The superparamagnetic to ferromagnetic transition in ultrathin Co layers has been investigated by systematic annealing of Co ultrathin layer sandwiched between a pair of Au layer in the [Au (3.16 nm)/Co (1.5 nm)]_x35/Si(100) multilayers. Apart from this magnetic transition, annealing‐induced modifications in morphological and structural properties of this discontinuous island like Co ultrathin layer have also been investigated. The thickness and number of Co and Au layers were so chosen as to make a composition of 20 weight percent (wt%) Co in Au matrix. X‐ray diffraction and reflectivity measurements reveal the formation of a bilayer stack showing Bragg's peaks, which disappear upon annealing beyond 200°C due to mixing of layers. Corresponding SQUID results show a transition from superparamagnetic to ferromagnetic phase beyond 200°C, indicating the clusterization of Co, which is enabled by nonmiscible nature of Co and Au. The results are interpreted in terms of annealing‐dependent mobility of Co and Au atoms resulting in superparamagnetic to ferromagnetic and finally to a non‐magnetic phase.

中文翻译：

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夹在[Au（3.16 nm）/ Co（1.5 nm）] x35 / Si（100）多层Au层之间的超薄Co中的磁跃迁

通过对以[Au（3.16 nm）/ Co（1.5 nm）] _{x 35}夹在一对Au层之间的Co超薄层进行系统退火，研究了超薄Co层中的超顺磁至铁磁转变。/ Si（100）多层。除了这种磁跃迁以外，还研究了退火诱导的这种不连续岛（如Co超薄层）的形态和结构性质的变化。选择Co和Au层的厚度和数量，以使得在Au基体中组成20重量％（wt％）的Co。X射线衍射和反射率测量显示双层堆叠的形成，该堆叠显示布拉格峰，在超过200°C退火时由于层的混合而消失。相应的SQUID结果显示，超过200°C，从超顺磁相到铁磁相的转变，表明Co的聚集，这是由于Co和Au的不可混溶性所致。