john m. wiest duane johnson, alan lane, dave nikles, · magnetic layer 150 nm under layer 1.5 µm...
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THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Flexible Media Research
John M. Wiest
for
Duane Johnson, Alan Lane, Dave Nikles, Shane Street, Gary Mankey
and
K. Vemuru, M. Piao, B. He, L. Dong, H. Bagaria, D. Vickery, A. Bhandar
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Magnetic Tape
TEM Cross-sections of DLT IV Tape
Made by a double slot-die coating process:
Magnetic layer 150 nm
Under layer 1.5 µm
Base film 6.8 µm
Back coat 500 nm
The magnetic layer contains iron particles oriented parallel to the length of the tape
Hc ~1,800 Oe
Mrδ 7 to 8 memu/cm2
SQ 0.76 to 0.81
The under layer contains TiO2 or α-Fe2O3 particles
The back coat contains carbon black for anti-static
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Magnetic tape remains the primary medium for archival data storage.
However, the future of magnetic tape relies on a continuing rate of increase in data density while maintaining the current (or better) competitive advantage in cost.
The current limiting factors are track density,bit density, and tape thickness.
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
INSIC Magnetic Tape Storage Roadmap
2001 2006 2011
Track density (tpi) 900 2,700 9,800
Bit density (kbpi) 125 250 500
Tape Thickness (µm) 8.8 5.3 3.8
Length (m) 600 1,000 1,400
Areal Density (Gb/in2) 0.11 0.68 4.9
Volumetric Density (TB/in3) 0.03 0.3 3
Tape cartridge capacity (TB) 0.10 1 10
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Particulate Magnetic Tape in the Year 2015
Data cartridges with storage capacities approaching 100 terabytes -more than 20 TB/in3
Particle sizes less than 40 nm with polydispersity less than 5%
Highly ordered, self-assembled particles with particle volume fractions exceeding 50%
Magnetic film thickness less than 50 nm
New particles, beyond iron
Base films with thickness of one micron or less
Solventless coating processes that eliminate air pollution
Sustainable manufacturing and materials packages
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Track density and bit density are limited by noise.
Need thinner, smoother, more ordered magnetic layer containing smaller particles.
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Heart of the Matter: Dispersions of Magnetic Particles
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Heart of the Matter: Dispersions of Magnetic Particles
Cartoon
Reality
• Reverse micelle / association colloid templates to synthesize monodisperse particles.
• Block co-polymer nanoreactors to synthesize monodisperse particles
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Interdendrimer Magnetic Nanoparticles
Monodisperse, acicular,metallic Cobalt nanoparticles obtained in aqueous media by photochemical reduction in the presence of dendrimer.
-5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 5000-1.0x10-5
-5.0x10-6
0.0
5.0x10-6
1.0x10-5
HC = 300.6Oe
M (e
mu)
H (Oe)
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Dispersion/Oxidation Problems
“Ideal” “Reality”
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Pre-dispersed/Pre-protected Particles
Oxide Oxide
Metal Metal
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Dispersion CharacterizationProbes the particle moments in an AC field with a perpendicular DC field.
– DC field amplitude sweep– Transient response to DC field– AC frequency sweep– AC field amplitude sweep– Drying over time– Gelling over time
AC
Sus
cept
ibili
ty
0
4
8
1.E+1 1.E+2 1.E+3 1.E+4
ω (Hz)
χ 0
0
2
1 4 7χ'
χ''
χ'
χ"
Rhe
olog
y
Steady Shear Flow Small Amplitude Oscillatory Shear
1
10
100
0.01 0.1 1 10 100
ω (s-1)
G"
(Pa)
10
100
1000
0.01 0.1 1 10 100
ω (s-1)
G' (
Pa)
0.1
1
10
100
1000
10000
100000
0.0001 0.001 0.01 0.1 1 10 100 1000
γ (s-1)
η (P
a s)
.
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Dispersion Characterization
Shear thinning in viscosity a consequence of network reformation time being greater than characteristic time of flow.
The network is weaker, but re-forms more rapidly, at lower particle volume fractions.
