Modelo de Heisenberg com campo aleatório e interação Dzyaloshinskii-Moriya

Abstract

The critical behavior of systems that exhibit magnetism has been the subject of intense research. The Heisenberg model deserves special attention because it is a tool to be used to describe the properties of many magnetic, insulators and anisotropic materials. In addition, it is known that the consideration of anisotropic effects in many spin models can result in the presence of tricritical behavior in the phase diagram and thermodynamic properties. In particular, the Dzyaloshinskii-Moriya (DM) interaction consists of an important type of anisotropy, which since the last decades has attracted a great deal of attention, playing an important role in the description of some classes of insulators, as well as in the study of the phenomena involving spin-glass, among others. The presence of disorder in the models, introduced by random variables governed by a given probability distribution, also usually results in the alteration of the critical behavior in relation to the homogeneous system. Therefore, the interest in the systems in the presence of random field has grown. With such motivation, the spin-1/2 and spin-1 anisotropic Heisenberg models with DM interaction and magnetic random field are studied within the framework of Oguchi’s pair approximation. Although the approach is developed for lattices with general coordination number z the model is discussed in detail for the simple cubic lattice (z = 6). The critical behavior dependent on both the DM parameter and the random field is analyzed. The investigation of phase diagrams reveals the presence of tricritical points and the results are extended to describe the behavior of the thermodynamic properties of the system.