123seminarsonly.com email us for more reports [email protected].

123seminarsonly.com email us for more reports [email protected]

Known technically as "antiferromagnetically-coupled (AFC) media," the new multilayer coating is expected to permit hard disk drives to store 100 billion bits (gigabits) of data per square inch of disk area by 2003

Current hard drives can store 20 gigabits of data per square inch.


Read-Rite's recording heads are the miniaturized hearts of disk drives and other magnetic storage devices.


A B C D

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.

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. Giant Magneto-Resistance, or the GMR Effect, is much larger than the MR Effect and is found in specific thin film materials systems.

Certain other materials are magnetized with difficulty (i.e., they require a strong magnetic field), but once magnetized, they retain their magnetization when the field is turned off. These are called Hard Magnetic Materials or Permanent Magnets.

Magnetic Phenomena Magnetic Phenomena


Writing HeadsHeads used for writing bits of information onto a spinning magnetic disk depend on phenomena A and B to produce and control strong magnetic fields.

Reading HeadsReading heads depend on phenomena A, B, and C, and are sensitive to the residual magnetic fields of magnetized storage media (D).

Storage MediaMagnetic storage media are permanently magnetized in a direction (North or South) determined by the writing field. Storage media exploit phenomenon D.


Computers store data on a rotating disk in the form of binary digits

These bits are converted into an electric current waveform that is delivered by wires to the writing head coil.

a one bit corresponds to a change in current polarity, while a zero bit corresponds to no change in polarity of the writing current.


recording heads read magnetic data with magnetically sensitive resistors called Spin Valves

GMR/Spin Valve heads are placed in close proximity to a rotating magnetized storage disk.


When a current is passed through the GMR element, changes in resistance and hence voltage voltage changes occur.

combined signal and noise from a GMR reader are sent via wires to the disk-drive electronics for decoding the time sequence of pulses (and spaces between pulses) into binary ones and zeroes.


As hard drives become capable of storing more information and accessing it at faster speeds, their data becomes more susceptible to corruption. This data-density barrier is known as the superparamagnetic effect (or SPE).


Hard drive resembles a small record player that's capable of stacking its disks, or platters, to hold up to eight of them at a time.

Each platter is covered with a magnetic film that is ingrained with tiny particles called bits.


When a read-write head passes over the bits, it either magnetically aligns the particles to record information or it reads them in order to access previously-stored data.


SPE destabilizes the 0 or 1-orientation of magnetic bits, resulting in corruption of stored data. When the energy in the bits' atoms approaches the thermal energy around them, the bits start randomly switching between 0's and 1's.

SPE makes bits flip out. The superparamagnetic effect originates

from the shrinking volume of magnetic grains that compose the hard-disk media, in which data bits are stored as alternating magnetic orientations.


Signal/Noise ~ N0.5

where N is the number of media grains per bit.

At smaller grain volumes, grains can randomly reverse thair magnetisation direction, resulting in an exponential decay whose rate strongly depends on temperature.


data density of about 10 gigabits/inch2 with an average grain diameter of about 13 nanometers.

a data density of 25 gigabit/inch2 with an average grain diameter of about 8.5 nanometers.


is expected to extend the lifetime of longitudinal magnetic recording technology.

Afc media differ from the conventional media by their structure and functionality. Conventional recording media have one or more magnetic layers, which may be coupled ferromagnetically to each other.


there are at least two magnetic layers, but the magnetic layers are coupled antiferromagnetically.

In comparison to conventional media, AFC media exhibit similar or better recording performance. But, at the same time, AFC media show much improved thermal stability, which makes them attractive.


based on adding extra energy in the form of antiferromagnetic coupling to stabilize the bits.

AFC media is a multi-layer structure in which two magnetic layers are separated by an extraordinarily thin -- just three atoms thick -- layer of the nonmagnetic metal, ruthenium.


This precise thickness of the ruthenium causes the magnetization in each of the magnetic layers to be coupled in opposite directions -- anti-parallel -- which constitutes antiferromagnetic coupling.


Mrteff = Mrttop – Mrtbottom

This property of the AFC media permits its overall Mrt to be reduced -- and its data density increased -- independently of its overall physical thickness.


growth rate in the areal density of hard disk drives has been around 60-100% per year.

introduction of GMR heads made reduction in grain size and thickness of media

This thermal instability is one of the major obstacles towards achieving areal densities beyond 40Gb/in2.


thermal stability of the media can be improved by choosing media materials with a higher Ku.

some additional energy to KuVwithout increasing the permanent magnetization. This condition is satisfied if we use an antiferromagnetic underlayer or some kind of antiferromagnetic coupling in the magnetic layers.123seminarsonly.com email us for more reports

[email protected]

Etotal = EAnis + EZeeman + EExchange + EMagnetostatic + EAnti + EThermal


AFC media is the first dramatic change in disk drive design made to avoid the high-density data decay due to the superparamagnetic effect.

thermal stability noise reduction in AFC Media by

decreasing the anisotropy constant


it can be made using existing production equipment at little or no additional cost, and that its writing and readback characteristics are similar to conventional longitudinal media.


Desktop drives -- 400 gigabytes (GB) or the information in 400,000 books

Notebook drives -- 200 GB, equivalent to 42 DVDs or more than 300 CDs

IBM's one-inch Microdrive -- 6 GB or 13 hours of MPEG-4 compressed digital video (about eight complete movies) for handheld devices.


we can expect to see 400GB desktop drives and 200GB notebook drives within another year or so, according to IBM scientists. Fujitsu is using similar technology. Fujitsu's SF Media uses a recording medium made up of two magnetic layers separated by a thin layer of ruthenium.


In summary, IBM has developed and is now mass-producing a promising new disk-drive media technology based on AFC multilayers that can enable significant areal density increases while maintaining the thermal stability of recorded data. This advancement will permit magnetic hard-disk drive technology to extend far beyond the previously predicted "limits" imposed by the superparamagnetic effect.


www.computerworld.com www.thefreelibrary.com www-03.ibm.com www.sciencedaily.com www.extremetech.com


123seminarsonly.com email us for more reports [email protected].

Documents

Transcript of 123seminarsonly.com email us for more reports [email protected].