Dynamics of a fractal set of 1st order phase transitions and comparison to XPCS data in Lu2CoMnO6*

The Axial Next Nearest Neighbor Ising model predicts a fractal (infinite) set of phases with incommensurate wave vectors that are separated by 1st order phase boundaries. This behavior emerges from a simple frustration condition between nearest and next-nearest neighbors along a chain of Ising spins. Here, we probe the dynamics of this scenario using Monte Carlo simulations and compare to X-ray photon correlation spectroscopy (XPCS) measurements in Lu2CoMnO6. We resonantly probe the dynamics of speckle within Mn and Co L3-edge antiferromagnetic Bragg peaks. Bragg peaks of incommensurate order slide towards commensurate `up up down down' spin order with decreasing temperature and increasing time. Analysis of the speckle dynamics supports a counter-intuitive dependence of the dynamics on temperature that is consistent with our simulations.