%0 Book Section %1 statphys23_0185 %A Rastelli, E. %A Tassi, A. %A Regina, S. %B Abstract Book of the XXIII IUPAP International Conference on Statistical Physics %C Genova, Italy %D 2007 %E Pietronero, Luciano %E Loreto, Vittorio %E Zapperi, Stefano %K dipole interaction ising model montecarlo simulation statphys23 topic-2 %T Phase diagram of a square Ising model with exchange and dipole interactions %U http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=185 %X The square Ising model with ferromagnetic nearest neighbour (NN) exchange interaction ($J$) and dipole ($g$) interaction is extensively investigated because of its theoretical interest in studying the effect of long range interactions in the critical region and in view of its possible application in describing the qualitative features of the spin configurations observed in ultrathin films of magnetic atoms on metal substrates. Assuming that the spins are aligned perpendicularly to the plane, at increasing $J/g$ the ground state configuration changes from a Néel (N) configuration for $J=0$ to a ferromagnetic (F) configuration for $g=0$ passing through a sequence of $<h>$ striped phases characterized by alternate stripes made up of $h$ rows (columns) of spins up and down. The width of the stripes increases with $J/g$ from $h=1$ to $hınfty$ (F phase). New unexpected irregular checkerboard $<1,n>$ ($<n,1>$) configurations appear between the N and the striped $<1>$ phases. These configurations are characterized by horizontal (vertical) stripes made up of $n$ identical antiferromagnetic rows (columns) followed by $n$ antiferromagnetic rows (columns) of overturned spins. At finite temperature the model is investigated by Monte Carlo (MC) simulation. The study of the specific heat, the order parameter, the probability density distribution of the energy and of the order parameter leads to the conclusion that both first order and continuous phase transitions between the low temperature ordered phase and the high temperature paramagnetic one occur. For values of $J/g$ near the boundary between the striped $<h>$ and $<h+1>$ configurations an intermediate modulated phase occurs between the striped and the paramagnetic phase. The modulated phase is characterized by an order wavevector $Q$ intermediate between the commensurate wavevector characterizing the nearby striped phases $<h>$ and $<h+1>$. This model shows a phase diagram even richer than that found for the well known and widely studied ANNNI model.

@incollection{statphys23_0185, abstract = {The square Ising model with ferromagnetic nearest neighbour (NN) exchange interaction ($J$) and dipole ($g$) interaction is extensively investigated because of its theoretical interest in studying the effect of long range interactions in the critical region and in view of its possible application in describing the qualitative features of the spin configurations observed in ultrathin films of magnetic atoms on metal substrates. Assuming that the spins are aligned perpendicularly to the plane, at increasing $J/g$ the ground state configuration changes from a N\'eel (N) configuration for $J=0$ to a ferromagnetic (F) configuration for $g=0$ passing through a sequence of $<h>$ {\it striped} phases characterized by alternate stripes made up of $h$ rows (columns) of spins up and down. The width of the stripes increases with $J/g$ from $h=1$ to $h\to \infty$ (F phase). New unexpected {\it irregular checkerboard} $<1,n>$ ($<n,1>$) configurations appear between the N and the striped $<1>$ phases. These configurations are characterized by horizontal (vertical) stripes made up of $n$ identical antiferromagnetic rows (columns) followed by $n$ antiferromagnetic rows (columns) of overturned spins. At finite temperature the model is investigated by Monte Carlo (MC) simulation. The study of the specific heat, the order parameter, the probability density distribution of the energy and of the order parameter leads to the conclusion that both first order and continuous phase transitions between the low temperature ordered phase and the high temperature paramagnetic one occur. For values of $J/g$ near the boundary between the striped $<h>$ and $<h+1>$ configurations an intermediate {\it modulated} phase occurs between the striped and the paramagnetic phase. The modulated phase is characterized by an order wavevector $\vec Q$ intermediate between the commensurate wavevector characterizing the nearby striped phases $<h>$ and $<h+1>$. This model shows a phase diagram even richer than that found for the well known and widely studied ANNNI model.}, added-at = {2007-06-20T10:16:09.000+0200}, address = {Genova, Italy}, author = {Rastelli, E. and Tassi, A. and Regina, S.}, biburl = {https://www.bibsonomy.org/bibtex/227cffa581026c29cd590d97efbb9a6e9/statphys23}, booktitle = {Abstract Book of the XXIII IUPAP International Conference on Statistical Physics}, editor = {Pietronero, Luciano and Loreto, Vittorio and Zapperi, Stefano}, interhash = {d03274217498d515eab37542d6ecd412}, intrahash = {27cffa581026c29cd590d97efbb9a6e9}, keywords = {dipole interaction ising model montecarlo simulation statphys23 topic-2}, month = {9-13 July}, timestamp = {2007-06-20T10:16:13.000+0200}, title = {Phase diagram of a square Ising model with exchange and dipole interactions}, url = {http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=185}, year = 2007 }