Outline

1
Outline

• How is ferromagnetism manifested?
• What are the types of magnetism?
• What is Fe3O4 spinel?
• What is nanoscience?
• How do we make ferrofluids?

2
We will have a Monday class next week

• Turn in extra credit
• Writing exercises will be returned
• Possible chance for regaining lost points
• SRTI evaluations

3
Magnetic field
attraction
S
S
N
N
repulsion
S
S
N
N
The field of a force a property of the space in
which the force acts
http//www.trincoll.edu/cgeiss/GEOS_312/GEOS_312.
htm
4
Interaction with magnetic field
B
aligning torque
m pd
m AIn
t m B sin?
p
d
?
?
-p
http//www.trincoll.edu/cgeiss/GEOS_312/GEOS_312.
htm
5
Magnetic field (force lines)
F
S
N
Magnetic field is not a central field (no free
magnetic charges)
http//www.trincoll.edu/cgeiss/GEOS_312/GEOS_312.
htm
6
Behavior of magnetic materials
Magnetization (cm or mB or M)
Ferromagnet, Ferrimagnet
Paramagnet
Antiferromagnet
Temperature
TNeel
TCurie
7
Types of bulk magnetism
Ferromagnetism
Antiferromagnetism
Ferrimagnetism
Paramagnetism
H
Large M (1-5 mB / atom)
Small M (10-3 mB / atom)
Small M (10-3 mB / atom)
Large M (1-5 mB / atom)
8
Development of permanent (hard) magnets
Hard magnets
Soft magnets
M
M
http//www.tf.uni-kiel.de/matwis/amat/elmat_en/kap
_4/backbone/r4_3_6.html
9
What is nanoscience?
10

• ZnO nanowire UV lasers of about 100nm diameter
  and 10mm length synthesized at Berkeley. (Yang
  et al, Science, 292, p. 1897, 2001).

Contacts on a 60nm bismuth wire to study motion
of single defects (kmf.pa.msu.edu/Research/resrch
04.asp )
ZnO nanowire UV lasers of about 100 nm diameter
and 10 mm length synthesized at Berkeley. (Yang
et al, Science, 292, p. 1897, 2001)
11
Radius rules

• A sphere of this size (relative to the lattice of
  size of its neighbors) is just able to touch all
  off its neighbors for the void geometries below.

CN Relative radius Void geometry Polyhedron name
2 lt15.5 Linear Line
3 15.5 Triangular Triangle
4 25.5 Tetrahedral Tetrahedron
6 41.4 Octahedral Octahedron
8 73.2 Cubic (BCC) Cube
12 100 Cuboctahedral (HCP, CCP) Cuboctahedron

• Similar considerations govern the formation of
  more complex structural arrangements

12
Arrangements of nanoparticles mimics
arrangements of atoms
13
Some arrangements are very complex
14
Electronic and magnetic materials can be combined
into sophisticated devices
15
Magnetite
Fe3O4

• Magnetite vs. lodestone
• General spinel formula AB2O4
• A 2 metal, B 3 metal
• 1/2 of octahedral holes, 1/8 of tetrahedral holes
  filled on an approximate FCC oxygen lattice
• Fe3O4 1 Fe2 2 Fe3
• Inverse spinel B(AB)O4
• Ferrimagnetic ordering at 850K

• Synthesis 2 FeCl3 FeCl2 8 NH3 4H2O --gt
  Fe3O4 8 NH4Cl

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Magnetite (Fe3O4)
Unit cell A-sites (8 Fe3) B-sites (8 Fe3 and 8
Fe2)
Normal Spinel (ZnFe2O4)
Inverse Spinel (Fe3O4)
A
B
A
B
gt
Ferrimagnetism
Zn2
Fe3
Fe3
Fe3
Fe3
Fe2
5µB
5µB
4µB
17
Development of permanent (hard) magnets
M
Nd2Fe14B
Magnetic energy (Gauss / m3)
M
Steel
http//www.tf.uni-kiel.de/matwis/amat/elmat_en/kap
_4/backbone/r4_3_6.html
18
Ferrofluids of 10nm ferrite particles
19
Ferrofluids
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Types of bulk magnetism
Ferromagnetism
Antiferromagnetism
Ferrimagnetism
Paramagnetism
H
Large M (1-5 mB / atom)
Small M (10-3 mB / atom)
Small M (10-3 mB / atom)
Large M (1-5 mB / atom)
23
Canted Antiferromagnetism
Ferromagnetism
Antiferromagnetism
Ferrimagnetism
H
Canted Antiferromagnetism
Ferromagnetism
Antiferromagnetism
Ferrimagnetism
H
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Ferromagnetism
Antiferromagnetism
Ferrimagnetism
Paramagnetism
H
Ferromagnetism
Antiferromagnetism
Ferrimagnetism
Paramagnetism
H
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Types of magnetism
Ferromagnetism
Antiferromagnetism
Ferrimagnetism
Paramagnetism
H
Large M (1-5 mB / atom)
Small M (10-3 mB / atom)
Small M (10-3 mB / atom)
Large M (1-5 mB / atom)
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Ferrofluid topics

• Magnetic dipoles, not monopoles like charges
• Field gradient - emphasized by magnetic field
  lines
• A test dipole will aligns itself parallel to
  magnetic field lines

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Development of permanent (hard) magnets
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