Higher-Order Critical Points in Magnetic Systems
Some of the most outstanding successes of the modern theory of critical phenomena have occurred as a consequence of theoretical and experimental studies of so-called higher-order critical or multicritical points. In general, a phase transition occurs when a given thermodynamic parameter (usually temperature) reaches a special or critical value. However, in many cases it is possible to vary a magnetic system’s behavior by varying other accessible thermodynamic parameters (e.g., pressure, stress, or applied electric and magnetic fields). Within the phase diagram generated by this set of parameters, the usual critical point develops into a critical line or surface. While many properties of the system near a critical point are asymptotically independent of its location on the critical surface, there can exist special points on the surface characterized by different critical behavior. The characteristics of these higher-order critical points will be the subject of these lectures. We shall discuss in particular tricritical, bicritical, and Lifshitz points. In view of the program of this school, we shall develop the theoretical models in terms of magnetic systems and materials.
KeywordsAnisotropy Phen Ferro Exter
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