Restoration of the continuous phase transition induced by frozen disorder in systems with two interacting order parameters

Abstract

A model which in the thermodynamic limit calculates the partition function exactly is used to study the phase transitions of systems with two interacting order parameters coupled to their respective random fields. An ordered phase is always unstable for the spatial range d ഛ 4 when both random fields are present. A continuous phase transition is possible when only one of the random fields is nonzero. For this case, a diagram of the equilibrium order parameter as a function of temperature for three different strengths of the random field is constructed. The critical temperature decreases with increasing randomness. The slope of the order parameter becomes steeper as the random field decreases and diverges as the randomness vanishes. These results can be contrasted with pure systems of coupled parameters where a fluctuation-induced first-order transition occurs.

Effect of disorder on the thermodynamic phase transition inLa0.70Ca0.30MnO3

“…We believe this suggests the coexistence of both FM and canted-FM regions at low magnetic field, with pure FM predominant at high field. From a theoretical standpoint, 12 the introduction of a random field is not expected to induce first-order behavior. This supports our assertion that Y doping leads to competition between DE and SE interactions, which results in an inhomogeneous FM state in low magnetic fields.…”