Control of Surface Segregation in Bimetallic NiCr Nanoalloys Immersed in Ag Matrix

Cr-surface segregation is a main roadblock encumbering many magneto-biomedical applications of bimetallic M-Cr nanoalloys (where M = Fe, Co and Ni). To overcome this problem, we developed Ni(95)Cr(5):Ag nanocomposite as a model system, consisting of non-interacting Ni(95)Cr(5) nanoalloys (5 ± 1 nm) immersed in non-magnetic Ag matrix by controlled simultaneous co-sputtering of Ni(95)Cr(5) and Ag. We employed Curie temperature (T(C)) as an indicator of phase purity check of these nanocomposites, which is estimated to be around the bulk Ni(95)Cr(5) value of 320 K. This confirms prevention of Cr-segregation and also entails effective control of surface oxidation. Compared to Cr-segregated Ni(95)Cr(5) nanoalloy films and nanoclusters, we did not observe any unwanted magnetic effects such as presence Cr-antiferromagnetic transition, large non-saturation, exchange bias behavior (if any) or uncompensated higher T(C) values. These nanocomposites films also lose their unique magnetic properties only at elevated temperatures beyond application requirements (≥800 K), either by showing Ni-type behavior or by a complete conversion into Ni/Cr-oxides in vacuum and air environment, respectively.