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Vogel-Fulcher-Tammann freezing of a thermally fluctuating artificial spin ice probed by x-ray photon correlation spectroscopy

DOI: 10.1103/PhysRevB.95.104422 DOI Help

Authors: S. A. Morley (University of Leeds) , D. Alba Venero (ISIS) , J. M. Porro (ISIS) , S. T. Riley (University of Leeds) , A. Stein (Brookhaven National Laboratory) , P. Steadman (Diamond Light Source) , R. L. Stamps (University of Glasgow) , S. Langridge (ISIS) , C. H. Marrows (University of Leeds)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review B , VOL 95

State: Published (Approved)
Published: March 2017
Diamond Proposal Number(s): 10197

Abstract: We report on the crossover from the thermal to the athermal regime of an artificial spin ice formed from a square array of magnetic islands whose lateral size, 30 nm × 70 nm, is small enough that they are dynamic at room temperature. We used resonant magnetic soft x-ray photon correlation spectroscopy as a method to observe the time-time correlations of the fluctuating magnetic configurations of spin ice during cooling, which are found to slow abruptly as a freezing temperature of T 0 = 178 ± 5 K is approached. This slowing is well described by a Vogel-Fulcher-Tammann law, implying that the frozen state is glassy, with the freezing temperature being commensurate with the strength of magnetostatic interaction energies in the array. The activation temperature, T A = 40 ± 10 K, is much less than that expected from a Stoner-Wohlfarth coherent rotation model. Zero-field-cooled/field-cooled magnetometry reveals a freeing up of fluctuations of states within islands above this temperature, caused by variation in the local anisotropy axes at the oxidised edges. This Vogel-Fulcher-Tammann behavior implies that the system enters a glassy state upon freezing, which is unexpected for a system with a well-defined ground state.

Journal Keywords: artificial spin ice, nanomagnetism, frustration, glass, xpcs, coherent

Subject Areas: Physics, Materials, Technique Development

Instruments: I10-Beamline for Advanced Dichroism