Magnetic Data Storage
(1) Magnetic recording
(a) General (longitudinal recording)
(b) Thermal stability
(c) Advantage Media
Oriented longitudinal media
Anti-ferromagnetic coupling media
Pattern media and nano-particle media
High Ku medium (HAMR)
(2) Magneto-optical recording
(3) MRAM (STT RAM) and Flash disc
(4) RRAM and PRAM (Random Access Memory)
(5) Optical storage and other memory
Areal density progress in magnetic recording since its invention
(Moser et al. J.Phys D: Phys. 35(2002)R157-167)
Magnetic recording areal density growth along with transistor count per
integrated circuit device (McDaniel J. Phys: Condens. Matt. 17(2005)R315).
Areal density trends in HDD magnetic recording (Fujitsu
Sci. Tech. J., 42(2006)122).
Industry first 120 GB 2.5-in Seagate Momentus Ⅱ high capacity
mobile drive using TMR reading element (IEEE on Mag. 42(2006)97).
Schematic drawing of longitudinal recording system. B is the bit length, W is
the track width and t is the medium thickness. d is flying height of the head
abov the medium.
Schematic representation of longitudinal, digital magnetic
recording write process.
Transition width α (depends on Mrt / Hc)
(a) magnetization of two transition at x=0 and 200nm.
(b) magnetic field detected by read head, solid line is for longitudinal.
pw50 is shown for a read head with zero gap.
SNR≈0.31PW50BWread / α2d(1+σ2)
≈B2Wread / α2 d3 (1+ζ2)
B is bit length, Wread is read width of head, α is transition
parameter, d grain diameter, ζ normalized grain size
Recording Media Requirements
(1) for few particles per bit, the transition becomes less
sharp and pickup signal decreases. About 400 isolated
particles are required.
(2) Noise is due primarily to the formation of zigzag
transition between bits and this sawtooth pattern scales
roughly as Ms2/Ku1/2,
(3) the signal is proportional to the number of measured
events or particles per bit, N. Hence SNR ~ N1/2.
(4) the heads must approach to the hard disc surface.
Write head : having a sufficient high Ms so that the fringe field
exceeds the Hc of the medium (500-3000Oe); an
adequate magnetic permeability (easy saturated).
Read head: low Hc, low noise and extremely high permeability
in order to respond with a substantial change in flux
to the weak fringe field above the medium
Schematic M-H loop for ideal magnetic recording medium
and head material.
For write head: µ >>1, Ms large and Br=0;
For read head: µ >>1 , Hc = 0
Thin film recording head
Gap 200 nm.
Thin film recording head. Left, layout of pole pieces
and windings; right, enlarged, cross-sectional view
of magnetic pole pieces
Magnetoresistive read head (1980-90 from 10 -100 Mbit in-2)
h=1-2 µm, w=2-4 µm
Δρ/ρ =2.0% Ni81Fe19
Spin-Valve Read head
h=2-6 µ m and w=10 µ m
(1) SNR≈0.31PW50BWread /α2d(1+ζ2)
≈B2 Wread / α2 d3 (1+ζ2),
(2) Transition width α(depends on Mrt / Hc)
(3) Signal: small Mrt, large Hc, small distance
between head and disc, large GMR or TMR
(4) Areal density: decreasing the dimensions: B,
WRead, diameter of grain.
The develop of the magnetic recording
Before 1985: γFe2O3 medium, Ferrite ring head (～10Mbin-2)
1980: 1st thin film read head, continuous magnetic thin film with
high Hc, small α(25% CGR);
1990: 1st MR read head, decreasing thickness and, in turn, the
transition distance (80% CGR);
1997: 1st GMR read head (100% CGR);
2000: 1st AFM medium, increasing the effective volume.
2006: 1st TMR head for 80-100 Gbit in-2 longitudinal recording
In the physics of magnetic recording there are two key
factors in achieving very high areal density:
(1)The superparamagnetic effect (thermal stability);
(2)The finite sensitivity of the readback head.
