Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Thermal Effects in Magnetic Recording Media
J.W. Harrell
MINT Center and Dept. of Physics & Astronomy
University of Alabama
Work supported by NSF-MRSEC
MINT Fall Review, Nov. 2001
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Stability Problem in Granular Media
M M M
Higher densities:
⇒ smaller grain size
⇒ magnetization decay and time dependent coercivity
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Projects
• Zero-field relaxation (NSF-MRSEC) – Shoutao Wang
• Self-assembled L10 magnetic nanoparticles (NSF-MRSEC) – Dave Nikles, Shishou Kang, Shoutao Wang, Min Chen
• Relaxation in perpendicular media (Hitachi Maxell) – Scott Brown
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Zero-Field Relaxation Measurements
Measure decay of remanence at zero field after partial dc demagnetization.
Recently reported for longitudinal thin film media, granular films, and tapes.
(S. Wang)
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Zero Field Relaxation in Longitudinal Media
Relaxation curves for Fuji film (CoCrPtB) of 5 nm thickness (KV/kBT = 29).
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Zero Field Relaxation in Perpendicular Media
-6
-4
-2
0
2
4
6
-1 -0.5 0 0.5 1
measuredcalculated
S0 (
%/d
ec)
mr0
σ = 0.17KV/kT = 38α = -0.07
Fit Parameters:
h = H/Hk = happl+ αmr
σθ= σK=0, σV=0.17,
KV/kT = 38, α=-0.07
Note: (KV/kT)meas = 54 from HCR(t).
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Self-Assembled L10 FePt Nanoparticles
(a) Before annealing: d ~ 3.4 nm, disordered fcc, superparamagnetic
(b) After annealing above 500oC: high anisotropy L10 phase (ordered fct)
(S. Kang, S. Wang, M. Chen, D. Nikles)
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Preparation of FePt Nanoparticles *
(D. Nikles and M. Chen)Particle Synthesis
Reduction of platinum acetylacetonate with 1,2-hexadecanediol and decomposition of iron pentacarbonyl in octyl ether with oleic acid and oleyl amine.
Particle Purification by FractionationEthanol was used to precipitate the nanoparticles from octyl ether.Redisperse in hexanePrecipitate with ethanol
Self-Assembly into Two Dimensional Arrays1:1 mixture of hexane and octane were used to re-disperse the precipitated nanoparticlesPlace a drop on a coated Cu TEM grid (either carbon-coated or silicon oxide coated)Allow to slowly evaporate
* Modification of the procedures reported in S. Sun, C. B. Murray, D. Weller, L. Folks and A. Moser Science 2000, 287, 1989-1992
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
M-H Loops of L10 FePt Nanoparticles100
50
0
-50
M x1
0-6
(em
u)
-10 0 10H x10
3 (Oe)
DCD
FePt@500oC
60
40
20
0
-20
-40
-60
M x1
0-6
(em
u)
-10 0 10H x10
3 (Oe)
DCDFePt@520
oC
80
60
40
20
0
-20
-40
-60
-80
Mx1
0-6
(em
u)
-10 0 10Hx10
3 (Oe)
DCDFePt@550
oC
100
50
0
-50
-100
Mx1
0-6
(em
u)
-10 0 10Hx10
3 (Oe)
DCD
FePt @580oC
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Coercivity Ratio
1
1.2
1.4
1.6
1.8
2
2.2
2.4
0 0.2 0.4 0.6 0.8 1 1.2
3-D, α = 03-D, α = 0.23-D, α = -0.22-D, α = 0
HC
R/H
C
distribution width
Calculations:
• Log-normal distribution of anisotropy energies
• Mean-field interaction : h = happlied + αm
• No thermal effects
Large HCR/HC ratio in L10 FePt nanoparticles is related to large anisotropy distribution.
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Magnetic Relaxation in Perpendicular Media
1 10 100Time (s)
0
0.1
-0.1
-0.2(b.)
0
0.1
-0.1
0.2
-0.2(a.)
Mom
ent (
mem
u)
TbFeCo – better under-standing of nucleation and domain wall motion processes.
Co/Pd mutilayers – effect of seed layer, B addition, etc.
(S. Brown (MINT), Hitachi Maxell)TbFeCo
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Moke Magnetometer for Perpendicular Media
(Scott Brown)
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Future Work
Zero Field Relaxation:
- Additional measurements and modeling to understand the role of interactions.
Self-Assembled Nanoparticles:
- Reduction of ordering temperature
- Alignment of easy axes
- Origin of anisotropy distribution
Center for Materials for Information Technologyan NSF Materials Science and Engineering Center
Future Work (cont.)
Perpendicular Media:
- Continued investigation of TbFeCo system to better understand the reversal processes.
- Magnetization reversal in Co/Pd multilayers. Effect of seed layer, boron addition.
- Zero field relaxation.