What happens when a magnet is heated? This is an easy experiment to perform. Above a certain temperature, the magnet loses its ability to attract materials that it would normally attract at room temperature.
Furthermore, iron has a rather strange property: at room temperature, it is attracted to a magnet, but when heated above 770°C, it ceases to be attracted… until it cools and regains this property.
What about an iron magnet? At the same temperature of 770°C, it loses its magnetization, but unlike iron, it does not regain it when it cools. The temperature at which these phase transitions occur between a "magnetizable" state (ferromagnetic) and a "non-magnetizable" state (paramagnetic) is called the Curie temperature. This temperature, known as the critical temperature, depends on the material in question.
The Ising model
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The phenomenon is the same as water freezing. How can a physicist explain it?
The natural approach is to devise a model simple enough to study, yet sophisticated enough to reproduce behavior similar to that of the phenomenon being explained. The physicist must study the model mathematically, guided by an intuitive understanding of the phenomenon. The model is validated by comparing its predictions with the behavior of the physical object. Wilhelm Lenz (1888–1957) discovered the model representing this phenomenon, but it is known as the Ising model, after one of his students, Ernst Ising (1900–1998). In this model, the metal object is represented by a crystal lattice.
