(130nm) Bs=2.0T FePt 10 4 A* 10-7 erg/cm Substrate MgO 5 3.6 grain diameter x 5nm z SUL 20 4.35 JOURNAL OF APPLIED PHYSICS VOLUME 91, NUMBER 10, 6595(2002). 0 770K Simulation Parameters Thermal parameters of the materials Temperature dependance of Ms and HK of FePt Alloy Magnetic Parameters of FePt

  8. Temperature evolution of the magnetic layer Cross Track direction Cooling process Laser heating (P=7.5 mW) (c) (a) (a) Temperature evolution of the local area (as seen in Figure (c)) during the heating and cooling process. (b) The instant temperature distribution and the laser intensity distribution of the magnetic layer.

  9. The y-component of the magnetization pattern in magnetic layer with different thermal contours T=732K T=755K T=713K T=722K The initial magnetization is set to be -1

  10. The y-component of the magnetization is shown after the application of a laser heating profile and a revised write field, HYmax=15Koe T=755K T=732K Main pole T=722K T=713K Both the medium and SPT head are stationary

  11. Written bit patterns of a single track in the HAMR System • Head-medium speed is 40m/s • Head-medium spacing is 5nm • The area density is beyond • 1Tb/in2 (a) Instant temperature distribution in the cross track direction, (b) Writing field distribution of the SPT head in the cross track direction, (c)(d) Written bit patterns of a single track in the HAMR system and the relationship with laser and main pole

  12. Conclusion • The written bit patterns of the magnetic layer are determined not only by the write head geometry, but by the way the media responds to temperature and the strength of the write head field. • the selection of the SUL material is crucial for the cooling process • The distance from laser to rear/front edge should be less than 41.4/1.4nm respectively, which is an important parameter for designing an integrated HAMR head.

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