Magnetic Data

Presented By:
Mohammad. Imran khan S.No : 20156471.
MAGNETIC DATA STORED ON MAGNETIC TAPE.
Asst. Prof. Dr. Salaheddin Sabri.

Overview.
 Introduction.
 History.
 Processing.
1.1 Processing of Magnetic Tape.
1.2 Processing route for particulate magnetic tape.
1.3 Data Stored on Magnetic Tape.
 Structure.
2.1 Structural Properties of Magnetic Tapes.

Overview.
 Properties.
3.1 Properties of Magnetic Tape.
3.2 Physical Properties of Magnetic Tape.
 Performance.
 Advantages and disadvantages of magnetic tape
 Conclusion.
 References.

INTRODUCTION.
“Magnetic storage or magnetic recording is the storage of data on a
magnetized medium. Magnetic storage uses different patterns of
magnetization in a magnetisable material to store data and is a
form of non-volatile memory. The information is accessed using
one or more read/write heads.”
Magnetic recording is a backbone technology of the electronic age. It
is a fundamental way for permanently storing information.

History of Magnetic Data Storage.
 Magnetic storage in the form of wire recording —audio recording on a
wire—was publicized by Oberlin Smith in the Sept 8, 1888 issue of
the Electrical World.
 The first publicly demonstrated (Paris Exposition of 1900) magnetic
recorder was invented by Valdemar Poulsen in 1898. Poulsen's device
recorded a signal on a ferromagnetic wire wrapped around a drum.
 However, the familiar Oxide tapes for audio recording were not developed
until 1947, by 3M Corporation.

History of Magnetic Data Storage.
 In 1928, Fritz Pfleumer developed the first magnetic tape recorder.
Early magnetic storage devices were designed to record analog audio
signals.
Fig No: 1 Fritz P fleumer.
 Computers and now most audio and video magnetic storage devices
record digital data.

 Transmission electron
micrograph showing the
microstructure of the
perpendicular magnetic
recording medium used in hard-
disk drives. (Fig No:2)
 Magnetic storage hard disks
used in laptop (left) and desktop
(right) computers.
 Inside of a hard disk drive.
 d) Laptop computer (Fig No:4)
Fig No: 2.
Fig No:3
Fig No:4

Generation magnetic field vacuum
• N = Total no of turns.
• L = length of each turn (m)
• I = Current (ampers)
• B = Magnetic field.
Created by current through coil
Generation of a Magnetic Field -- Vacuum I = current
(ampere) I B N = total number of turns = length of
each turn (m) B = magnetic field (tesla)
Fig No:5
Fig No:6

Generation of magnetic field with a solid material.
• B = Magnetic field ( Telsa)
inside the material.
A magnetic field is induced in the material.
Relative permeability (dimensionless)
Fig No:7

Origin of magnetic moments
• Net atomic magnetic moment :
--Sum of moments from all electrons.
Four type of responses..
Magnetic moments arise form electron motions and the spins on
electrons.
Fig No:8

Types of Magnetism
Graph No: 1

Magnetic responses for four types
Fig No : 9 Magnetic Responses.

Influence of temperature on Magnetic Behavior.
With increasing temperature , the saturation magnetization
diminishes and then abruptly drop to zero at curie Temperature.
Graph No:2 Influence of Temperature.

Domains in ferromagnetic & ferrimagnetic materials
As the applied field (H) increases the magnetic domains change shape and
size by moment of domain boundaries.
Graph No:3 Domains in
types of magnetic
materials.

Hysteresis and Permanent Magnetization.
Graph No: 4

Magnetic Anisotropy
Easy Magnetizing direction : Ni-[111], Fe-[100],
Co-[001]
Hard Magnetizing direction : Ni-[100], Fe-
[111], Co-[1120]
Graph No:5
Graph No: 6

Hard and soft Magnetic materials.
Hard Magnetic Materials:
-Large Coercivities
-Used for large magnets.
-add particles/voids to inhabit domain wall
motion.
-Example: tungsten steel
Hc = 5900 amp-turn/m
Soft Magnetic materials:
-Small coercivities
-used for electric motors.
-example: Commercial iron 99.95 Fe
Graph No: 7

Designing Process.
 Magnetic Emulsions
The recording medium for the
tape recording process is typically made
by embedding tiny magnetic oxide
particles in a plastic binder on a polyester
film tape.
Iron oxide has been the most widely used
oxide, leading to the common statement
that we record on a "ribbon of rust". But
chromium oxide and metal particles
provide a better signal-to-noise ratio and a
wider dynamic range.
Fig No: 10

Designing Process.
 The oxide particles are on the
order of 0.5 micrometers in size
and the polyester tape backing
may be as thin as .01 mm. The
oxide particles themselves do not
move during recording. Rather
their magnetic domains are
reoriented by the magnetic field
from the tape head.
Fig No: 11

Designing Process.
• The data is stored in the form of tiny segments of magnetized and
demagnetized portion on the surface of the material. Magnetized
portion of the surface refers to bit value ‘1’ were as demagnetized
portion refers to ‘0’.
• The major difference between magnetic tape units are the speed at
which the tape is moved past the read/write head and the density
of the recorded information. The amount of data or the number of
binary digits that can be stored on a linear inch of tape is know as
tape’s recording density.

