Transcript 幻灯片 1 - University of Alabama

Micromagnetic Modeling for Heat
Assisted Magnetic Recording
Zhenghua Li1, Dan Wei 2 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
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
Background
Reduce grain size
KuV/kBT= 60
Superparamagnetism
KuV/kBT= 35
Chose high Ku materials
1Tb/in2
Fundamental problems
A write field exceeding 17 kOe is not expected, even if the singlepole-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.
Heat transfer model
 T  q  CV
2
FePt L10(10 nm)
MgO(5nm)
Soft Under layer
(130nm)

T
n
T
t
 h (T  T room )
T  T room
T | t  0  T room
Top
and
bottom
boundaries
Other
boundaries
 q stands for the heat power of the laser beam (W/V)
  t is chosen as 10-13s.
The convection coefficient h is chosen as 10 W/m 2/K.
Laser transmission in metal alloys
y
Simulation Parameters
40nm
Materilas
 (Wm-1K-1)
CV (106Jm-3K-1)
x
z
Main pole (Bs=2.4T)
40nm
FePt(10nm)
MgO(5nm)
soft underlayer (130nm)
FePt
MgO
SUL
10
4
5
3.6
20
4.35
Bs=2.0T
Substrate
1.2
Ms (T )
Ms ( 300 K )
HK (T )
HK ( 300 K )
Thermal parameters of the materials
Ms(300K)
1100(emu/cc)
HK(300K)
80 KOe
A*
10-7 erg/cm
grain diameter
5nm
Magnetic Parameters of FePt
JOURNAL OF APPLIED PHYSICS
VOLUME 91, NUMBER 10, 6595(2002).
0
770K
Temperature dependance of Ms and HK of FePt Alloy
Temperature evolution of the magnetic layer
Cross Track direction
800
150
750
700
Cooling process
100
650
600
Laser heating (P=7.5 mW)
550
50
500
450
0
(a)
(a) Temperature evolution of the local
area (as seen in Figure (c))
during the heating and cooling
process.
400
0
50
100
(c)
(b) The instant temperature distribution
and the laser intensity distribution of the
magnetic layer.
150
The y-component of the magnetization pattern in
magnetic layer with different thermal contours
150
0
150
0
-0.2
-0.2
100
100
T=755K
-0.4
-0.4
-0.6
50
-0.6
50
-0.8
-0.8
0
0
0
50
100
150
-1
0
50
100
150
0
0
-0.2
100
-0.2
100
-0.4
-0.4
-0.6
50
-0.6
50
-0.8
-0.8
0
0
50
100
150
-1
150
150
T=722K
T=732K
-1
0
0
50
100
150
-1
The initial magnetization is set to be -1
T=713K
The y-component of the magnetization is shown
after the application of a laser heating profile
and a revised write field, HYmax=15Koe
150
T=755K
0.5
100
0
50
-0.5
150
0.5
100
0
T=732K
50
-0.5
Main pole
0
0
50
100
150
150
-1
0.5
100
0
T=722K
0
0
50
100
150
150
-1
0.5
100
0
T=713K
50
0
-0.5
0
50
100
150
-1
50
0
-0.5
0
50
100
150
-1
Both the medium and SPT head are stationary
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
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.