Published on: Mar 5, 2016
Transcripts - Nano materials
Iron single crystal photomicrographs
magnetic domains change shape as a
magnetic field (H) is applied.
domains favorably oriented with the field
grow at the expense of the unfavorably
Forces can be represented by imaginary lines grouped as fields
Magnetic forces appear when moving charges
Magnetic field lines of force around a current loop and a bar magnet.
The magnetic moment represented by a vector
Magnetic Field Vectors
magnetic field strength (H) & magnetic flux density (B)
Magnetic flux density
H = B
B = H 0 0
= + 0 0B H M
M = H m
= -1 m r
Magnetic field strengthH =
Origins of Magnetic Moments:
Responds to quantum mechanics laws
Two main contributions: (a) an orbiting electron and (b) electron spin.
Bohr magneton (B)
Most fundamental magnetic moment
B = ±9.27x10-24 A-m2
The spin is an
property of the
electron and it
is not due to its
18.3 Diamagnetism and Paramagnetism
in the presence of a field, dipoles
are induced and aligned opposite
to the field direction.
The flux density B versus the magnetic field
strength H for diamagnetic and paramagnetic
B = 0H + 0M = 0H + 0mH
= 0(1 + m)
mutual alignment of atomic
even in the absence of an external
coupling forces align the magnetic
B H M
Domains with mutual spin alignment
B grows up to a saturation magnetization Ms with a saturation flux
Bs = Matom × Natoms (average moment per atom times density of atoms)
Matom = 2.22B, 1.72B, 0.60B for Fe, Co, Ni, respectively
discovered in layered
with a transition T much
higher than expected.
Little was known about
Antiferromagnetism & Ferrimagnetism
Antiparallel alignment of spin
magnetic moments for
At low T
Above the Neel temperature they
Parent materials, La2CuO4, and YBa2Cu3O6,
demonstrated that the CuO2 planes exhibit
This work initiated a continuing exploration
of magnetic excitations in copper-oxide
superconductors, crucial to the mechanism
of high-temperature superconductivity.
spin magnetic moment
configuration for Fe2+ and Fe3+ ions
in Fe3O4. Above the Curie
18.6 The Influence of Temperature on magnetic Behavior
TC: Curie temperature (ferromagnetic, ferrimagnetic)
TN: Neel temperature (antiferromagnetic)
material become paramagnetic
18.7 Domains and Hysteresis
Domains in a ferromagnetic or ferrimagnetic
material; arrows represent atomic magnetic
Within each domain, all dipoles are aligned,
whereas the direction of alignment varies from
one domain to another.
Gradual change in magnetic dipole
orientation across a domain wall.
B versus H
during several stages of
Saturation flux density, Bs
initial permeability i
Magnetic flux density
versus magnetic field
subjected to forward and
reverse saturations (S & S’).
hysteresis loop (red)
initial magnetization (blue)
coercive force, Hc
Comparison magnetic versus nonmagnetic
dependence of the electrical resistivity
for normally conducting and
superconducting materials in the
vicinity of 0 K.
current density, and magnetic
field boundary separating
superconducting and normal
conducting states (schematic).
the Meissner effect.
While in the superconducting state, a body of
material (circle) excludes a magnetic field
(arrows) from its interior.
The magnetic field penetrates the same
body of material once it becomes
• A magnetic field can be produced by:
--putting a current through a coil.
• Magnetic induction:
--occurs when a material is subjected to a magnetic field.
--is a change in magnetic moment from electrons.
• Types of material response to a field are:
--ferri- or ferro-magnetic (large magnetic induction)
--paramagnetic (poor magnetic induction)
--diamagnetic (opposing magnetic moment)
• Hard magnets: large coercivity.
• Soft magnets: small coercivity.
• Magnetic storage media:
--particulate g-Fe2O3 in polymeric film (tape or floppy)
--thin film CoPtCr or CoCrTa on glass disk (hard drive)