In both cases, the limitations arise because the signal
energy becomes so small as to be comparable with
the ambient thermal energy.
The signal to media noise is approximately by the number
of magnetic grains (or switching units) per bit:
SNRmedia ~ Wbt / V
Where, wbt (bit volume, read-width x bit-length x thickness)
v (the grain volume)
In order to avoid thermal instability, a minimal stability ratio
of stored magnetic energy, KuV, to the thermal energy, KBT,
KuV/KBT ≌ 50 - 70
Oriented longitudinal media (Ku)
A favorable lattice matching
between CoPtCrB (1120)
Is parallel to CrX (002).
Toney et al., IEEE Trans. On Mag
A perfect orientation (large Ku) carries out:
(1) a low media noise
(2) a high signal level
(3) a smaller transition parameter
(4) a narrower switching field distribution
OR = Mr / Mr per >2.5 for current L media
mechanically texturing metal disk substrate
anisotropic etching of the substrate
directional deposition of the media
Oscillation Exchange Coupling
in Co/Ru/Co MLs
(Parkin PRL 64 (1990)2304).
Schematic illustration of (a) a two layered AFC media,
(b) LAC media with high J and (c) advanced three layers
LAC media for much lower Mr δ .
In the case of two layers AFC media
Mr t = Mr t1 – Mr t2
KuV1<KuVeff < (Ku V1+KuV2)
KuV/KBT ≌ 50 - 70
single layer media (a) and (b) an
AFC media, Jex=0.06 erg/cm2,
Fitted by Eq.(1)
(b) thermal decay at -500 reversal field.
Comparison of amplitude loss as aresult of thermal degration of
single layer media and AFC media
System parameters for estimating transition width and PW50
Design (AFC media) 60Gb in-2 200 Gb in -2
Bit length, B (nm) 38 27
Track width, W (nm) 280 115
Magnetic coecivity, Hc (Oe) 4000 5000
Mrt (memu/cm2) 0.32 0.2
Grain size (nm) 8.1 6
Head to media spacing (nm) 30 15
Shield to shield spacing, g(nm) 700 500
Transition parameter, a (nm) 12.8 6.2
Pulse width PW50 (nm) 99 54
User bit density (pw50/B) 2.6 2.11
IEEE on Mag. 39(2003)651 (Komag Inc.)
(1) Traditional longitudinal recording is approaching to
its limit (100 Gbit in-2 is achieved ).
(2) perpendicular recording offers about 421Gbit/in2
(Seagate demo) and 178.8Gbit/in2 (market).
(3) the next big challenge is 1 Tbit in-2 for recording
The possible models : pattern media; high Ku media
(HAMR); STT (Spin torque transfer) – RAM.
Schematic drawing of a perpendicular recording system
with SUL and a single pole head.
Advantages of PA recording:
a. high orientation ratio
b. lower media noise (α smaller)
c. increase of signal and thermal stability
d. writing field large
*Toshiba extends 2.5-inch mobile HDD Family with 200GB
market-leading capacity (178.8 Gb/in2) (May 2007 market),
*Fujitsu intros 250GB perpendicular drive (second quarter
*In the first half of 2007, Hitachi has brought hard drive areal
density halfway to the 345 Gbits/sq. in. market with the 1 TB,
3.5-inch (Deskstar 7K1000).
* Seagate 500GB for 2.5-inch (notebook), 2.5TB for 3.5 inch
desktop (41650 hours music, 800,000 photo, 4100 hours
digital video) to emerge in 2009. (Hitachi demo)
Perpendicular recording hard disc drive
PR recording using AF coupling media
1Tbit in-2 for 40nm period
Magnetic recording on a CoPd/Pd/CoPd dot array: (a) GMR readback signals
after dc magnetizing the sample (00) state and after applying a write pulse of
30 and 50 mA, creating, respectively, states (01) and (11);(b) SMRM image
Patterned media made by a focused ion beam
(a) topography image of the patterned area. P2 is write pole. (b) Magnetic
force microscopy image of a square wave pattern
Thermal stable, even if Ku is small; transition parameter
1 Tbit/in2 for patterned media
The islands are lithographically patterned into regular array
in the recording medium;
For 1 Tbit in-2, the island array periodicity is 25 nm and the
lithographic linewidth is ~12.5 nm for equal island and trench
The transitions must be precisely written between two
Nanoparticle media (self arrangements)
TEM image of a 3D assembly of FePt nanoparticles. Image size is 130nm x
130nm and particle diameter is 4nm.
