The Curie temperature

The spontaneous magnetization due to alignment of the atomic magnetic moments depends on temperature, and it falls precipitously to zero at the Curie temperature T_C. The magnetic ordering is a continuous thermodynamic phase transition with a λ-shaped anomaly in specific heat, associated with disordering of the atomic dipole moments. Above T_C, M_s (T ) is zero; below T_C, Ms (T ) is reversible. This behaviour is illustrated for nickel in Fig. 1.1.
The Curie temperatures of the three ferromagnetic metals, iron, cobalt and nickel, are 10⁴⁴ K, 1388 K and 628 K, respectively. No material is known to have a higher Curie temperature than cobalt. Magnetite has a Curie temperature of 856 K.​

Figure 1.1: Temperature dependence of the spontaneous magnetization of nickel. The Curie point at 628 K is marked.