Using rheology to probe structure
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0.01 0.1 1 10 100 1000
10/s1/s0.1/s0.01/s
t(s)
Ý γ 0
φ = 0.044
Normal Stress Growth
0.01
0.1
1
10
100
1000
10000
100000
0.001 0.01 0.1 1 10 100 1000
MP4.8MP4.4MP3.9MP3.2
Ý γ (s-1)
Viscosity
time
stra
in
Creep-Recovery
?
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Order and Self-Assembly
Order Parameter:s = 9
2tr(S ⋅S ⋅S)3S = uu−
13
δ
S = 1 : perfect prolate order S = -1/2 : perfect oblate order
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Order and Self-Assembly — Model
10-6 10-4 10-2 100 102
100
102
104
][ 1−sγ&
η[P
a s]S
Hγ&
Assume:• Anisotropic Hydrodynamic Drag• Maier-Saupe Steric Interaction• Magnetic Mean Field
Evolution of S:∂S∂t
+ v ⋅∇S = ....
Stress:τ = ...
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Order and Self-Assembly — Model
Need to incorporate:
• Polydispersity• Variable Magnetic Moments• Better Mean Field Potentials• Spatial Inhomogeneity• Equilibrium Network Structure
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Cryo-VSM: Angular Dependence of Remanence
Orientation Distribution
-1
-0.5
0
0.5
1
1.5
2
0 40 80 120 160
Ms (memu)Mp (memu)Mt (memu)
Rem
anen
ce (m
emu)
Angle (degrees)
Angular dependence of parallel remanence (Mp) and transverse remanence (Mt)
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Cryo-VSM: Angular Dependence of Remanence
f (θ ) =(Mp + ∂Mt
∂θ)2
0
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60 80 100 120 140 160 180Angle (Degrees)
“Calculating orientation distributions in magnetic tapes” J. W. Harrell, Y. Yu, Y. Ye, J. P. Parakka, D. E. Nikles, H. G. Zolla J. Appl. Phys. 1997, 81(8) 3800.
0 50 100 150 200 250 300 350 400 450 500Applied Field (Oe)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Ord
er P
aram
eter
(S)
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Small Angle Neutron Scattering in Shear and Magnetic Field(with Gary Mankey)
Measurements made at the Center for Neutron Research at NIST
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Model PredictionsSANS Data
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
SANS of Ferro/Nonmagnetic Dispersions in Shear Flow
Ferromagnetic Particles• Application of magnetic field perpendicular to
shear flow alters the orientational ordering.• Mixtures of F/NM particles will be studied to
extract the relative strengths of magnetic interactions on orientational ordering.
Shear
Fiel
d
Ferromagnetic Nonmagnetic
Ref: Poster by V.V. Krishnamurthy et al.
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Co-axial Shear Magnetometry
Measure susceptibility in flowing dispersion (with or without constant magnetic field in flow direction) toinfer order parameter.
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Coating Simulation Coating Stability
Goal: Thinner, Smoother Magnetic Layer
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Tape CharacterizationParticle Orientation Distribution
Angle
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Tape CharacterizationOrientation Distributions in Fuji Ultrium LTO Tape
0
0.2
0.4
0.6
0.8
1
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
f =
(Mp +
dM
t/dφ)
/2Angle (radians)
-1
-0.5
0
0.5
1
1.5
2
0 40 80 120 160
Ms (memu)Mp (memu)Mt (memu)
Rem
anen
ce (m
emu)
Angle (degrees)
Angular dependence of parallel remanence (Mp) and transverse remanence (Mt)
Orientation Distribution
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Tape CharacterizationSummary of Results for DLT IV Tapes
Sample Hc (Oe) SQ Mrt (memu/cm2) SUA-DLT IV-001
1 1768 0.779 7.61 0.6432 1835 0.785 7.62 0.639
UA-DLT IV-0031 1826 0.753 7.21 0.6272 1894 0.764 7.11 0.5953 1864 0.828 6.17 0.581
UA-DLT IV-0041 1746 0.817 7.98 0.6732 1813 0.810 7.75 0.6573 1779 0.818 8.03 0.663
A lot of room for improvement!
