INSTITUTO DE FISICA DE LIQUIDOS Y SISTEMAS BIOLOGICOS
Unidad Ejecutora - UE
congresos y reuniones científicas
Order by Disorder in an antiferromagnetic Ising pyrochlore
FERREYRA, MARÍA VICTORIA; GURUCIAGA, PAMELA CAROLINA; BORZI, RODOLFO; GRIGERA, SANTIAGO ANDRÉS
Otro; School in Computational Condensed Matter Physics: From Atomistic Simulations to Universal Model Hamiltonians; 2015
The Abdus Salam International Centre for Theoretical Physics (ICTP)
We present a study of an antiferromagnetic Ising pyrochlore by means of computational simulations. The Ising-like spins live on the vertices of a corner-sharing tetrahedra lattice (pyrochlore lattice), pointing in or out of the elementary tetrahedra along the local directions <111>. The spin configuration can be mapped into a simpler system by replacing the magnetic dipoles of the pyrochlore sites (spins) by dumbbells consisting of equal and opposite magnetic charges situated at the vertices of a diamond lattice . In this way, depending on the spin configuration, the diamond lattice can host four types of charge (magnetic monopoles): positive or negative, single or double. In our system, the ground state is a crystal of alternating double monopoles ( all-in/all-out configuration). If the system is placed in a  magnetic field, the lowest energy state has every tetrahedron in a 3in-1out or 3out-1in configuration, i.e., the ground state consists of single monopoles. The field along the  direction couples only two spins per tetrahedron, since the other spins are orthogonal to that direction. The double monopoles are now the lowest excitations. At T=0 the ground state is disordered, but at finite (low) temperature a charge crystalline order appears. This effect is known as order by disorder. We study this phenomena by Monte Carlo simulations, using the Wang-Landau algorithm to approximate the density of state of the system, and the Metropolis algorithm to complete the characterization.