hard magnetic material and magnetic storage

Hard magnetic materials

1. Hard magnetic materials are used in permanent magnetic which have high resistance to demagnetization.
2. Hard magnetic materials have high value of retentivity, coercivity, saturation flux density as well as low initial permeability and high hysteresis energy loss.
3. Conventional hard magnetic materials are

• Magnet steels
• Cunife (Cu-Ni-fe) alloys, alnico (Al- Ni- Co) as well as hexagonal ferrites (BaO-6\(Fe_2O_3)\)

4. High energy hard magnetic materials: Permanent magnetic materials having energy product in access of about 80 KJ/\(m^3\) are considered to be high energy type. These are commercially used hard magnetic materials. They are:-

• Samarium – cobalt magnets and Neodymium – iron- boron magnets

5. Familiar motor screwdriver and cordless drills.
6. In auto mobiles : window, wiper, washer, fan motors.
7. In audio recorder, video recorder.
8. Clocks, speaker, light weight earphones memory device such as computer.

Magnetic storage:

1. Magnetic materials are important in the area of information storage such as computers ipods, mp3 players, high definition cam coders, credit cards.
2. In computers, semiconductors elements are primary memory storage device where as magnetic hard disk are secondary memory device because they are capable of storing large quantity of information at lower cost.
3. Recording and reproduction of audio video signal in television industry completely rely on magnetic tapes for the storage.
4. In computer bytes, sound or visual image in the form of electrical signals are recorded magnetically on a very small segment of magnetic storage medium.

• A tape
• A disk

5. Two types of basic mechanism are
6. Transference or writing
7. Retrieval of information (reading) the tape or a disk. This reading is done by the means of recording system that consist of read and write heads.
8. For hard drives the head system is supported above an enclose proximity to magnetic medium by self generating air bearing as medium passes beneath at relatively high rotational speed i.e. tapes make physical contact with head during read write operation.

The two types of magnetic media are

1.HDD ( hard disk drive)

2.Magnetic tapes

HDD

1. Hard disk magnetic storage consists of rigid circular disk having diameter in the range between 65 mm to 95 mm.
2. During read and write process disk rotate at relatively high velocities 5400 to 7200 revolution per minute. Magnetic bits point up or down perpendicular plane of disk surface as shown in figure.
3. Data are introduced written in to storage medium using inductive write head.
4. A time varying write magnetic flux is generated at the tip of magnetic pole. A ferromagnetic or ferromagnetic core material is wounded by electric current.
5. The magnetic flux penetrates the magnetic storage layer into magnetically soft under layer then reenters the head assembly through a writer pole as shown in figure.
6. A very intense magnetic field is concentrated in the storage layer beneath the tip of magnetic pole. At this point data are written as a very small region of storage layer that become magnetized. Upon removal of field the disk continue their rotation magnetization remains that are signal data that is store.
7. The digital data storage is in the form of small magnetization pattern. The 0 and 1 corresponds to absence or present of magnetic reversal direction between adjacent regions.
8. A magnetic resistance read head is used to obtained data from storage medium. During read back magnetic fields from the returned magnetic pattern are senses by this head. This field produce change in electrical resistance the resulting signals are then processed as to received original data.

Magnetic tapes:

1. The magnetic tape storage is less expensive than HDD. In this case tapes are wound into reels and enclosed with in cartridges for protection and easy handling.
2. During operation, a tape device using precision motors winds the tapes from one reel to another. A read write head system in order store data. The principals for the storage
3. The storage media are particle of magnetic materials that have dimension of tense of nanometer. Ferromagnetic metal particles that a circular and hexagonal, tabular ferrimagnetic barium particle.
4. This particle are magnetized to form of magnetic layer that is approximately 50 nm.

References:

Callister, W.D and D.G Rethwisch. Material Science and Engineering. 2nd. New Delhi: Wiley India, 2014.

Lindsay, S.M. Introduction of Nanoscience . New York : Oxford University Press, 2010.

Patton, W.J. Materials in industry . New Delhi : Prentice hall of India, 1975.

Poole, C.P. and F.J. Owens. Introduction To Nanotechnology. New Delhi: Wiley India , 2006.

Raghavan, V. Material Science and Engineering. 4th . New Delhi: Pretence-Hall of India, 2003.

Tiley, R.J.D. Understanding solids: The science of Materials. Engalnd : John wiley & Sons , 2004