Center for Materials for Information Technology A 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 Underlayers Soon-Cheon Byeon and Bill Doyle High speed switching in Perpendicular media Experimental V. G. Voznyuk and W. D. Doyle Theoretical Arko Misra and Pieter Visscher
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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.
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
– 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
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
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