ANNNI model

The abbreviation annni model is a model for Axial -Next -Nearest - Neighbor Ising.

It is a variant of the well known in statistical mechanics Ising model. In the model, it is assumed that competing ferromagnetic and antiferromagnetic coupling between, along a selected axis of a crystal lattice, and the next work übernächstbenachbarten spins. It describes in particular complicated spatially modulated, commensurate with the crystal lattice structure or incommensurate magnetic superstructures, and phase transitions between such structures.

Its properties are not only of theoretical interest, but they also allow an interpretation of numerous experiments, the on phase diagrams of magnets, alloys and adsorbates.

The Model 1961 was first time mentioned in the physical literature in a paper by Roger James Elliott, University of Oxford. More detailed analyzes only later, in particular by Per Bak, Michael E. Fisher, Walter Selke and Jacques Villain.