Nanopartical media are made in a chemical process, then annealed to obtain
a hard magnetic phase.
HAMR AD = pδK / hNkBT
δ= 10nm, K=7x107 erg cm-3
h= KV/kBT= 60, T=330K, p=0.56
Lbit =2.64 nm(10-12 atoms)
cross-section of the bit, 60-80
volume 8 x 8x 50=3200 to
9 x 9x 50=4050 atoms
Given AD≈92 Tbin-2
Ultimate limit to thermally assisted magnetic recording
J Phys:C 17(2005)R315-332
(Solid immersion lens)
ZnS:SiO2 NA ~1.1
Media: Co69.48-xTb30.52Agx, x=0-25.68
Fujitsu paves way for 5TB hard drives (1Tbits/in2, 04/12/2006 demo
a spot size 88nm x60nm using HSRM)
SmCo has a Ku value about three times high FePtX,
and this might push AD estimate into 250-300 Tbin-2.
The entire printed contents of the United State Library
of Congress ( ~10Tb) could be stored on a 30 mm
diameter disk (50Tb/in2). This is about the size of
US fifty-cent coin.
θ k is defined as the main polarization plans is tilted over
a small angle;
εk = arctan(b/a).
(a) Assembly of apparatus
(b) Rotation of polarization
of reflecting light.
Principle of thermomagnetic recording (Curie point
writing): (a) before, (b) during and (c) after the writing.
From Oppeneer Magneto-optical Kerr spectra in Handerbook of magnetic
Materials, Edited by Buschow (Vol.13)
Experimental pola Kerr ritation an undoped MnBi sample (Di et al. 1992)
and Al-doped MnBi (Shang et al., 1997) sample at room temperature.
(Magnetic random access memories)
Schematically representation of MRAM structure and
M-H, ΔR/R characteristics of the PSV.
Schematic of the read and write processes in a PSV random access
Table: composition and dimensions of the principle layers in a current
representative MARM device.
Advantage of MRAM
(1) It combines the speed of SRAM with the non-volatility
(2) It also offers a low-power memory solution which
eventually may match DRAM’s capacity and density
(3) No limit for write-read cycles (flash 100,000)
7/2 2006 Toshiba and NEC, 16 megabit density, read write
speed 200 Mbytes/sec, operation at 1.8V, a chip 78.7 mm2;
9/6 basic technology for 256 Mbit
4Mbits MRAM enter in market (2007 March meeting). As
embedded memory in Automobiles, $20 for a half megabyte.
The MgO-based magnetic tunnel junction film
CoFeB/Ta. (Lee etal., IEEE Trans on Mag 43(2007)917).
Fig. 1.R–H loop in MgO-based MTJ. Fig. 2. Magnetoresistance versus variatio
current in MgO-based MTJ structures
using a current pulse width of 200 s.
Fig. 3. Read/write cycle test. Inset: Resistance
change over 110 cycles with a current pulse
width of 200 s.
100nmGaAs on (001) semi-insulating GaAs
(a) a 20 µm wide channel with three pairs of Hall
(b) a domain wall was prepared at the boundary
of regions 1 and 2, and its position after application
of a current pulse was monitored by RHall=VHall/l,
Hc1 >Hc3 >Hc2
Yamanouchi et al Natural 428(2004)539
minus Plus pulse 83K
At t=0, the domain wall is at the boundary
of regions 1 and 2; when a negative current
pulse is applied, M direction in region 2 is
initial state After I=-300 µA After I=+ 300 µA
MOKE images of sample A using 546 nm light at 80K.
