Explain the origin of magnetic ordering or ordering field.
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Solution
Origin of magnetic ordering:
The origin of magnetic ordering is the quantum mechanical exchange effect.
The physics behind the exchange effect is the coulombic interactions between the two spins.
It depends on whether the spins form a singlet or a triplet.
The singlet state has a symmetric wave function in real space, whereas the triplet has an anti-symmetric wave function in real space.
Due to this electrons stay out of each other way when they are in a triplet state. As a result of which the coulombic interaction between two electrons is less when they are in a triplet state than they are in a singlet state.
So the interaction energy or exchange interaction depends on the relative orientation of the spins of the electrons.
This interaction of the spins of the electrons is known as exchange interaction which leads to the molecular field.
Hence, the origin of the magnetic ordering or ordering field is the quantum mechanical exchange effect.