Dynamics of a fractal set of first-order magnetic phase transitions in frustrated Lu2CoMnO6

The axial next-nearest-neighbor Ising model predicts a fractal (infinite) set of phases with incommensurate wave vectors that are separated by first-order phase boundaries. This complexity results from a simple frustration condition between nearest- and next-nearest-neighbor interactions along a chain of Ising spins. Using x-ray photon correlation spectroscopy (XPCS), we investigate the surprising antiferromagnetic dynamics that emerge from such a complex phase diagram over a wide range of temperatures. We present XPCS measurements of the frustrated magnetic chain compound Lu2CoMnO6 and Monte Carlo simulations. Incommensurate magnetic Bragg peaks slide towards commensurate up-up-down-down spin order with decreasing temperature and increasing time. Both simulation and experiment support a counterintuitive upside-down temperature dependence of the magnetic dynamics: at higher temperatures in the region of first-order phase boundaries, slower dynamics are observed where the speckle maintains its coherence. At the lowest temperatures, where part of the sample adopts commensurate order, the dynamics speed up and result in fast decoherence.

Automated summary

The axial next-nearest-neighbor Ising model predicts a fractal set of phases with incommensurate wave vectors separated by first-order phase boundaries. Using XPCS, researchers investigated antiferromagnetic dynamics in the compound Lu2CoMnO6, observing surprising temperature-dependent changes in magnetic dynamics. Both simulation and experiment support an unexpected temperature dependence where slower dynamics are observed at higher temperatures near phase boundaries, while faster dynamics occur at lower temperatures with commensurate order.