At temperature zero, the system may only take one global sign, either +1 or -1. At higher temperatures, but below formula_5, the state is still globally magnetized, but clusters of the opposite sign appear. As the temperature increases, these clusters start to contain smaller clusters themselves, in a typical Russian dolls picture. Their typical size, called the correlation length, formula_7 grows with temperature until it diverges at formula_5. This means that the whole system is such a cluster, and there is no global magnetization. Above that temperature, the system is globally disordered, but with ordered clusters within it, whose size is again called "correlation length", but it is now decreasing with temperature. At infinite temperature, it is again zero, with the system fully disordered.