perpendicular recording media
TRANSCRIPT
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
PERPENDICULAR RECORDING MEDIA Relaxation of Remanent Magnetization in Perpendicular Media
J.W. Harrell, Shoutao Wang, Scott Brown and Roy Chantrell**Seagate, Pittsburg, PA
Soft UnderlayersSoon-Cheon Byeon and Bill Doyle
High speed switching in Perpendicular mediaExperimental
V. G. Voznyuk and W. D. Doyle
TheoreticalArko Misra and Pieter Visscher
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Relaxation of Remanent Magnetization in Perpendicular Media
J.W. Harrell, Shoutao Wang, Scott Brown
Dept. of Physics & Astronomy
Center for Materials for Information Technology University of Alabama, Tuscaloosa, AL
Roy Chantrell
Seagate, Pittsburgh, PA
Support: NSF-MRSEC, MINT Center
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Magnetization decay• The thermal decay of the magnetization is a critical issue in
ultra-high density magnetic recording.
• The study of the relaxation of the remanent magnetization in zero applied field after partial demagnetization gives insight into the effect of interactions on the thermal stability.
E
G (E)
EC E
G (E)
EC
DC demagnetized
(DCD type)
AC demagnetized
(IRM type)
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Initial ZF viscosity in CoPtCrB film with perpendicular anisotropy
• Zero-field viscosity depends strongly on demagnetization state. Maximum S at ±Mrs.
-8
-4
0
4
8
-1 -0.5 0 0.5 1
IRM-typeDCD-type
S 0 (%/d
ec)
Mr
-12 -8 -4 0 4 8 12
perppara
M
H (kOe)
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Calculated ZF Viscosity for CoCrPtB ⊥ Media
Monte-Carlo method(no exchange)
Mean-field calculation: Nd = -0.47
(KV/kT = 55, H0 = 5 kOe, σV = 0.4)
-2
0
2
4
-1 -0.5 0 0.5 1
DCD type (C* = 0)IRM type (C* = 0)
S 0 (%/d
ec)
Mr0
-6-4-20246
-1 -0.5 0 0.5 1
DCD type IRM type
S0 (%
/dec
)M
r0
Mean field method
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Quasistatic calculation of demagnetization factor
Choose demag factor to construct ‘best’ log-normal switching field distribution from recoil curves: Nd = -0.40 (Nd = -0.47 from relaxation meas)
van de Veerdonk et al, IEEE Trans. Magn. 39, 590 (2003)
-600-400-200
0200400600
-1 104 -5000 0 5000 1 104
Nd = -0.40
Nd = 0
M (e
mu/
cc)
H (Oe)
-400-200
0200400
-1 104 -5000 0 5000 1 104
M (e
mu/
cc)
H (Oe)
Nd = -0.2
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Exchange stabilizes saturation remanence in perpendicular media
Monte-Carlo calculations
-6
-4
-2
0
2
4
6
-1 -0.5 0 0.5 1
S(%
/dec
)
Mr0
C* = 0
C* = 0.1
C* = 0.22
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Exchange interaction can dominate shape of relaxation curve in both perpendicular and longitudinal media
Longitudinal CoPtCrBPerpendicular Co/Pd
-2
-1
0
1
2
3
-1 -0.5 0 0.5 1
IRM-typeDCD-type
S 0 (%/d
ec)
Mr
-0.4-0.2
00.20.40.60.8
-1 -0.5 0 0.5 1
IRM-typeDCD-type
S0 (%
/dec
)
Mr
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Summary of effect of interactions on remanent relaxation
• No interactions – viscosity independent of MR over wide range.
-1 -0.5 0 0.5 1Ze
ro-F
ield
Vis
cosi
ty, S
0
Remanence Moment, Mr
• Exchange interactions –stabilizes saturation remanence, enhances decay of reduced remanence.
• Demagnetization field –destabilizes saturation remanence.
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Synthetic Antiferromagnetic Coupled Fe65Co35/Ru/Fe65Co35 Soft Underlayers
for Perpendicular Media
S. C. Byeon and W. D. Doyle
MINT CenterThe University of Alabama
This project was funded by INSIC.
