Download Types of Magnetism and Magnetic Domains

Types of Magnetism and Magnetic Domains
Magnets or objects with a Magnetic Moment
• A magnet is an object or material that attracts certain
metals, such as iron, nickel and cobalt.
• It can also attract or repel another magnet.
• All magnets have North-seeking (N) and South-seeking
(S) poles.
• When magnets are placed near each other, opposite
poles attract and like poles repel each other.
Types of magnets (The Boad View)
Permanent magnets: a magnet that will creates and maintains its
own magnetic field over a long period of time.
Examples: Lodestone (a version of Magnetite)-probably
created by lightening striking magnetite
Alloys- magnets created with a combination or alloy
of iron, nickel and cobalt.
Temporary magnets:a magnet that will lose its magnetism.
Example: soft iron
Electromagnet: A magnet can be created by wrapping a wire
around an iron or steel core and running an electrical current
through the wire.
Recall that magnetic fields result from the motion of a
electron.
If you spin a ball of electric charge, the electric charge goes around in a circle.
You effectively have a tiny current going around, and when you have a current
like that you have a magnetic field – the electron becomes a tiny magnet. The
presence of that magnetic effect is pictured as the electric charge spinning
around. If the electron was still, it wouldn’t have this magnetic effect.
Recall:
1. Magnetic flux is the result of the vector
sum of all the individual magnetic fields.
2. Electrons will tend towards the lowest
energy state
3. Paired electrons have the lowest energy
state.
Magnetic properties come about because of the interactions of
unpaired electrons.
Types of Magnetism at an Atomic Level
Diamagnetism
• Diamagnetism is the property of an object or material that
causes it to create a magnetic field in opposition to an externally
applied field.
• It is not the result of unpaired electrons, but is found in all
materials.
• The electrons in a diamagnetic material rearrange their orbits
slightly to create small persistent currents that oppose or repel
the external field.
Diamagnetism (Con't)
• Materials called diamagnetic are those that non-physicists generally
think of as non-magnetic. and include water, wood, most organic
compounds, some plastics and metals with many core electrons such
as mercury, gold and bismuth.
• Superconductor can be considered perfect diamagnet as they expel
all fields.
• In September 2009, NASA announced that they were able to
levitate a mouse using a superconducting magnet
Check here for a brief explanation of how and why you can
levitate a frog using its diamagnetic properties
http://physics.tutorvista.com/electricity-and-magnetism/
diamagnetism.html
Paramagnetism (Temporary Magnet) (con't)
• There will be only a small induced magnetism because only a small
percentage of all of the electron spins (magnetic moments) will
orient with the field.
• Paramagnetic properties are commonly found in transitionals
elements, lanthanides and their compounds as a result of unpaired
electrons in the d and f orbitals.
Paramagnetism (Temporary Magnet)
• Materials in which the unpaired electrons are randomly
arranged.(ie. Aluminum, Manganese, Oxygen gas, Platinum)
• Only becomes magnetic when in the presence of an
externally applied magnetic field.
• Paramagnets will not retain any magnetization in the
absence of the externally applied field because thermal
motion randomizes the electrons spin orientation
Ferromangetism
• Materials in which the unpaired electron spins are all aligned
• These materials have an overall magnetic moment
• A few elements are ferromagnetic at room temperature (iron,
cobalt, nickel)
• The electric energy within these atoms is found to be lower if
the electron spins (magnetic moment) of the valence electrons
are aligned.
• Every ferromagnetic material has its own individual temperature,
called the Curie Temperature or the Curie Point, above which it
loses its ferromagnetic properties. (This is because the thermal
tendency to disorder overwhelms the energy lowering due to
ferromagnetic order.)
Antiferromagnetic
• A material in which the unpaired electrons line up in opposite
directions to one another
• Materials include hematite, chromium, iron Manganese and oxides
such as nickel oxide.
• Antiferromagnetic material have a net magnetic moment of zero
Types of magnetism:
(A) paramagnetism
(B) ferromagnetism
(C) antiferromagnetism
(D) ferrimagnetism
(E) enforced
ferromagnetism.
Credit and ©: SigmaAldrich
http://www.daviddarling.info/encyclopedia/F/ferromagnetism.html
Magnetic Domains and Domain Theory
A magnetic domain is a region within a magnetic material
which has uniform magnetization.
• Magnetic moments (electron spin) in real ferromagnets are not
perfectly aligned.
• They do have perfectly aligned regions within the material, called
magnetic domains
• Each domain has its own magnetization directions.
Magnetic Domains and Domain Theory (con't)
• Domains form as molten material cools into a solid.
• During solidification, a trillion or more atom moments are aligned
• parallel so that the magnetic force within the domain is strong in
• one direction
• Domains tend to be small because this is more energy efficient.
• Ferromagnetic materials become magnetized when the magnetic
domains within the material are aligned.
• This can be done by placing the material in a strong external
magnetic field or by passing electrical current through the
material.
• Some or all of the domains can become aligned. The more
domains that are aligned, the stronger the magnetic field in the
material.
Magnetic Saturation
• When all of the domains are aligned, the material is said to be
magnetically saturated.
• When a material is magnetically saturated, no additional amount
of external magnetization force will cause an increase in its
internal level of magnetization.
The connection between electric current and magnetic field was first
observed when the presence of a current in a wire near a magnetic
compass affected the direction of the compass needle. We now
know that current gives rise to magnetic fields, just as electric
charge gave rise to electric fields.
Magnetic field lines of a permanent magnet, cylindrical coil, iron-core electromagnet, straight
current-carrying wire, and a circular
current-carrying loop.
http://www.physics.sjsu.edu/becker/physics51/mag_field.htm
http://www-istp.gsfc.nasa.gov/Education/Imagnet.html