1. TATVA INSTITUTES OF TECHNOLOGICAL STUDIES,MODASA
PRESENTATION ON
Introduction to Optoelectronics Optical storage
ENROLL NO _

2. Storages Old storage: stones, paper, films, photographs, record
Advanced storage
Audio/Video use
Analog: audio cassette, video tape
Digital: CD, MD, Digital video tape, DVD, HD
Computer use
Magnetic: MT, FD, HD
Optical: CD-ROM, CD-R, CD-RW, MO, DVD-ROM, DVD-R, DVD-RW
Semiconductor: Flash memory (USB memory)

3. Old storages Woods, Bamboo Stone: example Rosetta Stone
Paper: books, notebooks, etc.
Films: movies, photographs

4. Magnetic Tape (MT)
Tape recorder

5. Magnetic recording History Magnetic tape and magnetic disk
Recording media and recording head
GMR head for high density
Magneto-optical recording
Hybrid magnetic recording
Solid state nonvolatile magnetic memory (MRAM)

6. History of magnetic recording
1898 V. Poulsen (Denmark) invented wire recorder; Information storage technology by control of magnetic state.
1900 The magnetic recorder was exhibited at the Paris EXPO and was praised as “the most interesting invention of recent years”.
Invention of vacuum tube amplifier by L. De Forest (USA) in1921, together with development of the ring-type magnetic head and the fine magnetic powder applied tape bring about practical magnetic recorder.

7. Recording process Recording current time moving direction
of recording media
Recorded wavelength
K. Sato ed., Applied Materials Science
(Ohm publishing) Fig. 5.18

8. Recording process
Signal current is applied to a coil in the magnetic head which is placed close to the recording medium to generate the magnetic flux, the intensity and direction of which is proportional to the signal.
The medium is magnetized by the magnetic flux from the head, leading to formation of magnetic domain corresponding to the intensity and polarity of the signal.
Recorded wavelength （the length of recorded domain corresponding to one period of the signal) is calculated by =v/f where v is the relative velocity between head and medium, and f the signal frequency)

9. Read out of recorded signal（1） Inductive head
Electromagnetic induction Electric voltage proportional to the derivative of the magnetic flux is generated
Output has the differential form of the recorded signal
The readout voltage is proportional to the product of the recorded wavelength and relative velocity between the head and the medium.
Spacing loss
Principle of read-out
induction
Running direction
K. Sato ed., Applied Materials Science
(Ohm publishing) Fig. 5.19, 5.20

10. Read out of recorded signal（2） MR (magneto-resistance) head
Change of the electric resistance of the head by the magnetic flux from the medium is utilized.
AMR (anisotropic magneto-resistance) was utilized in the early stage and was replaced to GMR (giant magneto-resistance).
N S
leakage flux
MR head

11. Magnetization curve and GMRF1 F2 F1 F2 F1 F2 H M R
HC1
HC2 F1 F2 F1 F2
If F1 and F2 have different Hc then high resistivity state is realized for H between Hc1 and Hc2
Resistance is high
for anti-parllel configuration

12. What is GMR? Ferromag(F１)/Nonmag(N)/Ferromag(F2) multilayer
Small resistance for parallel spin direction of F1 and F2, while high resistance for antiparallel direction.
Pinned layer
Free layer

13. Spin valve
NiFe(free)/Cu/NiFe(pinned)/AF(FeMn) uncoupled sandwich structure
Free layer
Nonmagnetoc
layer
Exchange bias
Pinned layer
Antiferromagnetic
(例 FeMn)
Synthetic antiferro

14. Head clearance

15. Thank You