It is the class of physical attributes that are mediated by a magnetic field. The magnetic moments of elementary particles and electric currents give rise to a magnetic field and it acts on other currents and magnetic moments. Ferromagnetic materials are strongly attracted by magnetic fields and can be magnetized to become permanent magnets thereby producing magnetic fields themselves. Among the ferromagnetic substances the most common ones are iron, cobalt,nickel and their alloys. The rare-earth metals such as neodymium and samarium are less common examples. The word ferro- refers to iron, because permanent magnetism was first observed in lodestone. Almost every substance exhibits some type of magnetism. Magnetic materials are classified based on their bulk susceptibility. Paramagnetic substances are weakly attracted to an applied magnetic field. For example, aluminum and oxygen .Diamagnetic substances are weakly repelled. For example copper and carbon. Antiferromagnetic materials have a more complex relationship with a magnetic field. For example chromium and spin glasses. The magnetic state of a material depends on pressure, applied magnetic field and temperature. Though the exact mathematical relationship between strength and distance varies,the strength of a magnetic field almost always decreases with distance.
The tendency of a material to oppose an applied magnetic field, and therefore, to be repelled by a magnetic field is called diamagnetism.The paramagnetic behavior dominates in a material with paramagnetic properties. There are no unpaired electrons in a diamagnetic material hence the intrinsic electron magnetic moments cannot produce any bulk effect. In such cases, the magnetization arises from the electrons’ orbital motions.When a material is put in a magnetic field, the electrons circling the nucleus will experience Coulomb attraction to the nucleus, and a Lorentz force from the magnetic field. This force may increase the centripetal force on the electrons depending on which direction the electron is orbiting thus pulling them in towards the nucleus, or it may decrease the force thus pulling them away from the nucleus. Thus the orbital magnetic moments are aligned opposite the field and decreases the ones aligned parallel to the field.
There are unpaired electrons in a paramagnetic material.That is atomic or molecular orbitals with exactly one electron in them. An unpaired electron is free to align its magnetic moment in any direction. These magnetic moments will tend to align themselves in the same direction as the applied field, when an external magnetic field is applied.
As in the case of a paramagnetic substance, ferromagnet has unpaired electrons. There is a tendency for these magnetic moments to orient parallel to each other to maintain a lowered-energy state in addition to the electrons’ intrinsic magnetic moment’s tendency to be parallel to an applied field. The magnetic moments of the electrons in the material spontaneously line up parallel to one another even in the absence of an applied field. There is an individual temperature, called the Curie temperature, or 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. Common examples include iron, nickel, cobalt, their alloys, and some alloys of rare-earth metals.
Check your knowledge
Magnetism is the force exerted by magnets when they attract or repel each
other. Magnetism is caused by the motion of electric charges. Every substance is
made up of tiny units called atoms.
Magnetic forces are non-contact forces; they pull or push on objects without touching them. Magnets are attracted only to a few magnetic metals, not all matter
Each magnetic field contains energy, also called magnetic energy. She is a constant
in physics. Because a magnetic field is generated by electric currents, magnetic
energy is an energy form of moving charge carriers (electrons).
They are Attractive Property – Magnet attracts ferromagnetic materials like iron,
cobalt, and nickel. Repulsive Properties – Like magnetic poles repel each other and
unlike magnetic poles attract each other. Directive Property – A freely suspended
magnet always points in a north-south direction.