The future of scalable STT-RAM as a universal embedded memory
By Farhad Tabrizi, Grandis, Inc. (02/21/2007)
Fig. 1. STT-RAM addresses each bit individually by flowing
current directly through the bit. Unintended writing errors
are completely eliminated.
Fig. 1. STT-RAM addresses each bit individually by flowing current
directly through the bit. Unintended writing errors are completely
Fig. 2a " Conventional MRAM cell. A magnetic field, generated
by the bit line, cladding, and write word line, is used to switch
between the "0" and "1" states.
Fig. 2b " STT-RAM cell. By eliminating the write word line,
bypass line and cladding, a STT-RAM cell is considerably
smaller than a conventional MRAM cell.
Fig. 2c " Total required current in STT-RAM continues to
scale lower with increasingly smaller geometries. Conversely,
conventional MRAM switching current increases with smaller
spin polarization along the axis
parallel to the vector ML of local
ferromagnetic polarization in will
be present in the electrons
impinging on MR.
S1,2 = (Ieg/c)S1,2 x (S1 x S2)
g = [ -4+(1+p)3(3+S1·S2)/4p3/2]
(J.C.Slonczwski 3M 159(1996)L1)
(C.Heide et al., PRB 63(2001) 064424).
NANORING for MRAM
Fig. 1. Plan-view and side-view scanning micrographs of a and b arrays
of Co circular rings, c NiFe/FeMn elliptical rings, d NiFe/Cu/Co elliptical
rings, and e and f NiFe/Cu/Co pseudo-spin-valve elliptical ring
device with six nonmagnetic contact wires.
Nanoring for MRAM
We have achieved nearly 100% vortex reversal in the asymmetric
nanorings, while the symmetric nanorings can accommodate only 40%.
(a) AAO (porous anodic aluminium oxide membranes), (b) 100 nm Fe film
by RF, (c) and (e) Fe nanoring in AAO pores.
SEM micrograph of the top view of the as –prepared AAO template.
The inset shows the oblique view of AAO showing the aligned nano-
Samsung offers flash disk as laptop upgrade
Report by Robinson in COMPuting, 22 May 2007
From the end of Jun, the 32GB SSD will be sold through
memory specialist just Rarm as part of its integral brand
For $350 ,
64GB model is due ship in the coming months
Competition Between Hard Disc and Flash Disc
Flash can be a potential replacement for hard disks
because of its high performance, noise free running, light
weight, fast data access and less power consumption.
iSuppli believes that by the fourth quarter of 2009, 24 million
Notebooks will be sold with some form of flash data storage,
compared to 143,600 in the first quarter of 2007.
That's nearly 60 per cent of anticipated laptop sales.
But the price factor is still the most active barrier.
Magnetic Hard Disc
Freecom Mobile HDD Drive 160GB USB-2, Release Date: Wednesday
2nd May 2007,Our Price: £78.95 ; LaCie 500GB USB 2.0 Hard Drive,
Release Date: Wednesday 20th September 2006, Our Price: £114.95
Seagate 500GB for 2.5-inch (notebook), 2.5TB for 3.5 inch
desktop (41650 hours music, 800,000 photo, 4100 hours
digital video) to emerge in 2009. (Hitachi demo)
Lui et al., APL 76(2000)2749
due to de-localization of localized valence electrons
by high electric fields (IEEE 2005).
Sharp Develops Basic Technology for RRAM,
Next-Generation Nonvolatile Memory
Dec 11 ,2006
A memory capable of programming data at rates about 100 times
faster than flash memory.
These results are the first step toward the practical use of this memory
technology. It will continue in the future aimed at bringing a commercially
viable product to market.
Philips claims 'super Flash' memory breakthrough
the 'phase-change' material changes phase from one to another using
pulses of electric current.