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Dimensional Stability
Thinner, smoother tape composed of smaller, better oriented particles must be able to with-stand increasingly demanding conditions in drives and libraries — without loosing (literally) the data.
Stretch-restretch for UA-DLT IV-001
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
0 0.01 0.02 0.03 0.04 0.05Strain
first stretchsecond stretch
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Mechanical Behavior of Magnetic Tape
Thinner, smoother tape composed of smaller, better oriented particles must be able withstand increasingly demanding conditions in drives and libraries.
This requires understanding the mechanical properties of the tape and how those properties are influenced by the materials package — the constitutive behavior of the tape and how it depends on tape structure.
Particle Order
π − pδ = 23
G − K
trγ [0]( )δ − Gγ [0]
−G1S: γ [0] S +13
δ
+ G3
N + B − 3( )S+ G N + B( ) S ⋅S− S : S S + 13
δ
Constitutive Relations
LTO
0
50
100
150
200
250
300
350
400
450
0 20 40 60 80 100 120time (sec)
0.1 mm/min
1 mm/min
5 mm/min
Tape Guiding,Wear, & Aging
Studies
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
GMR Heads
Thinner, smoother, more ordered magnetic layers reduce noise, but they also result in smaller signal.
Low noise does no good if you lose the signal, too!
Challenge for tape drive designers is how to implement GMR heads
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
GMR Heads Require GMR Friendly Tape
In addition to thinner, smoother, more ordered magnetic layer
GMR head issues for tape:
• Corrosion (binder chemistry)
• Thermal stability
• Electrostatic Discharge
• Head wear
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
New Binder Polymers• Polymers must prevent particle flocculation in dispersions.
• Polymers must protect particles against corrosion.
• Polymers must not corrode head materials (eliminate PVC, a source of inorganic chloride that may corrode the heads).
• Binder thermal properties will be more important (increase Tgto resist deformation due to hot GMR heats).
Amine-Quinone Polyurethane with Acrylate Groups in the Side ChainSr # POLYURETHANES HO-R-OH Mn
1 AQPUDA-1
(PEG 400)
400
2 AQPUDA-2
(Terathane 650)
650
3 AQPUDA-3
(Polycaproactone diol)
1250
4 AQPUDA-4 404
HO(CH2CH2O)nH
HO(CH2CH2CH2CH2O)nH
H[(OCH2)5C(=O)]nOCH2CH2OCH2CH2O[C(=O)(CH2)5O]nH
(OCH2CH2)nOHHO(CH2CH2O)n
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Tape Thermal Study
Cold tape does not like hot (e.g., GMR) heads!
ρ ˆ C p∂T∂t
+ v ⋅∇T
= −∇ ⋅q
q = −
κ magnetic
κ undercoat
κ substrate
κ backcoat
⋅∇T
Models for Layer ThermalConductivity Tensors Temperature in Tape
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
Some ‘Crazy Ideas’
• Self-assembled acicular particle arrays(requires monodisperse particles).
• Eliminate milling (pre-dispersed particles).
• There’s a lot of room in the undercoat — use it! (e.g., mechanical properties, heat management)
• Do away with the substrate (simultaneous coating of substrate monomer).
• Do away with the solvent (solvent = binder monomer).
• Self-assemble FePt nanoparticles on a flexible substrate.
THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGYAn NSF Science and Engineering Center
A ‘Crazy’ Idea: Self-assemble FePt nanoparticles on a flexible substrate
(FePt)80Au20
Ferromagnetic FePt Nanoparticles After Heat-treatment at 500°C for 60 min in a pressure reactor
-2 10-4
-1 10-4
0 100
1 10-4
2 10-4
-20 -15 -10 -5 0 5 10 15 20
Mag
netiz
atio
n
Magnetic Field (kOe)0
50
100
150
200
20 25 30 35 40 45 50 55 60
Inte
nsity
(cou
nts)
2θ
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