Post on 21-Dec-2015
transcript
Outline
• How is ferromagnetism manifested?
• What are the types of magnetism?
• What is Fe3O4 – spinel?
• What is nanoscience?
• How do we make ferrofluids?
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
S S
SSN
N N
N
The field of a force – a property of the space in which the force acts
Magnetic field
attraction
repulsion
http://www.trincoll.edu/~cgeiss/GEOS_312/GEOS_312.htm
θ
Interaction with magnetic field
m = AInm = pd
+p
-p
dτ = m B sinθ
B
θ
aligning torque:
http://www.trincoll.edu/~cgeiss/GEOS_312/GEOS_312.htm
Magnetic field (force lines)
Magnetic field is not a central field (no free magnetic charges)
SN
F
http://www.trincoll.edu/~cgeiss/GEOS_312/GEOS_312.htm
Behavior of magnetic materials
TNeel TCurie
Ferromagnet, Ferrimagnet
Antiferromagnet
Paramagnet
Magnetization
(m or B or M)
Temperature
Types of bulk magnetism
Ferromagnetism Antiferromagnetism Ferrimagnetism
Large M
(1-5 B / atom)
Small M
(10-3 B / atom)
Large M
(1-5 B / atom)
H
Small M
(10-3 B / atom)
Paramagnetism
Development of permanent (hard) magnets
M M
http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_4/backbone/r4_3_6.html
Hard magnets Soft magnets
What is nanoscience?
Contacts on a 60nm bismuth wire to study motion of single defects (kmf.pa.msu.edu/Research/resrch04.asp )
ZnO nanowire UV lasers of about 100nm diameter and 10mm length synthesized at Berkeley. (Yang et al, Science, 292, p. 1897, 2001).
ZnO nanowire UV lasers of about 100 nm diameter and 10 m length synthesized at Berkeley.(Yang et al, Science, 292, p. 1897, 2001)
Radius rules
CNRelative
radiusVoid geometry Polyhedron name
2 <15.5% 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
• 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.
• Similar considerations govern the formation of more complex structural arrangements
Arrangements of nanoparticles mimics arrangements of atoms
Some arrangements are very complex
Electronic and magnetic materials can be combined into sophisticated devices
Magnetite
• 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
Fe3O4
• Synthesis: 2 FeCl3 + FeCl2 + 8 NH3 + 4H2O --> Fe3O4 + 8 NH4Cl
Magnetite (Fe3O4)
Unit cell:
A-sites (8 Fe3+)
B-sites (8 Fe3+ and 8 Fe2+)
Ferrimagnetism
Normal Spinel (ZnFe2O4) Inverse Spinel (Fe3O4)
A B
Zn2+ Fe3+ Fe3+
A B
Fe3+ Fe3+ Fe2+=>
5µB 5µB 4µB
Development of permanent (hard) magnetsM
agne
tic
ener
gy (
Gau
ss /
m3 )
Steel
Mag
neti
c en
ergy
(G
auss
/ m
3 )
Steel
Nd2Fe14B
M
M
http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_4/backbone/r4_3_6.html
Ferrofluids of ~10nm ferrite particles
Ferrofluids
Types of bulk magnetism
Ferromagnetism Antiferromagnetism Ferrimagnetism
Large M
(1-5 B / atom)
Small M
(10-3 B / atom)
Large M
(1-5 B / atom)
H
Small M
(10-3 B / atom)
Paramagnetism
Ferromagnetism Antiferromagnetism Ferrimagnetism
H
Canted Antiferromagnetism
Ferromagnetism Antiferromagnetism Ferrimagnetism
H
Canted Antiferromagnetism
Ferromagnetism Antiferromagnetism
H
Ferromagnetism Antiferromagnetism
H
Ferrimagnetism
Ferrimagnetism
Paramagnetism
Paramagnetism
Ferromagnetism Antiferromagnetism Ferrimagnetism
Large M
(1-5 B / atom)
Small M
(10-3 B / atom)
Large M
(1-5 B / atom)
H
Small M
(10-3 B / atom)
Paramagnetism
Types of magnetism
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
Development of permanent (hard) magnets
MM