RECORDING HEAD TECHNOLOGY BASIC School of Mechanical Engineering Institute of Engineering Suranaree...

RECORDING HEAD TECHNOLOGY BASIC

School of Mechanical Engineering

Institute of Engineering

Suranaree University of Technology

Outline Magnetic and Magnetism History of Magnetic Recording Digital Data Encoding and Decoding HDD Write Head Technology HDD Read Head and MR Technology HDD Recording Material Introduction to Head Fabrications Introduction to HDD Head Test

HDD Component

HDD Recording Head

Magnetism Magnetism is one of the phenomena by

which materials exert an attractive or repulsive forces on other materials.

Some well known materials that exhibit easily detectable magnetic properties are nickel, iron, some steels, and the mineral magnetite.

Magnetism The ancient Greeks, originally those near

the city of Magnesia, and also the early Chinese knew about strange and rare stones with the power to attract iron.

Chinese found that a steel needle stroked with such a "lodestone" became "magnetic" when freely suspended, pointed north-south.

Around 1600 William Gilbert, proposed an explanation: the Earth itself was a giant magnet, with its magnetic poles some distance away from its geographic ones

Lodestone

Magnetism Until 1821, only one kind of magnetism was

known, the one produced by iron magnets. Hans Christian Oersted noticed that the current

caused a nearby compass needle to move. Andre-Marie Ampere, who concluded that the

nature of magnetism was quite different from what everyone had believed.

It was basically a force between electric currents: two parallel currents in the same direction attract, in opposite directions repel.

Magnetic Dipoles Normally, magnetic fields are seen as

dipoles, having a "South pole" and a "North pole";

A magnetic field contains energy, and physical systems stabilize into the configuration with the lowest energy.

The magnetic energy, so-called “flux” flows from the north pole to the south pole.

Magnetic Dipoles Magnetic dipoles result on the atomic scale

from the two kinds of movement of electrons.

First: the orbital motion of the electron around the nucleus.

Second: source of electronic magnetic moment is due to a quantum mechanical property called the “spin dipole” magnetic moment

Magnetic Field

Type of Magnet

Permanent Magnets Electromagnets

Permanent magnets A few elements -- especially iron, cobalt, and

nickel -- are ferromagnetic at room temperature. Every ferromagnetic has its own individual

temperature, called the Curie temperature, or Curie point,

A long bar magnet has a north pole at one end and a south pole at the other. Near either end the magnetic field falls off inversely with the square of the distance from that pole.

For a magnet of any shape, at distances large compared to its size, the strength of the magnetic field falls off inversely with the cube of the distance from the magnet's centre.

Classification of Magnetic Materials

Diamagnetism Paramagnetism Ferromagnetism Antiferromagnetism Ferrimagnetism

Diamagnetism In a diamagnetic material the atoms have no net

magnetic moment when there is no applied field. Under the applied field (H) the spinning

electrons produces a magnetisation (M) in the opposite direction to that of the applied field

Paramagnetism In paramagnetism materials each atom

has a magnetic moment which is randomly oriented as a result of thermal agitation.

The magnetic field creates a slight alignment of these moments and hence a low magnetisation in the same direction as the applied field.

Ferromagnetism Ferromagnetism is only possible when

atoms are arranged in a lattice and the atomic magnetic moments can interact to align parallel to each other.

Only Fe, Co and Ni are ferromagnetic at and above room temperature

Antiferromagnetism Antiferromagnetic materials are very similar to

ferromagnetic materials but the exchange interaction between neighboring atoms leads to the anti-parallel alignment of the atomic magnetic moments.

Ferrimagnetism

Ferrimagnetism is only observed in compounds, which have more complex crystal structures than pure elements

Classification of Magnetic Materials

Electromagnet An electromagnet is a wire that has been

coiled into one or more loops, known as a solenoid.

When electric current flows through the wire, a magnetic field is generated.

The more loops of wire, the greater the cross-section of each loop, and the greater the current passing through the wire, the stronger the field.

Uses for electromagnets include particle accelerators, electric motors, etc

The Orientation of Magnet The orientation of this effective magnet is

determined via the right hand rule.

Magnetic Phenomena

An electric current produces a magnetic field.

Some materials are easily magnetized when placed in a weak magnetic field. When the field is turned off, the material rapidly demagnetizes. These are called "Soft Magnetic Materials."