A doped Antimony Tellurium (SbTe) compound, unlike other attempts at
phase-change memory, well-suited to the standard CMOS process used to
make most computer chips.
The material's phase change is fast, taking place in under 30ns, in the
prototype cell. That is 100 to 200 times faster than today's Flash memory
cells, and getting awfully close to DRAM speeds.
Phase change vs Magneto-optics
Phase change 2001 next generation, 2003-2004
Products DVD-RAM UDO(1) nextGen DVD(2)
Capacity/surface, GB 4.7 20 25
No of surface 2 2 2/4
Bit area mm x mm 0.165x0.28 0.33x0.13 0.32x0.185
Transfer rate Mb/s 1.2 4-8 4-6
Products 3.5 in GIGMO(3) ID photo(4) 3.5 in GIG ID Photo
Capacity 2.3 0.73 10.0 3.0
No of surface 1 1 1 1
Bit area 0.67x0.233 0.6x0.235
Transfer rate 8.38 2.5 20+ 110
(1) SONY disc diameter=13 cm, (2) Matsushta prototype, two recording layers
(3) disc diameter=9cm, (4) disc diameter=5 cm.
Sony: 23GB, 11Mb/s (2003); 50GB, 22Mb/s (2005);100GB,43 MB/s (2007)
Two coherent beams are necessary.The one is an information b
including user data, the other is a reference beam. During the reco
process, they interfere with each other, and the interference patter
recorded in the media, called a hologram.
In the reconstructing process, the information beam can be reco
structed when the reference beam incident on the hologram.
(1) Longitudinal Recording
SNR ≈ B2 Wread / α2 d3 (1+ζ2),
Thermal stability KuV/KBT ≌ 50 – 70
(2) Perpendicular Recording
AD 421 Gbits/in2
(3) Advantage > 1Tbits/in2
Heat assisted magnetic recording
STT RAM (Nano-ring) FRAM
Super Flash (PRAM) FLASH (32Gbits)
(1) Magnetic Recording :Advancing into the future
A.Moser, K.Takano et al.,
J. Phys.D:Appl.Phys. 35(2002)R157-167.
(2) Longitudinal Magnetic Media Designs for 60-200Gb/in-2 Recording
Gerardo A. Bertero et al.,
IEEE Trans. on Mag. 39(2003)651.
(3) The limits to magnetic recording ---media consideration.
J of Magn. Magn. Matt. 200(1999)616-633.
(4) Recording on bit-patterned media at densities of 1Tb/in2 and beyond
H.J.Richter et al., IEEE Trans on Mag 42(2006)2255.
(5) Heat-assisted magnetic recording
R.E.Rottmayer et al., IEEE Trans on Mag 42(2006)2417.
(6) Magnetic bistability and controllable reversal of asymmetric ferromag-
F.Q.Zhu et al., PRL 96(2006)027205.
(7) Current-driven switching of magnetic layers
C.Heide et al., PRB 63(2001)064424
Takuo Tanaka and Satoshi Kawata
Three-Dimensional Multilayered Optical Memory Using
Two-Photon Induced Reduction of Au3+ Doped in PMMA
Akihiro Ohta, Masao Miyamoto, Yoshimasa Kawata, and Masahito
Multilayered Optical Memory for Terabyte Data Storage
(IEEE TRANSACTIONS ON MAGNETICS, VOL. 43, NO. 2, FEBRUARY 2007)
Ferroelectric Memories, March 2007
The traditional FeRAMs continue to be used in applications such as
smart cards and ID cards as well as targeting RFID, automotive and
space. Other ferroelectric memory devices such as organic polymer
ferroelectric FeFET memories are exciting new interest as well.
At least 10 companies continue to work on ferroelectric memories
for various applications such as fast, low power memory technology
for embedding in SoC. Several novel ferroelectric memory applications
have been discussed such as high density probe memory and
associative memory. Multi-bit FeRAMs have been shown which could
help with density and scaling issues.