Abstract
We report on the study of the thermal dynamics of square artificial spin ice, probed by means of temperature- and frequency-dependent ac susceptibility. Pronounced influence of the interisland coupling strength was found on the frequency response of the samples. Through the subsequent analysis of the frequency- and coupling-dependent freezing temperatures, we discuss the phenomenological parameters obtained in the framework of the Vogel-Fulcher-Tammann law in terms of the samples' microscopic features. The high sensitivity and robust signal to noise ratio of ac susceptibility validate the latter as a promising and simple experimental technique for resolving the dynamics and temperature driven dynamics crossovers for the case of artificial spin ice.
Highlights
Artificial spin ice (ASI), i.e., arrays of magnetostatically coupled ferromagnetic islands—mesospins [1]—fabricated by nanolithography [2,3,4,5], exhibit collective phenomena, and, importantly, their interaction strength and geometry can be tailored almost at will [6,7,8,9,10,11]
The shape of the peaks is similar for the three arrays, while a shift in the peak position Tm towards higher temperatures is observed with decreasing interisland distance, i.e., increasing interisland coupling strength
We studied the ac susceptibility of thermally active square ASI arrays of varying interaction strength
Summary
Artificial spin ice (ASI), i.e., arrays of magnetostatically coupled ferromagnetic islands—mesospins [1]—fabricated by nanolithography [2,3,4,5], exhibit collective phenomena, and, importantly, their interaction strength and geometry can be tailored almost at will [6,7,8,9,10,11]. With the exception of early work based on temperature-dependent magneto-optical measurements [12] and more recent works using synchrotronbased magnetic microscopy [6] and muon relaxation [20,21], experimental studies of thermally induced transitions are scarce. To this end, ac susceptibility is a well-established and accessible technique for probing magnetization dynamics, giving access to a wide frequency range [22,23]. Exploring the frequency dependence of the ac susceptibility signal we employ the Vogel-Fulcher-Tammann (VFT) law, that can be used for describing the low-field magnetic relaxation of weakly interacting nanoparticle systems [24,25] but has recently been applied to ASI systems [16,17], attempting to extract parameters that can be directly related to the magnetostatic energies of the ASI arrays.
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