Exchange-Bias em nanoestruturas magnéticas usando o modelo de Heisenberg Anisotrópico

Abstract

In the last decades much work in thin magnetic films has been motivated by several interesting properties associated with interfaces involving magnetic materials. The key to the understand these magnetic structures is the knowledge about the basic energies involved. There are three basic energy concepts: exchange, dipolar and anisotropy energies. The first controls the magnetic ordering, the second controls the form of the magnetic structures and the latter controls the preferred orientation. Both are phenomenological descriptions of fundamental correlations and energies associated with the electronic and crystalline structure of the material. One of the most important effects studied is the study about Exchange-Bias (EB) effect, discovered in 1956 . The EB effect occurs due to exchange coupling between ferromagnetic (FM) and antiferromagnetic (AFM) layers. Its signature is a shifted hysteresis loop dislocated from zero field. The shift is attributed to the frozen in global unidirectional anisotropy of the system. Several interesting properties are obtained from hysteresis loop as the remanent magnetization which is a residual magnetization in the material when the aligning field is reduced to zero, the coercive field required for cancelling the residual magnetization and the saturation field which is the field required for forcing all magnetic moments of the sample to point in the direction of the external field. In several models presented in recents works, it is predicted that the exchange bias field depends strongly of the values of Jint , but these values for the exchange bias field is many orders of magnitude larger than the experimental results. In this work we study the magnetic behavior of a FM layer put over the (100) face of an uncompensated AFM substrate both with a BCC structure. To study these effects we performed spin dynamic simulations.