Magnetic transition in ultrathin Co sandwiched between Au layers in [Au (3.16 nm)/Co (1.5 nm)]_x35/Si(100) multilayers

Abstract

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.

Bonding Analysis of [Au (3.16 nm)/Co (1.5 nm)]x35/Si (100) Multilayer Thin Film

“…The overall results provide local structural information which is very useful in some technological importance as per application point of view. These results also support initial work performed on the sample as reported in our previous study [23].…”

“…For present study, electron beam evaporation (EBE) technique under ultra-high vacuum environment is used to deposit multilayer thin film. In our previous study of this multilayer, we found magnetic phase transition and modification in structural and morphological properties as a function of annealing temperature [23]. On the basis of those results, in the present work, we have investigated the local structural information of the constituent elemental layers by X-ray absorption fine structure spectroscopy.…”

“…1, it is clear that there is no significant change (~ 0.37 eV) in edge width for Au atom of MLS with respect to the pure metal, may be due to its chemical stability. While for Co atom that there is significant change (~ 5.65 eV) compared to corresponding pure metal, which may be attributed to its island type growth in between the interface of multilayer thin film [23].…”

“…To maintain the periodicity of the film, the thickness of Au and Co layers in all bilayers was kept same, i.e. the bilayers were periodically deposited [23].…”