A method for extending AC susceptometry to long-timescale magnetic relaxation
A method for extending AC susceptometry to long-timescale magnetic relaxation
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DOI：
10.1039/c9cp03936h
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发表时间：
2019-10-28
影响因子：
3.3
通讯作者：
Rinehart, Jeffrey D.
中科院分区：
文献类型：
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作者：
Hilgar, Jeremy D.;Butts, Aaron K.;Rinehart, Jeffrey D.
随着在分子材料中产生磁各向异性的能力继续达到新的里程碑，协调一致的努力已经转向理解和潜在地控制在大的时间和温度空间内的磁弛豫机制。分子中的慢磁弛豫与温度、磁场和环境高度相关，对于当前的单分子磁体（SMM），相关的时间尺度很容易跨越十个数量级。综合控制磁态的性质（以及磁态之间的跃迁概率）的前景，使得揭示其潜在机制成为一个重要而艰巨的挑战。目前，仪器上的考虑决定了特征弛豫时间τ是根据感兴趣的时间尺度通过单独的方法确定的。静态和动态探测场分别用于长时间尺度和短时间尺度。每种方法都捕获了一个独特的，不重叠的时间范围，实验差异导致了tau作为温度的函数在全球范围内绘制和拟合的根本不同含义的可能性。在这里，我们提出了一种方法来产生长时间尺度的波形与标准的振动样品磁强计（VSM）仪器，允许扩展的交流（AC）磁强计的SMM和其他超顺磁体任意长的弛豫时间。我们适合这些数据的广义德拜模型，并提出了一个比较从直流（DC）磁化衰减得到的结果。
As the ability to generate magnetic anisotropy in molecular materials continues to hit new milestones, concerted effort has shifted towards understanding, and potentially controlling, the mechanisms of magnetic relaxation across a large time and temperature space. Slow magnetic relaxation in molecules is highly temperature-, field-, and environment-dependent with the relevant timescale easily traversing ten orders of magnitude for current single-molecule magnets (SMM). The prospect of synthetic control over the nature of (and transition probabilities between) magnetic states make unraveling the underlying mechanisms an important yet daunting challenge. Currently, instrumental considerations dictate that the characteristic relaxation time, tau, is determined by separate methods depending on the timescale of interest. Static and dynamic probe fields are used for long- and short-timescales, respectively. Each method captures a distinct, non-overlapping time range, and experimental differences lead to the possibility of fundamentally different meanings for tau being plotted and fitted globally as a function of temperature. Herein, we present a method to generate long-timescale waveforms with standard vibrating sample magnetometry (VSM) instrumentation, allowing extension of alternating current (AC) susceptometry to SMMs and other superparamagnets with arbitrarily long relaxation time. We fit these data to a generalized Debye model and present a comparison to results obtained from direct current (DC) magnetization decay.