Domain-wall pinning in the incommensurate phase of sodium nitrite.

Abstract

We study the successive phase transitions and the domain-wall pinning in a model for sodium nitrite crystals. We use the Hubbard-Stratanovich transform to derive the Landau-Ginzburg free-energy functional from a microscopic model. The obtained free energy has a quadratic gradient term, and displays behavior consistent with experiments. In particular there exists a free-energy barrier to the domain-wall motion, leading to the possibility of the pinning of domain walls. This intrinsic pinning is interpreted as the origin of the specific-heat anomaly and the hysteresis observed in recent experiments.