Processing route for particulate magnetic tape.
 The magnetic particles are mixed with a binder (dissolved in a
solvent), lubricants that will help reduce the friction when then
tape is moved over the head and abrasives (such as Al2O3) that are
hard and help prevent wear of the magnetic tape.
 This mixture is poured onto a PET (polyethylene tetraphtalate)
substrate, which is ~25mm thick. Sometimes aramid substrates are
used for a long play cassettes, as these substrates can be as thin as
5 mm.

 The Particles are magnetically anisotropic, usually due to their
shapes, and the next stage of the process is to align these particles
in the length of the tape while the magnetic layer is still liquid.
 The solvent is then evaporated by heating the tape and it is rolled
to improve the density and leave a magnetic layer of about 3-5mm
thick.

• During manufacture, these particles are aligned such that this
direction parallels the direction of motion of the tape past the
write head. In as much as each particle is single domain that may
be magnetized only in one direction or its opposite by the write
head, two magnetic states are possible.
• These two states allow for the storage of information in digital
form, as ones and zeros.
• Using the plate-shaped barium-ferrite medium, a tape-storage
density of 6.7 Gbit/in2 has been achieved.

12

Writing & Reading Data.
Fig No : 13

Designing Process.
A video Showing the process of magnetic tape.

Process of Read & Write.
 Writing of data is performed using an inductive head, as
illustrated in figure .Reading of data also uses an inductive head or
,as in modern hard disk drives, a giant magneto resistive (GMR)
head (Illustrated in figure).
 The writing process involves passing a current (i.e. the signal to be
recorded) through the coil of the head .This current generates a
field in the air gap of the c-shaped core and a fringing field (in
the plane of the tape or disk) that extends out of the gap to the
tape or disk that is moving past it.

Process of Read & Write.
 The fringing field will change the magnetic state of the media and
if the magnetic properties of the media are appropriate then the
remanence of the tape in that region will be proportional to the
amount of current applied to the coil. for digital signals only two
remnant states are required for the material and hence the
material requirements are not as stringent as for analogue
recording, although smaller particles size is desired for high
storage capacity and faster access time.

Process of Magnetic Tapes.
• The reading process when carried out with an inductive head is very
similar to the writing process. The magnetic fields extending out the
tape or disk induce a field in the C-shaped core of the read head,
which in turn generates a voltage in the coil. This voltage can then be
turned back into the signal, be it audio, visual or digital data.
• The GMR elements shown in Figure is a spin value type with 4 layers:
an antiferromagnetic exchange film (e.g. Iron/manganese); a layer of
cobalt with its direction of magnetization pinned by the
antiferromagnetic exchange film (upwards as shown in fig); a layer of
copper which is a spacer and a layer of nickel/iron with its direction of
magnetization free to move under the influence of the magnetic field
from the recording media.

Structural arrangement of Magnetic Tapes.
 The storage layer is composed of granular media-a thin film (15-
20 nm thick) consisting of very small (~10-nm diameter) and
isolated grains of a HCP cobalt-chromium alloy that are
magnetically anisotropic.
Fig No:14

Structural Arrangement of Magnetic Tapes.
 The above figure is a transmission electron micrograph that shows the
grain structure of an HDD storage layer. Each grain is a single domain
that is oriented with its c-axis (i.e.,[0001] crystallo graphic direction)
perpendicular ( or nearly perpendicular) to the disk surface.
 Reliable storage of data requires that each bit written on the disk
encompasses approximately 100 grains. Furthermore, there is a lower
limit to grain size; for grain sizes below this limit, there is the
possibility that the direction of magnetization will spontaneously
reverse because of the effect of thermal agitation which causes a loss of
stored data.
 The current storage capacities of perpendicular HDDs are in excess of
100 Gbit/in2 (1011 bit/in2); the ultimate goal for HDD is a storage
capacity of 1 Tbit/in2. (1012 bit/in2)

 There is a range of magnetic particulates that can be used for tapes
and these are listed in below table with their magnetic properties.
The values of coercivity quoted in the below table are approx
average as the coecivity is highly dependent on particle size and
shape, which will vary in any batch of power.

Material
Saturation
Polarisation
(mT)
Intrinsic
corecivity
(kAm -1)
Average
Particle size Particle shape.
Y-Fe2O3 440 30 0.5 x 0.1 Needle
Co modified Y-
Fe2o3 460 60 0.5 x 0.1 Needle
CrO2 600 70 0.4 x 0.05 Needle
Fe 2100 125 0.15 x 0.05 Needle
BaO6Fe2O3 460 200 0.15 x 0.05 Disc
Table No : 1 showing approximate magnetic properties of particulates used in
recording media.

