Co纳米片在受限半金属环境中的热激活磁化和电阻衰减
Thermally Activated Magnetization and Resistance Decay during Near Ambient Temperature Aging of Co Nanoflakes in a Confining Semi-metallic Environment
摘要：
我们报告的观察磁性和电阻老化的自组装纳米粒子系统中产生的多层Co/Sb三明治。老化衰减的特点是由一个初始的缓慢衰减，然后是一个更快速的衰减在磁化和电阻。对于沉积在35 $^oC$的样品，衰减很大，几乎占磁化强度的70%和电阻的40%。对于以50 $^oC$沉积的样品，磁化衰减占磁化的$\sim 50%$和电阻的50%。在衰减的更快部分期间，衰减的斜率的斜率改变符号，并且该拐点可以用于提供特征时间。在$35 ^oC$沉积的样品中，特征时间具有强烈的系统性温度依赖性，范围从400 K的$\sim1$ x $10^2 s$到320 K的$\sim3$ x $10^5 s$。对于给定的老化温度，在50 $^oC$下沉积的样品显示出特征时间的7-8倍增加（与$35 ^oC$样品相比），表明该时间尺度可以是可调的。温度标度和时间标度都在潜在有用的范围内。老化前的扫描隧道显微镜（STM）显示Co以纳米级薄片形式形成。在老化过程中，纳米片熔化并以各向异性的方式彼此迁移，形成细长的Co纳米线。这种老化行为发生在封闭的Sb层的封闭环境中。特征时间与老化温度的关系符合阿克里尼乌斯定律，表明活化动力学。
英文摘要：
We report the observation of magnetic and resistive aging in a self assembled nanoparticle system produced in a multilayer Co/Sb sandwich. The aging decays are characterized by an initial slow decay followed by a more rapid decay in both the magnetization and resistance. The decays are large accounting for almost 70% of the magnetization and almost 40% of the resistance for samples deposited at 35 $^oC$. For samples deposited at 50 $^oC$ the magnetization decay accounts for $\sim 50%$ of the magnetization and 50% of the resistance. During the more rapid part of the decay, the concavity of the slope of the decay changes sign and this inflection point can be used to provide a characteristic time. The characteristic time is strongly and systematically temperature dependent, ranging from $\sim1$x$10^2 s$ at 400K to $\sim3$x$10^5 s$ at 320K in samples deposited at $35 ^oC$. Samples deposited at 50 $^oC$ displayed a 7-8 fold increase in the characteristic time (compared to the $35 ^oC$ samples) for a given aging temperature, indicating that this timescale may be tunable. Both the temperature scale and time scales are in potentially useful regimes. Pre-Aging, Scanning Tunneling Microscopy (STM) reveals that the Co forms in nanoscale flakes. During aging the nanoflakes melt and migrate into each other in an anisotropic fashion forming elongated Co nanowires. This aging behavior occurs within a confined environment of the enveloping Sb layers. The relationship between the characteristic time and aging temperature fits an Arrhenius law indicating activated dynamics.
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