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

Article

关键词: PARTICLE SYSTEM;    DYNAMICS;    GLASSES;    DEPENDENCE;    ENTROPY;    LAW;    TEMPERATURE;    RELAXATION;    VISCOSITY;    DY2TI2O7;   

DOI  :  10.1103/PhysRevB.95.104422

来源: SCIE

【 摘 要 】

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 x 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, TA = 40 +/- 10 K, is much less than that expected from a Stoner-Wohlfarth coherent rotation model. Zerofield- 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.

【 授权许可】

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