Vogel-Fulcher-Tammann freezing of a thermally fluctuating artificial spin ice probed by x-ray photon correlation spectroscopy
Vogel-Fulcher-Tammann freezing of a thermally fluctuating artificial spin ice probed by x-ray photon correlation spectroscopy
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DOI：
10.1103/physrevb.95.104422
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发表时间：
2017-03-16
影响因子：
3.7
通讯作者：
Marrows, C. H.
中科院分区：
文献类型：
--
作者：
Morley, S. A.;Venero, D. Alba;Marrows, C. H.
我们报告的交叉从热的非热制度的人工自旋冰形成的一个正方形阵列的磁性岛屿，其横向尺寸，30纳米× 70纳米，是足够小，他们在室温下是动态的。我们使用共振磁软X射线光子相关谱作为一种方法来观察自旋冰在冷却过程中的波动的磁配置的时间-时间相关性，这被发现突然放缓的冻结温度T-0 = 178 +/- 5 K的接近。这种减慢被Vogel-Fulcher-Tammann定律很好地描述，这意味着冻结状态是玻璃状的，冻结温度与阵列中静磁相互作用能的强度相称。的活化温度，TA = 40 +/- 10 K，是远远低于预期的Stoner-Wohlfarth相干旋转模型。零场冷却/场冷却磁强计揭示了释放的状态波动的岛屿内高于此温度，在氧化的边缘的局部各向异性轴的变化所造成的。这种Vogel-Fulcher-Tammann行为意味着该系统在冻结时进入玻璃态，这对于具有明确定义的基态的系统来说是意想不到的。
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.