Magnetic Phenomena In some magnetically soft materials the electrical

resistance changes when the material is magnetized. The resistance goes back to its original value when the magnetizing field is turned off. This is called "Magneto-Resistance" or the MR Effect.

Certain other materials are magnetized with difficulty but once magnetized, they retain their magnetization when the field is turned off. These are called "Hard Magnetic Materials" or "Permanent Magnets."

HISTORY OF MAGNETIC RECORDERS

In 1888, Oberlin Smith originated the idea of using permanent magnetic impressions to record sounds.

In 1900, Vladeniar Poulsen demonstrated a Telegraphone. It was a device that recorded sounds onto a steel wire.

Although everyone thought it was a great idea, they didn't think it would succeed since you had to use an earphone to hear what was recorded.


Until 1935, all magnetic recording was on steel wire.

Then, at the 1935 German Annual Radio Exposition in Berlin, Fritz Pfleumer demonstrated his Magnetophone. It used a cellulose acetate tape coated with soft iron powder.

The Magnetophone and its "paper" tapes were used until 1947 when the 3M Company introduced the first plastic-based magnetic tape.


In 1956, IBM introduced the next major contribution to magnetic recording - the hard disk drive. The disk was a 24-inch solid metal platter and stored 4.4 megabytes of information.

Later, in 1963, IBM reduced the platter size and introduced a 14-inch hard disk drive.


In 1971, 3M Company introduced the first 1/4-inch magnetic tape cartridge and tape drive.

In that same year, IBM invented the 8-inch floppy disk and disk drive. It used a flexible 8-inch platter of the same material as magnetic tape.

In 1980, a little-known company named Seagate Technology invented the 5-1/4-inch floppy disk drive.

PREREQUISITES FOR MAGNETIC RECORDING

Input SignalRecording MediumMagnetic Head

Input Signal

An input signal can come from a microphone, a radio receiver, electrical device, or any other source that's capable of producing a recordable signal.

Some input signals can be recorded immediately, but some must be processed first.

This processing is needed when an input signal is weak, or is out of the Frequency response range of the recorder.

Recording Medium

A recording medium is any material that has the ability to become magnetized, in varying amounts, in small sections along its entire length.

Some examples of this are magnetic tape and magnetic disks

Magnetic Heads Magnetic heads are the transducers that

convert the electrical input signal into the magnetic that are stored on a recording medium.

Magnetic heads do 3 different things. Transfer signal onto the recording medium. Recover signal from the recording medium. Remove signal off the recording medium.

Writing Magnetic Data

Reading Magnetic Data

Integrating the Write/Read Heads

HDD Data Encode and Decode

Digital information is a stream of ones and zeros.

Hard disks store information in the form of magnetic pulses.

In order for the PC's data to be stored on the hard disk, therefore, it must be converted to magnetic information.

When it is read from the disk, it must be converted back to digital information.

HDD Data Encode and Decode

Magnetic information on the disk consists of a stream of very small magnetic fields.

Information is stored on the hard disk by encoding information into a series of magnetic fields.

This is done by placing the magnetic fields in one of two polarities: either N-S, or S-N

HDD Data Encode and Decode Although it is conceptually simple to

match "0 and 1" digital information to “N-S” and “S-N” magnetic fields.

The reality is much more complex: a 1-to-1 correspondence is not possible, and special techniques must be employed to ensure that the data is written and read correctly.

Technical Requirements

Fields vs. Reversals Synchronization Field Separation

Fields vs. Reversals

Read/write heads are designed not to measure the actual polarity of the magnetic fields, but rather flux reversals.

Flux reversals occur when the head moves from an area that has N-S polarity to S-N, or vice-versa.

Fields vs. Reversals

The reason the heads are designed based on flux reversals instead of absolute magnetic field, is that reversals are easier to measure.

The encoding of data must be done based on flux reversals, and not the contents of the individual fields.

Synchronization:

Another consideration in the encoding of data is the necessity of using some sort of method of indicating where one bit ends and another begins.

Even if we could use one polarity to represent a "one" and another to represent a "zero", what would happen if we needed to encode on the disk a stream of 1,000 consecutive zeros?

Field Separation

Although we can conceptually think of putting 1000 tiny N-S pole magnets in a row one after the other. They are additive.

Aligning 1000 small magnetic fields near each other would create one large magnetic field, 1000 times the size and strength of the individual components.

Data Encoding

We must encode using flux reversals, not absolute fields.

We must keep the number of consecutive fields of same polarity to a minimum.

To keep track of which bit is where, some sort of clock synchronization must be added to the encoding sequence.

Data Encoding

Media Limitation

Each linear inch of space on a track can only store so many flux reversals.

We need to use some flux reversals to provide clock synchronization, these are not available for data.

A prime goal of data encoding methods is therefore to decrease the number of flux reversals used for clocking relative to the number used for real data.

Media Limitation

Over time, better methods that used fewer flux reversals to encode the same amount of information.

Hardware technology strives to allow more bits to be stored in the same area by allowing more flux reversals per linear inch of track.

Encoding methods strive to allow more bits to be stored by allowing more bits to be encoded (on average) per flux reversal.

Data Encode/Decode Methods

Frequency Modulation (FM) Modified Frequency Modulation (MFM) Run Length Limited (RLL) Partial Response, Maximum Likelihood

(PRML) Extended PRML (EPRML)

Frequency Modulation (FM)

This is a simple scheme, where a one is recorded as two consecutive flux reversals, and a zero is recorded as a flux reversal followed by no flux reversal.

This can also be thought of as follows: a flux reversal is made at the start of each bit to represent the clock, and then an additional reversal is added in the middle of each bit for a one, while the additional reversal is omitted for a zero.

FM

Bit PatternEncoding

PatternFlux Reversals Per Bit

Bit PatternCommonality In

Random Bit Stream

0 RN 1 50%

1 RR 2 50%

Weighted Average 1.5 100%

FM The name "frequency modulation" comes from

the fact that the number of reversals is doubled for ones compared to that for zeros.

A byte of zeroes would be encoded as "RNRNRNRNRN…",

A byte of all ones would be "RRRRRRR……“ The ones have double the frequency of reversals

compared to the zeros; hence frequency modulation (meaning, changing frequency based on data value).

FM FM is very wasteful: Each bit requires two flux reversal

positions, with a flux reversal being added for clocking every bit.

Compared to more advanced encoding methods that try to reduce the number of clocking reversals, FM requires double (or more) the number of reversals for the same amount of data.

Modified Frequency Modulation MFM improves on FM by reducing the number of

flux reversals inserted just for the clock. Instead of inserting a clock reversal at the start of

every bit, one is inserted only between consecutive zeros.

When a 1 is involved there is already a reversal (in the middle of the bit) so additional clocking reversals are not needed.

When a zero is preceded by a 1, we similarly know there was recently a reversal and another is not needed. Only long strings of zeros have to be "broken up" by adding clocking reversals.

MFM

Bit PatternEncodingPattern

Flux Reversals Per Bit


Random Bit Stream

0 (preceded by 0) RN 1 25%

0 (preceded by 1) NN 0 25%

1 NR 1 50%


MFM Since the average number of reversals

per bit is half that of FM, the clock frequency of the encoding pattern can be doubled, allowing for approximately double the storage capacity of FM.

MFM MFM encoding was used on the earliest

hard disks, and also on floppy disks. Since the MFM method about doubles the

capacity of floppy disks compared to earlier FM ones, these disks were called "double density".

In fact, MFM is still the standard that is used for floppy disks today.

For hard disks it was replaced by the more efficient RLL methods.

Run Length Limited

An improvement on the MFM encoding is Run Length Limited or RLL.

This is a more sophisticated coding technique, or more correctly stated, "family" of techniques.

RLL is a family of techniques because there are two primary parameters that define how RLL works, and therefore, there are several different variations.

RLL

RLL takes MFM technique one step further.

It considers groups of several bits instead of encoding one bit at a time.

The idea is to mix clock and data flux reversals to allow for even denser packing of encoded data, to improve efficiency.

The two parameters that define RLL are the run length and the run limit (and hence the name).

RLL

The word "run" here refers to a sequence of spaces in the output data stream without flux reversals.

The run length is the minimum spacing between flux reversals, and the run limit is the maximum spacing between them.

As mentioned before, the amount of time between reversals cannot be too large or the read head can get out of sync and lose track of which bit is where.

RLL The particular variety of RLL used on a drive

is expressed as "RLL (X,Y)" or "X,Y RLL" X is the run length and Y is the run limit. The most commonly used types of RLL in

hard drives are "RLL (1,7)", and "RLL (2,7)" Consider the spacing of potential flux

reversals in the encoded magnetic stream. In the case of "2,7", this means that the smallest number of "spaces" between flux reversals is 2, and the largest number is 7.

RLL

Bit PatternEncodingPattern

Flux ReversalsPer Bit


Random Bit Stream

11 RNNN 1/2 25%

10 NRNN 1/2 25%

011 NNRNNN 1/3 12.5%

010 RNNRNN 2/3 12.5%

000 NNNRNN 1/3 12.5%

0010 NNRNNRNN 2/4 6.25%

0011 NNNNRNNN 1/4 6.25%


RLL

If we were writing the byte "10001111" (8Fh), this would be matched as "10-0011-11" and encoded as "NRNN-NNNNRNNN-RNNN".

Since every pattern above ends in "NN", the minimum distance between reversals is two.

The maximum distance would be achieved with consecutive "0011" patterns, resulting in "NNNNRNNN-NNNNRNNN" or seven non-reversals between reversals. Thus, RLL (2,7).

Peak Detection Standard read circuits work by detecting flux

reversals and interpreting them based on the encoding method.

The controller converts the signal to digital information by analyzing, synchronized to internal clock, and looking for small voltage spikes in the signal that represent flux reversals.

This traditional method of reading and interpreting hard disk data is called peak detection.

Peak Detection The circuitry scans the data read from the

disk looking for positive or negative "spikes" that represent flux reversals.

Peak Detection This method works fine as long as the

peaks are large enough to be picked out from the background noise of the signal.

As data density increases, the flux reversals are packed more tightly and the signal becomes much more difficult to analyze.

This can potentially cause bits to be misread from the disk.

Peak Detection

To take the next step up in density, the magnetic fields must be made weaker.

This reduces interference, but causes peak detection to be much more difficult.

At some point it becomes very hard for the circuitry to actually tell where the flux reversals are.

PRML To combat this problem a new method

was developed. This technology, called partial response,

maximum likelihood or PRML, changes entirely the way that the signal is read and decoded from the surface of the disk.

PRML

PRML employs sophisticated digital signal sampling, processing and detection algorithms to:

Manipulate the analog data stream coming from the disk (the "partial response" component)

Determine the most likely sequence of bits this represents ("maximum likelihood")

Extended PRML (EPRML)

An evolutionary improvement on the PRML is extended partial response, maximum likelihood, or EPRML.

This advance was the result of engineers tweaking the basic PRML design to improve its performance.

EPRML devices work in a similar way to PRML.

They just use better algorithms and signal-processing circuits.

EPRML

The chief benefit of using EPRML is that due to its higher performance, areal density can be increased without increasing the error rate. Claims regarding this increase range from around 20% to as much as 70%, compared to "regular" PRML.

EPRML has now been widely adopted in the hard disk industry and is replacing PRML on new drives.

Recording Head Technology

Recording Head Technologies

Ferrite Heads Metal-In-Gap (MIG) Heads Thin Film (TF) Heads (Anisotropic) Magnetoresistive (MR/AMR)

Heads Giant Magnetoresistive (GMR) Heads Colossal Magnetoresistive (CMR) Heads TMR Heads

Ferrite Heads The oldest head design is also the simplest

conceptually. When writing, the current in the coil creates

a polarized magnetic field in the gap between the poles of the core, which magnetizes the platter.

When the direction of the current is reversed, the opposite polarity magnetic field is created.

For reading, the process is reversed.

Ferrite Heads

Metal-In-Gap Heads

The improvement of ferrite head design was Metal-In-Gap heads.

They are essentially the same design, but add a special metallic alloy in the head.

This change greatly increases its magnetization capabilities, allowing MIG heads to be used with higher density media.

They are usually found in PC hard disks of about 50 MB to 100 MB.

Thin Film Head Thin Film (TF) heads--also called thin film

inductive (TFI)--are a totally different design from ferrite or MIG heads.

They are so named because of how they are manufactured.

TF heads are made using a photolithographic process similar to how processors are made.

Thin Film Head Thin film heads are capable of being used on

much higher-density drives and with much smaller floating heights.

They were used in many PC HDD in the late 1980s to mid 1990s, usually up to 1000 MB capacity range.

Thin Film Head Structure A thin film head structure consists of 20

material layers with patterns for each layer defined by photolithography and either additive processing (electroplating, liftoff masking) or subtractive processing (ion milling, wet etching, reactive ion etching, chemical mechanical processing).

Thin Film Head Structure

Critical Thin Film Head Features

Two critical features in the thin film head, the width of the read sensor (MRw) and the width of the write pole tip (P2w), determine areal density performance.

The lithography techniques for the MR sensor are comparable to gate requirements in integrated circuits. The lithography processing for the write pole tip can be compared with the interconnect processing strategy in the integrated circuit.

AMR Head The newest type of technology commonly

used in read/write heads is much more of a radical change to the way the read/write head works.

While conventional ferrite or thin film heads work on the basis of inducing a current in the wire of the read head in the presence of a magnetic field, magnetoresistive (MR) heads use a different principle entirely to read the disk.

AMR Head

An MR head employs a special conductive material that changes its resistance in the presence of a magnetic field.

As the head passes over the surface of the disk, this material changes resistance as the magnetic fields change corresponding to the stored patterns on the disk.

AMR Head The MR head is not generating a current directly

the way standard heads do, it is several times more sensitive to magnetic flux changes in the media.

This allows the use of weaker written signals, which lets the bits be spaced closer together without interfering with each other, improving capacity by a large amount.

AMR Head MR technology is used for reading the disk

only. For writing, a separate standard thin-film head is used.

This splitting of chores into one head for reading and another for writing has additional advantages.

Traditional heads that do both reading and writing are an exercise in tradeoffs, because many of the improvements that would make the head read more efficiently would make it write less efficiently, and vice-versa.

AMR Head

First introduced in 1991 by IBM but not used widely until several years later, MR heads were one of the key inventions that led to the creation of hard disks over 1 GB.

Despite the increased cost of MR heads, they have now totally replaced thin film heads.

AMR Head

Even MR heads however have a limit in terms of how much areal density they can handle.

The successor to MR is GMR heads, named for the giant magnetoresistive effect.

They are similar in basic concept to MR heads but are more advanced

GMR Head

First discovered in the late 1980s by two European researchers, Peter Gruenberg and Albert Fert, who were working independently.

Working with large magnetic fields and thin layers of various magnetic materials, they noticed very large resistance changes when these materials were subjected to magnetic fields.

GMR Head

IBM developed GMR into a commercial product by experimenting with thousands of different materials and methods.

A key advance was the discovery that the GMR effect would work on multilayers of materials deposited by sputtering.

By December 1997, IBM had introduced its first hard disk product using GMR heads.

GMR Head Technology

Evolution of R/W Head

Giant magnetoresistive effect

Giant Magnetoresistance (GMR) is a quantum mechanical effect observed in thin film structures composed of alternating ferromagnetic and nonmagnetic metal layers.

The effect manifests itself as a significant decrease in resistance to a lower level of resistance when sensing different magnetic field.

GMR Technology

The spin of the electrons of the nonmagnetic metal align parallel or antiparallel with an applied magnetic field in equal numbers, and therefore suffer less magnetic scattering when the magnetizations of the ferromagnetic layers are parallel.

Types of GMR

Multilayer GMR Granular GMR Spin valve GMR

Multilayer GMR

Two or more ferromagnetic layers are separated by a very thin (about 1 nm) non-ferromagnetic spacer (e.g. Fe/Cr/Fe).

The GMR effect was first observed in the multilayer configuration, with much early research into GMR focusing on multilayer stacks of 10 or more layers.

Granular GMR Granular GMR is an effect that occurs in

solid precipitates of a magnetic material in a non-magnetic matrix.

In practice, granular GMR is only observed in matrices of copper containing cobalt granules.

Granular GMR materials have not been able to produce the high GMR ratios found in the multilayer counterparts.

Spin valve GMR

Two ferromagnetic layers are separated by a thin (about 3 nm) non-ferromagnetic spacer.

If the coercive fields of the two ferromagnetic electrodes are different it is possible to switch them independently.

Therefore, parallel and anti-parallel alignment can be achieved, and normally the resistance is again higher in the anti-parallel case. This device is sometimes also called spin-valve.

Spin-valve GMR is the configuration that is most industrially useful, and is the configuration used in hard drives.

Spin valve GMR When the head passes

over a magnetic field of one polarity (say, "0"), the free layer electrons turn to be aligned with those of the pinned layer; this creates a lower resistance in the entire head structure.

