Answer
The saturation magnetization decreases with increasing temperature for ferromagnetic materials because the atomic thermal vibrational motions counteract the coupling forces between the adjacent atomic dipole moments, which causes some magnetic dipole misalignment.
Ferromagnetic behavior ceases above the Curie temperature because the atomic thermal vibrations are sufficiently violent that they completely destroy the mutual spin coupling forces.
Work Step by Step
The saturation magnetization decreases with increasing temperature for ferromagnetic materials because the atomic thermal vibrational motions counteract the coupling forces between the adjacent atomic dipole moments, which causes some magnetic dipole misalignment.
Ferromagnetic behavior ceases above the Curie temperature because the atomic thermal vibrations are sufficiently violent that they completely destroy the mutual spin coupling forces.