Types of Magnetism
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Paramagnetic materials contain unpaired electrons -- atomic or molecular orbitals with precisely one electron. While paired electrons' magnetic moments point in opposite direction, making their magnetic fields cancel out, an unpaired electron is free to align its magnetic moment in any direction. When an external magnetic field is applied, these magnetic moments will normally align themselves in the same direction as the applied field, thus making it stronger.
The tendency of a material to oppose an applied magnetic field and be repelled, is called Diamagnetism, and appears in all materials. However, in a given material with a tendency to enhance an external magnetic field (paramagnetic), the paramagnetic behavior is dominant. Therefore, diamagnetic behavior is observed only in purely diamagnetic material. There are no unpaired electrons, so electron magnetic moments cannot produce bulk effects. In these cases, magnetization comes from the orbital motions of electrons, which are classically understood as:
When a material is placed inside a magnetic field, electrons circling the nucleus experience a Lorentz force from the magnetic field. Depending on the directional orbit of the electron, this Lorentz force may increase the centripetal force on the electrons, pulling them inward toward the nucleus. It may also decrease the force and pull electrons away from the nucleus. This effect increases the orbital magnetic moments that were aligned opposite the field while decreasing the ones aligned parallel to the field. (As per Lenz's Law). The result is a small, bulk magnetic moment with an opposite direction to the applied field.
It's important to note that all materials undergo this orbital response. However, in paramagnetic and ferromagnetic substances, the diamagnetic effect is overwhelmed by the much strong effects the unpaired electrons cause.
Like a paramagnetic substance, a ferromagnet contains unpaired electrons. However, these materials also contain a tendency for their magnetic moments to orient parralle with each other to maintain a lowered-energy state. This state exists along with the tendency for electrons' intrinsic magnetic moments lining up parrallel to an applied field. Thus, even when the applied field is removed, the electrons maintain their parallel orientation.
Every ferromagnetic material maintains its own individual temperature, known as the Curie temperature or Curie point. At this point, the material loses its ferromagnetic properties. The thermal tendency to disorder overwhelms the energy-lowering due to ferromagnetic order.
Well known ferromagnetic materials that easily form magnets are iron, nickel, cobolt, gadolinium, and their associated alloys.
Unlike ferromagnets, antiferromagnets' magnetic moments of neighboring valence electrons point in opposite directions. Antiferromagnets have a magnetic moment of zero, meaning they produce no magnetic field. They are mostly observed at low temperatures and compared to other magnetic behaviors are less common.
Similarily to ferromagnets, ferrimagnets retain
magnetization when a magnetic field is not present. However, their
neighboring electron pairs like to point in opposite directions, like
antiferromagnets. Contrary to initial perception, this does not create
contradictory properties. In an optimal geometrical arrangement, the
electrons that point in one direction create more magnetic moment than those
pointing in the opposite direction.
Electromagnetism occurs when magnetism occurs by applying electric current. When the current is not applies, the item contains no magnetic properties. When current is active, it aquires a strong magnetic pull and magnetic field.
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