Abstract.
The phenomenon of magnetostriction where a material is deformed by changing the magnetization has been known for almost two centuries. It is caused by interactions between the magnetic moments and the material’s elastic degrees of freedom. Besides deforming a material in the magnetically ordered state, such interactions can also affect the phase transition into the magnetically ordered state as the temperature is lowered. In fact, it has been known for a long time that elastic modes in a ferromagnet can turn a continuous magnetic phase transition into a discontinuous one if the spin-phonon coupling is sufficiently strong.
In certain two-dimensional frustrated magnets there are finite temperature phase transitions that are not associated with magnetic ordering, but rather with a spin-symmetric scalar order that breaks one or more discrete lattice point group symmetries. In this talk I will address how lattice deformations influence such phase transitions. Specifically we study the J1-J2 frustrated classical Heisenberg model on the square lattice where the spins are coupled to two-dimensional lattice deformations modelled as elastic springs. To infer properties of the finite temperature phase transition we calculate the free energy of the system by an approximate self-consistent diagrammatic expansion that we solve numerically. Our results indicate that also this phase transition can be made discontinuous if the spin-phonon coupling is strong enough.
(The slides will be available here)