Ferromagnetism in Transition metal doped ZnO thin films by Pulsed Laser Depostion

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Ferromagnetism in Transition metal doped ZnO thin
films by Pulsed Laser Depostion
By Venkatesan Dhanasekaran Yanuo Shi Smart
Electronics Materials Project
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Content

• Objective of the project
• Origin of Magnetism
• Zinc Oxide Introduction and Applicantions
• Dilute Magnetic Semiconductors
• Mechanisms of DMS
• Pulsed Laser Deposition Thin films
• Literatures on Co, Ni, Mn doped ZnO thin films
• Conclusion

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Objective and Goals

• Understanding the principles behind transitional
  metal ions doped ZnO thin films called as Dilute
  Magnetic Semiconductors
• Intensive literature survey to attain
  experimental results of the principles.

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Origin of Magnetism
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Types of Magnetism
Paramagnetism
Ferromagnetism
Fe, Ni, Co, Mn, Cr Rare earths
Mg,O, N, F
Diamagnetism
Football, ice cream, Shoes, plastic covers
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FERROMAGNETIC MATERIALS d block elements
Electronic Arrangement Electronic Arrangement Electronic Arrangement Electronic Arrangement Electronic Arrangement Electronic Arrangement Electronic Arrangement Electronic Arrangement
Element Z 3d 3d 3d 3d 3d 4s
Sc 21 Ar ? ??
Ti 22 Ar ? ? ??
V 23 Ar ? ? ? ??
Cr 24 Ar ? ? ? ? ? ?
Mn 25 Ar ? ? ? ? ? ??
Fe 26 Ar ?? ? ? ? ? ??
Co 27 Ar ?? ?? ? ? ? ??
Band structure for Co in 4s and 3d states at
absolute zero
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• ZnO is a II-VI semiconductor because zinc and
  oxygen belong to the 2nd and 6th group.
• Crystal Structure - Hexagonal Wurtzite.
• Relatively large direct band gap of 3.37 eV
  at room
  temperature.
• It is n-type character, even in the absence
  of intentional doping.
• High electron mobility, wide band gap, strong
  room-temperature luminescence.

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Application of ZnO

• Light emitting diodes (LED) and Laser diodes (LD)
• Wide band gap
• Drawback is p-type ZnO

• Piezoelectric property
• lighter, speaker, varistors, buzzer,
• - self powered nano generators

ZnO
Dilute Magnetic Semiconductors (DMS) - Room
temperature Ferromagnetism

• Solar cells
• Transparent conducting oxide
• - large band and small resistivity

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Dilute Magnetic Semiconductors (DMS)
Semi-conductor
M Field
M Field
M Field
M Field

• Diluted Magnetic Semiconductor (DMS)
• Traditional semiconductors doped with
  transition metals
• Why Dilute? small doping concentration (a
  few )
• Why Magnetic? Display
  ferromagnetisation
• Why Semiconductor? While preserving the
  semiconducting properties

Dopants
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Principle of DMS
Defect based Intrinsic defects in the
semiconducting system. ZnO - Zinc and oxygen
vacancies. InDMS, Theoritical ? Experimental Not
al dopant contribute Large dopant -gt
anti-ferromagnetism
Vs
Magnetism due to external dopants in a
semiconducting system
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Mechanism of Magnetic Interaction in Dilute
Magnetic Semiconductor Metal Oxides

• Consider a model of band structure, in which two
  electronics subsystems were distinguished
• The Hamiltonian interaction can be written as
• Hspin -I.s.S
• s - carrier spin (host ZnO),
• S - transition metal spin (d-block dopant)
• I - strength of the interaction between the
  carrier spin and the transition metal spin
• Other Mechanism Double exchange, Super
  exchange, Zener/RKKY models, Donor impurity band
  exchange

electrons causing magnetic moments in dopants
delocalized band of (native) electrons of host -
ZnO
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Pulsed Laser Deposition (PLD)

• Parameters
• Pressure
• Substrate
• Tsub
• Laser energy
• Distance (T-S)
• Enviroment
• Deposition time

Vacuum chamber
Fig Working model of Pulsed Laser Deposition
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Wide usage of PLD

• Ultra High Vacuum and Different Gas Atmospheres
• Small Target Size
• Stoichiometry Transfer
• Pulsed Nature of PLD
• Energetic Particles
• Tunable Particle Energy

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Survey on transition metal ion doped ZnO thin
films by PLD
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Preparation of CoZnO at different substrate
temperature

• Experiment
• Single Al2O3 crystal substrate (Cleaned and
  Di-Ionized)
• Target (10 CoO powder90ZnO powder sintered at
  1000?C for 3h)
• The deposition pressure of the chamber - 1 10-4
  Torr oxygen partial pressure
• Different Substrate temperature gt 25oC, 100 oC,
  600 oC

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Results and Discussions
Ms42 emu/cc
Ms22 emu/cc
Crystallinity
230 Oe
No Co Segregation
130 Oe
Fig. . The XRD patterns of Co-dopedZnO thin
films, with different substrate temperatures
during deposition. Insert - The full width half
maximum of the zincite (0 0 2) peak rocking curve
is only 0.25?
Fig. 2. MH curve of the films deposited at 100
?C and 600 ?C as indicated in the figure. Inset
shows the enlarge graph for the coercivity
information.
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Different Concentration of Co in ZnO
Figure XRD pattern of CoZnO thin films, at
varying Co content.
Figure XRD scans for a series of ZnO Co films
grown in vacuum at 400 C.
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Different Concentration of Ni in ZnO
Sec phase
Lattice constant
Figure XRD pattern of NiZnO thin films, at
varying Ni content
Figure Relation between lattice parameter and
Ni concentration.
Figure MH curve of the NiZnO films at varying
Ni concentration
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Different Concentration of Mn in ZnO
Table 1 Summary of magnetic properties for
MnZnO thin film at low temperature and room
temperature.
Figure MH curve of the MnZnO films at varying
Mn concentration
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Conclusion

• Origin of magnetism
• Intro to ZnO
• DMS and principles
• Pulsed laser deposition
• Effect of different substrate temperature on thin
  films
• Effect of different types of dopants in thin
  films
• Conclusion
• References

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Acknowledgement
Prof. Alexander Grishin Condensed Matter
Physics, KTH, Sweden
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Thank you for your attention !
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References

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