Properties of magnetic tape
Property Notes
Type of storage Magnetic
Data access Serial access (unlike the direct access of
a hard disk)
Cost of storage
This is probably the most cost effective
method of storing data which is why it
is the technology choice for archiving
data.
Capacity Can be a Terabyte or more
Speed
The slowest of all of the storage media
from which to access data, which is
why it is fine for archiving but not for
immediate data retrieval.

Properties of magnetic tape.
Portability
The magnetic tape itself is fairly small and
would fit into a pocket or bag. However, in
order to be read, an external tape drive is
required. Thus, this form of storage is not
considered to be very portable.
Durability
Although data can be saved to and erased
from the tape many times, each tape does
have a limited life span and eventually the
quality of the data storage will decline.
However if a tape is only used once for
archiving, then it will last many years,
typically 15 years. But of course you also need
to keep the tape reading equipment that can
read back the data for that time as well.
Needs to be protected from extremes of heat.
Reliability As long as it is not damaged, a magnetic tape
is very reliable method of data storage.

PHYSICAL PROPERTIES OF MAGNETIC TAPE
• Magnetic tape comes in a variety of widths and lengths. It
maybe contained in one of three categories of storage media:
industry standard open reels ,cartridges, or cassettes. The Figure
below shows the different categories of magnetic tape media.
• MAGNETIC TAPE CONSTRUCTION :Three basic materials are
used to make magnetic tape. They are: The base material A
coating of magnetic oxide particles

Figure No: 15 - Magnetic tape construction

A glue that binds the oxide particles to the base material figure
above illustrates the basic construction of a magnetic tape.
 Base Material. The base material for magnetic tape is made of either plastic
or metal. Plastic tape is more common because it is very flexible, resists
mildew and fungus ,and is very stable at high temperatures and humidity .
 Oxide Coating Oxide particles that can be easily magnetized(ferrous) are
coated onto the base material. The most common oxide materials are gamma
ferric oxide and chromium dioxide. It is very important that the oxide
particles are uniform in size and shape. If they are not ,the tape’s surface will
be abrasive and might damage the tape unit’s head.

Glue The glue used to bond the oxide to the base is usually an organic resin.
It must be strong enough to hold the oxide in place, yet flexible enough not to
peel or crack.
MAGNETIC TAPE HANDLING PROCEDURES
Magnetic tape handling procedures include the storage, handling,
maintenance, and control of tapes.

MAGNETIC TAPE PERFORMANCE
Fig No: 16

Performance of magnetic tape.
Machine Performance
To obtain more data on machine and tape performance, a test procedure was
devised which duplicated almost exactly machine operating conditions.
 Records were written consisting of 100 groups of bits, with a spacing between
groups of 0.010 inch.
 The number of records per tape varied depending upon the test desired, and
the inter-record space was adjusted for 1 inch.
 Each tape contained 5,000 records. During reading, the test
equipment checked each group of bits recorded on the tape. In addition, the
tape stopped between records for approximately 1 millisecond and then
accelerated back to the standard 72-inches-persecond speed.
 If any errors were present, the tape was automatically stopped ,and the portion
of tape containing the error was inspected.

Fig No: 17

The table shows the percentages of different types of identified
defects as obtained under the conditions described, which
represented a total tape operating time of 167 hours. Splices were
not necessary but were introduced primarily to test the improved
splice under typical machine start-stop and wear conditions.
During the same period of time, five errors were attributed
directly to the machine. These consisted of tube failures, part
breakages, and one case of power failure.

Maximum tape life is difficult to estimate. Tests on short lengths of
tape, that is, a 100-group record, indicate that over 100,000 passes
may be read, error free. In this series of tests the tape was read first
in one direction and then in the other. Longer lengths of tape do
not yield as many error-free passes. As an example, the best results
obtained with a 300,OOO-record tape showed only 356 consecutive
error-free passes.

The error terminating this run was caused by an accumulation of
white powder on the tape. After brushing off the powder, the tape
ran an additional 144 passes with only one error, an oxide particle.
After 500 passes, the test was terminated for other reasons. The
maximum tape unit machine operating time without error, neglecting
tape errors, was approximately 528 hours.

Advantages and disadvantages of magnetic tape
Advantages of magnetic tape Disadvantages of magnetic tape
Probably the cheapest form of storage
per megabyte of storage
Serial access so can be quite slow to
access data
Can store large amounts of data - up
to 1 Terabyte per tape cartridge
Need a special piece of equipment to
record and read the data on the tape
Can be set up to do the back up
overnight or over the weekend
The data may be corrupted if the tape
is placed near a strong magnetic field
e.g. a large speaker or magnet

References.
 http://hyperphysics.phy-astr.gsu.edu/hbase/audio/tape2.html
 https://en.wikipedia.org/wiki/Magnetic_storage
 http://study.com/academy/lesson/magnetic-storage-definition-
devices-examples.html
 http://www.igcseict.info/theory/3/mag/
 https://www.youtube.com/watch?v=f3BNHhfTsvk
 http://whatis.techtarget.com/definition/magnetic-storage
 Oxford university press Inc. Elements of Electro Magnetics.
 Physics for scientists and engineers with modern physics, fourth
edition.

Magnetic Data

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