Pressure induced phase transition in AgCrS2 with extreme magnetoelastic coupling

Studying the effect of magnetoelastic coupling is at the heart of materials research for multiferroic applications. Typically, such an effect is small and relies on a modification of the magnitude of exchange interaction by a structural distortion. On the other hand, entirely new physics may be unlocked in the extreme limit where a small structural distortion can change the sign of the exchange coupling. However, such a limit, where one expects both drastically enhanced functionality of a material and new exotic phases and critical behaviour, is experimentally very rare. Remarkably, such an extreme form of magnetoelastic coupling has been demonstrated in the delafossite, AgCrS2, with a Cr-triangular lattice. In this material, inelastic neutron scattering discovered a sign change of the exchange coupling along bonds differing only by ~1% below Tn~42K. We therefore propose to carry out pressure-dependent neutron diffraction measurements at PEARL to study the effect of a lattice compression on the magnetic order in AgCrS2. By applying a ~5GPa pressure, we expect to drive a transition from a ferromagnetic side to an antiferromagnetic side by crossing a regime where the exchange, J, is approximately 0. An unusual regime of J~0, where magnetic fluctuations become fundamentally intertwined with lattice fluctuations, have been rarely explored. Our study is therefore expected to unlock completely new directions in the study of magnetoelastic coupling.