Spin valve GMR

When the head passes over a magnetic field of the opposite polarity ("1"), the electrons in the free layer rotate so that they are not aligned with those of the pinned layer. This causes an increase in the resistance of the overall structure.

GMR head materials

Free Layer Spacer Pinned Layer Exchange Layer

Free Layer:

This is the sensing layer, made of a nickel-iron alloy, and is passed over the surface of the data bits to be read.

Spacer:

This layer is nonmagnetic, typically made from copper, and is placed between the free and pinned layers to separate them magnetically.

Pinned Layer:

This layer of cobalt material is held in a fixed magnetic orientation by virtue of its adjacency to the exchange layer.

Exchange Layer:

This layer is made of an "antiferromagnetic" material, typically constructed from iron and manganese, and fixes the pinned layer's magnetic orientation.

AMR VS GMR

AMR heads typically exhibit a resistance change of about 2%, for GMR heads this is anywhere from 5% to 8%.

GMR heads can detect much weaker and smaller signals, which is increasing areal density, capacity and performance.

GMR are much less subject to noise and interference because of their increased sensitivity, and they can be made smaller and lighter than MR heads

TMR Phenomena The magneto resistance in a tunnel-valve

originates from a change in tunneling probability dependent on the relative magnetic orientation of two ferromagnetic layers.

The response of a free ferromagnetic layer to the magnetic field of the storage media results in a change of electrical resistance in the tunnel-valve sensor.

Spin-Valve VS Tunnel Valve

TMR Read Head

Perpendicular Recording One of the key challenges facing the hard

drive industry is overcoming the constraints imposed by the superparamagnetic effect.

Which occurs when the microscopic magnetic grains on the disk become so tiny that ambient temperature can reverse their magnetic orientations.

The result is that the bit is erased and, thus, data is lost.

Perpendicular Recording

PMR Platter Structure

PMR Response

Today PMR HDD

2006 Seagate: the world's first 3.5 inch Cheetah 15K 300GB storage.

2006 Toshiba: 40GB MK4007GAL 1.8” HDD 2006 Fujitsu: 160GB MHW2160BH 2.5" HDD 2006 Seagate: Barracuda 7200.10, 750 GB

3.5” HDD. 2007 Hitachi announced the first 1 Terabyte

Hard Drive

PMR HDD

HDD HEAD Fabrications

Wafer fabrication processes

Wafer is the common word of raw material for ICs manufacturing. Usually thin, round and silicon crystal in diameter 150, 200 and 300 mm. The wafer fabrication is normally operated under vacuum and cleanroom.

1. Preparation of wafer media

2. Wafer processing

Preparation of wafer media

Wafer media is fabricated as substrate of next processes.

1. Crystal growth and wafer slicing

2. Thickness sorting

3. Lapping & etching

4. Thickness & flatness checking

5. Polishing

6. Final Testing

Wafer processing

Photolithography Additive processing

Thin film technology Subtractive processing

Wet etching Dry etching (Ion milling, Plasma etching,

Reactive ion etching) Modifying (dopant)

Diffusion Ion implantation

Basic of head slider fabrication

Slider fabrication is the process of parting wafer containing thousands of recording heads into a form factor called slider.

Each slider embodying one recording head. The flying height of less that 10 nm has

mandated the use of the most advanced micromachining and vacuum technologies to deliver the extreme mechanical sophistications required in the sliders.

Fly Height?

Basic of head slider fabrication Thin and polish wafer by lapping Bonded the entire wafer to a platform Wafer slicing into row of slider by multi-

blade The rows are processed in various

ways, including lapping and ion milling to form air bearing surface (ABS)

Dividing to each slide

HGA - HSA

Basic of media fabrication

Glass substrate

highly planar low defect Smoothness Suit modulus which yields stable

mechanical properties in the drive

Glass substrate fabrication

Design of Glass Composition Glass Melting and Molding Machining Brittle Materials Precision Cleaning

Glass Substrates Manufacturing

Magnetic Media

Under layer – Cr Magnetic layer – CoPtCrB Antiferromagnetic layer – Ru Can be fabricated by decomposition

techniques such as sputtering The Ruthenium layer is about 3 atom-thick

layer

RECORDING HEAD TECHNOLOGY BASIC School of Mechanical Engineering Institute of Engineering Suranaree...

Documents

Transcript of RECORDING HEAD TECHNOLOGY BASIC School of Mechanical Engineering Institute of Engineering Suranaree...