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.
Bibliographical noteFunding Information:
We are grateful to A. Tripathi, B. Pound, and S. Chikara for helpful experimental aid and to C. Batista and W. Selke for valuable discussions. Scientific work began in the LDRD program at LANL and was completed (in particular, the theoretical work) as part of the US DOE, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, Condensed Matter Theory Program. This research utilized beamline 23-ID-1 of NSLS II, a US DOE Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704, as well as the facilities of CINT, an Office of Science User Facility operated for the US DOE Office of Science by LANL, and, finally, the facilities of the NHMFL, funded by the US NSF through Cooperative Grant No. DMR-1157490, the U.S. DOE, and the state of Florida. Sample growth efforts at Yonsei University were supported by the National Research Foundation of Korea, Grant No. NRF-2017R1A5A1014862 (SRC program: vdWMRC center, Grants No. NRF-2018R1C1B6006859 and No. NRF-2019R1A2C2002601).
© 2021 American Physical Society.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics