moving charged particle generates a magnetic field
ms= +1/2 --- spins up and aligns with magnetic field
ms= -1/2 ---- spins down and aligns against the magnetic field
occurs when the spins of unpaired electrons in a cluster of atoms in the solid align themselves in the same direction
In the absence of an external magnetic field, the unpaired electrons in the atoms or ions of a substance are randomly oriented. If a magnetic field is imposed, then these spins will tend to become aligned with the field.
Substances in which all electrons are paired (with two electrons of each pair having opposite spins) experience a slight repulsion when subjected to a magnetic field.
no unpaired electrons
Pauli Exclusion Principle
No two electrons in an atom can have the same set of four quantum numbers.