Condensed Matter Theory

Abstract:

We study the classical Heisenberg model for spins on a pyrochlore lattice interacting via long range dipole-dipole forces and nearest neighbor exchange. Antiferromagnetic exchange alone is known not to induce ordering in this system. We analyze low temperature order resulting from the combined interactions, both by using a mean-field approach and by examining the energy cost of fluctuations about an ordered state. We discuss behavior as a function of the ratio of the dipolar and exchange interaction strengths and find two types of ordered phase. We relate our results to the recent experimental work and reproduce and extend the theoretical calculations on the pyrochlore compound, Gd$_2$Ti$_2$O$_7$, by Raju \textit{et al.}, Phys. Rev. B {\bf 59}, 14489 (1999).

Abstract:

Lattice Boltzmann simulations are used to study the phase ordering of a system quenched into a lamellar phase. Hydrodynamic modes are found to be essential for the fluid to avoid frozen metastable configurations and reach the equilibrium state. We also show that a shear imposed on an equilibrium array of droplets can induce a micellar-lamellar transition. ©Société Itoliana di Fisica.