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Historical Development of Soft UnderlayersTarget: 200 nm thick ferromagnetic layer and µ ~ 100
FeTaN/IrMn- G/FeTaN(20)/[IrMn(10)/FeTaN(20)]9
19 layers- High 4πMs ~ 20 kG- Thermal instability of FeTaN Fe10Co90/IrMn
- G/Cu/IrMn/[FeCo(50)/IrMn(10)]4/FeCoN(20)11 layers
- Low 4πMs 15 ~ 16 kG
Fe65Co35/IrMn- G/Cu/IrMn/[FeCo(50)/IrMn(10)]4/FeCo(25)
11 layers Not enough thermal stability
Increased Hk
Enhanced thermal stability
Increased 4πMs
Optimize seed layer
Fe65Co35/IrMn- G/Ta/Cu/IrMn/[FeCo(50)/IrMn(10)]4/FeCo(25)
12 layers Enough thermal stability
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Outstanding Hysteretic Properties in FeCo/IrMnMultilayer with Ta
G/Ta(20 nm)/Cu(20 nm)/IrMn(10 nm)/[FeCo(50 nm)/IrMn(10 nm)]4/FeCo(25 nm)
-100 -50 0 50 100
-1.0
-0.5
0.0
0.5
1.0
Hpo = 66 OeHeb = 38 OeHc, EA = 11 OeHc, HA = 1.7 Oe
m /
ms
H (Oe)
EA HA
Annealed at 225 oC in H = 500 Oe
-100 -50 0 50 100
-1.0
-0.5
0.0
0.5
1.0
TopFeCo
Hpo = 79 OeHeb = 49 OeHc,EA = 6 OeHc,HA = 1 Oe
m /
ms
H (Oe)
EA HA
As-deposited
The Ta underlayer maintained outstanding hysteretic properties.Annealing enhanced the single domain condition of Heb > Hc.
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Synthetic Antiferromagnetic Soft Underlayers
• Advantages
– Fe65Co35/Ru/Fe65Co35 with thick ferromagnetic layer– Better thermal stability than IrMn-based films– Ideal soft underlayers
• No edge demagnetization• Reduced number of layers• Improved efficiency for magnetic flux return
– Thinner spacer layer(~1 nm) than the 10 nm thick IrMn
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Expected film parameters• Fe65Co35/Ru/Fe65Co35 trilayer film parameters
– Saturation field (the field at which the moment has attained 85% of the saturation moment) Hs = 2JAF / MFtF (sandwich structure)
– Permeability µ=1+4πMs / Hs• JAF=0.82 erg/cm2, 4πMs=23 kG; Hs=230 Oe is required for µ =100• Fe65Co35 thickness = 47 nm (sandwich structure)
– (reference for JAF value: Huai et al., JAP, 85, 5528, 1999)
-1.0 -0.5 0.0 0.5 1.0
-1.0
-0.5
0.0
0.5
1.0
Mag
netiz
atio
n (A
rb. U
nit)
Applied Field (Arb. Unit)
EA HA
Glass/Ru 2.5 nm/FeCo (tF)/Ru (t)/FeCo (tF)/Ru 10 nm Ideal hysteresis loop
Easy axisZero remanenceGood separation of hysteresis
Hard axisClosed hysteresis loopInsensitivity of hysteresis loop to angle around hard axis
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Hysteresis of FeCo 50 nm/Ru 1 nm/FeCo 55 nm
100 -50 0 50 100H (Oe)
FeCo 55nm EA HA
-1.0 -0.5 0.0 0.5 1.0
-1.0
-0.5
0.0
0.5
1.0
Mag
netiz
atio
n (A
rb. U
nit)
Applied Field (Arb. Unit)
EA HA
– Experimental Ideal
Easy axis hysteresis loopGood separation of hysteresis
Hard axis hysteresis loopClosed hysteresis loop
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Angular Dependence of Hysteresis– FeCo 50 nm/Ru 1 nm/FeCo 55 nm
-100 -50 0 50 100
H (Oe)
-25o
-100 -50 0 50 100
H (Oe)
-15o
100 -50 0 50 100
H (Oe)
35o
100 -50 0 50 100
H (Oe)
-65o
-100 -50 0 50 100
H (Oe)
0o
-100 -50 0 50 100
H (Oe)
45o
-100 -50 0 50 100
H (Oe)
90o
-100 -50 0 50 100
H (Oe)
105o
-100 -50 0 50 100H (Oe)
115o
Well separated hysteresis loop around easy axisVery narrow hysteresis loop around hard axis (Hc = 3.5 Oe)Very large angular reversibility of magnetization around hard axis ( 60o )
-100 -50 0 50 100H (Oe)
15o
EA
HA
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Saturation Field and Coupling Coefficient
0 50 100 150 200
0
2000
4000
6000
8000
Satu
ratio
n fie
ld H
s (O
e)
FeCo thickness (nm)0 50 100 150 200
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Inte
rlaye
r cou
plin
g co
effic
ient
JAF
(erg
/cm
2 )FeCo thickness (nm)
Hs = 2JAF / MFtF
Hs decreases faster than 1/tF.JAF is constant above 10 nm FeCo thickness.
