Why does iron lose its ferromagnetism above the Curie point?

Iron loses its ferromagnetism above the Curie point because the thermal energy becomes sufficient to overcome the internal forces that maintain the spontaneous alignment of atomic magnetic moments.12

In ferromagnetic materials like iron, quantum mechanical effects create strong coupling between neighboring atoms, forcing their magnetic moments to align in the same direction. This alignment creates a spontaneous magnetization even in the absence of an external magnetic field. However, this ordered state is constantly resisted by thermal agitation.132

When the temperature reaches the Curie point—approximately 1,043 K (770 °C) for iron—the thermal energy becomes high enough to disrupt these spontaneous arrangements entirely. As a result, the long-range magnetic order vanishes, and the material transitions into a paramagnetic state, where it only exhibits weak magnetic behavior in the presence of an external field. Upon cooling below the Curie point, the internal exchange forces regain dominance, allowing the atoms to spontaneously realign and restore the material's ferromagnetic properties.412