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As temperature is inversely proportional to magnetic susceptibility, when T approaches T C the denominator tends to zero and the magnetic susceptibility approaches infinity allowing magnetism to occur. This is a spontaneous magnetism which is a property of ferromagnetic and ferrimagnetic materials.
where C is a material-specific Curie constant, T is the absolute temperature, and T C is the Curie temperature, both measured in kelvin. The law predicts a singularity in the susceptibility at T = T C. Below this temperature, the ferromagnet has a spontaneous magnetization. The name is given after Pierre Curie and Pierre Weiss.
> is the (volume) magnetic susceptibility, is the magnitude of the resulting magnetization (A/m), is the magnitude of the applied magnetic field (A/m), is absolute temperature , is a material-specific Curie constant (K).
There are two other measures of susceptibility, the molar magnetic susceptibility (χ m) with unit m 3 /mol, and the mass magnetic susceptibility (χ ρ) with unit m 3 /kg that are defined below, where ρ is the density with unit kg/m 3 and M is molar mass with unit kg/mol: =; = =.
These include the ferromagnetic phase transition in materials such as iron, where the magnetization, which is the first derivative of the free energy with respect to the applied magnetic field strength, increases continuously from zero as the temperature is lowered below the Curie temperature. The magnetic susceptibility, the second derivative ...
A number of actinide compounds are ferromagnets at room temperature or exhibit ferromagnetism upon cooling. Pu P is a paramagnet with cubic symmetry at room temperature, but which undergoes a structural transition into a tetragonal state with ferromagnetic order when cooled below its T C = 125 K.
In a paramagnetic system, that is, a system in which the magnetization vanishes without the influence of an external magnetic field, assuming some simplifying assumptions (such as the sample system being ellipsoidal), one can derive a few compact thermodynamic relations. [4]
Only three elements are ferromagnetic at room temperature and pressure: iron, cobalt, and nickel. This is because their Curie temperature , T c , is higher than room temperature ( T c > 298K). Gadolinium has a spontaneous magnetization just below room temperature (293 K) and is sometimes counted as the fourth ferromagnetic element.