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Conclusions
• Synthetic antiferromagnetic soft underlayer looks promising.• Antiferromagnetic coupling
– Glass/Ru 2.5 nm/FeCo (tF)/Ru (t)/FeCo (tF)/Ru 10 nm• Ru (t) = 0.6 - 1.0 nm for FeCo (tF) = 5 - 200 nm• Saturation field = 25 – 6000 Oe• JAF is constant above 10 nm FeCo thickness.
– Glass/Ru 2.5 nm/FeCo 50 nm/Ru 1 nm/FeCo 55 nm/Ru 10 nm• Well separated hysteresis loop around easy axis• Very narrow hysteresis loop around hard axis ( Hc = 3.5 Oe )• Very large angular reversibility of magnetization around hard axis (
60o )• Permeability of µ = 200 is obtained.
– Can be decreased ( µ = 100 ) using multilayer or thinner FeCo layers
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Future Work
• Identify optimum configuration.• Measure permeability directly.• Model angular dependent hysteresis process.
– Why negative remanence?– Why perpendicular remanence?
• Test thermal stability.
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Simulation of artificial antiferromagnetsArkajyoti Misra and P. B. Visscher, Department of Physics and Astronomy
M2FeCoExperimentally, one sees negative
remanence at certain angles. We have examined a possible mechanism for negative remanence, involving a slight misalignment of the easy axes in the two ferromagnetic layers.
Ru
M1 FeCo
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Negative-remanence mechanismWhen H is decreased after saturation, the thin (green) layer moves toward its easy axis, which is closest to H. This forces (via the AF interaction) the thick layer to move the other way. At H=0, thecomponent of M1 along H exceeds that of M2.
EAthick
H
x
φ
θ
M1M2
EAthin
M-H Loopy
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
High speed switching in perpendicular media
V. G. Voznyuk and W. D. Doyle
Center for Materials for Information Technologyand Department of Physics,
University of Alabama
Supported by the NSF Grant No. ECS-0085340 and made use of the NSF MRSEC Shared Facilities Grant No. DMR-0213985
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Experimental Setup. Pulse Generation and Monitoring.
High Voltage DC Power Supply
Coaxial Cable RG-213
Spark Gap
Transient DigitizerSCD 1000
Microstrip Line AttenuatorsR
Trigger Unit
all interconnections made with coaxial RG213 type cables
Microstripline with perpendicular media cross-sectionMicrostripline interconnect design
Ground Plane
x
y
z
Kapton insulator
Sample under conductor
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Sample Structure and Magnetic Properties
5 nm20 nm1 nm4 nm400 nm7 nmCCo Pt12 Cr18 /CrTaNiAl/ /CoNb8Zr5 /NiGlass / Al /
Sample is provided through INSIC–EHDRM by Yoshihiro Ikeda, IBM Almaden Research CenterRecording layer (RL)
Hcr [100 s] = 4350 OeMst = 0.75 memu/cm2
Mr/Ms ~ 1
Soft Underlayer (SUL)
Mst = 34 memu/cm2
Hc < 0.1 Oe (10 Hz)
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
What is the actual field generated by the microstripline?Sample: Glass / NiAl [7nm] / CoNb8Zr5 [400nm] / NiAl [4nm] / CrTa [1nm] / Co Pt12 Cr18 [20nm] / C [5nm]
CZVH
0
=
10-11 10-9 10-7 10-5 10-3 10-1 101 1030
1000
2000
3000
4000
5000
6000
n=2/3 Sharrock fitH
0 = 6000 ± 200 Oe
KV/kT = 170 ± 20
HPS
HTD
MOKE long time data Sharrocks fit
Hcr
(Oe)
pulse width (s)
Z0- microstrip line characteristic impedance, C – calibration constant of themicrostip
HPS – field calculated from current distribution using a power supply voltage (VPS):
HTD – field calculated from amplitudes of pulses recorded on Transient Digitizer (VTD)
( )
−=
n
cr lntfln
KVkTHH
21 0
0f0 - thermal attempt frequency ~ 109 Hz, H0 - intrinsic switching field Sharrocks fit1:
1 P. J. Flanders, M. P. Sharrock, J. Appl. Phys. 62 (7), 2918, (1987)
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.740
45
50
55
60
outin
Z (O
hm)
time delay (ns)
microstripline
sample
Time domain reflectometry data
Modeling the Measured Impedance Characteristics of the Pulse System
( )1
10
−+
=ρ
ρZZ ρ - reflection coeffisient., Z0=50 Ohm
0 1 2 3 4 5 6
0.0
0.2
0.4
0.6
0.8
1.0
Tran
smis
sion
, ref
lect
ion
coef
ficie
nts
frequency (GHz)
Coaxial Cable Microstripline with cables measured measured simulation simulation
Frequency domain data
1/G (f)
Model
R (f) L
CZ0=56 Ohm Z0=55 Ohm Z0=56 Ohm
Z0=44 Ohm Z0=44 Ohm
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Simulation results.Voltage and current at different points. 2.5 ns pulse.
Transient Digitizer
SCD 1000
Microstrip Line AttenuatorsCoaxial Cable RG-213 RG-213
Pulse Generator
V0 VMS I0 IMSVTD ITD
0 5 1 0 1 5 2 0 2 5
02468
1 0
volta
ge (k
V)
t im e (n s )0 5 1 0 1 5 2 0 2 5
0
5 0
1 0 0
1 5 0
2 0 0
curr
ent (
A)
t im e (n s )
X 3626 X 3626
%.520
=IIMS%.88
0
=VVTD
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
The field on the microstripline is very close to HPS
10-10 10-8 10-6 10-4 10-2 100 102 1040
1000
2000
3000
4000
5000
6000
n=2/3 Sharrock fitH0 = 6000 ± 200 Oe KV/kT = 170 ± 20
HPS HTD corrected based on simulation MOKE long time data Sharrock fit
Hcr
(Oe)
pulse width (s)
10-9 10-75000
6000
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
ConclusionsThe electrical behavior of the pulse system was simulated with
PSPICE using the measured impedance characteristics
For this particular microstripline power supply voltage provides more accurate field values than those determined from the Transient Digitizer
Hcr[t] data with the corrected field values exhibit an increase at short times as expected
Future workIncorporate the spark-gap into the model
Measure Hcr[t] vs. the initial remanence
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Simulation of fast switching in perpendicular media
Arkajyoti Misra, P. B. Visscherand D. M. Apalkov
Department of Physics and AstronomyThe University of Alabama
Supported by NSF grants # ECS-008534 and DMR-0213985, and DOE grant # DE-FG02-98ER45714
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Objective
• Simulate experiments under way on fast switching in perpendicular recording media
• Initial simulations are on CoCrPt system with no soft underlayer; simulations with underlayer are under way
• Coercivity: 2.5 kOe
• Material parameters from experiment
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
160 nm
Simulated System
160 nmy
z
x
20 nm
Landau-Lifshitz simulation using periodic BC’s in x and y, random thermal field (T = 300K);
cell size in simulation ≈ grain size
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
02.0 kOe 2.9
)exp(0
0
==
=
k
k
Hk
Hkk
H
xHH
σ
σ
5.0 J/m 107
)exp(120
0
=×=
=−
A
A
A
xAA
σ
σ
07.02/12 =∆θ
kOe 02.84 =sMπ
Material parameters from hard axis loop
Log-normal distribution of anisotropy field:
(x is normally distributed with variance 1)
Similarly, exchange constant distribution:
Hard axis loop
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Pulsed Field and Magnetization Response
Experimental pulse profile
Trapezoidal fitRise Time = 0.71 ns = Fall Time
Rise Time = 0.71 ns = Fall Time
= 2.6 ns
)( ∞== tMM r
)0( == tMM rs
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Simulated Remanent Magnetization
ns 6.2=∆t
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Time dependent coercivity
Center for Materials for Information TechnologyA NSF Materials Research Science and Engineering Center
Spring Review 2003
Counter-intuitive effect of the initial remanenceExpect high initial M (relatively unswitched) to be harder to switch:
In fact, however, it switches more easily:
Possible explanation: High-M state has more demag energy, which when released into spin waves, heats the system and accelerates thermal switching.