Multifunctional properties of CoNi alloy embedded in the SiO2 host: Role of interparticle interaction

Nanocrystalline CoNi alloy is synthesized using sol–gel technique having average size ∼8.5∼8.5 and ∼12nm. High-resolution transmission electron microscopy confirms absence of any oxide phase at the grain boundary. We observe multifunctionality ascribed to large loop shift after the field-cooling and saturation magnetization (MS) depending on interparticle interaction in CoNi alloy embedded in SiO2 matrix. A large loop shift 1.2 kOe is noticed at 5 K for 10.5% volume fraction (ϕϕ). The loop shift decreases with increasing temperature and vanishes around ∼210K where a maximum is observed in zero-field-cooled magnetization. The loop shift decreases with decreasing ϕϕ and vanishes at ϕ=0.01%ϕ=0.01%. Interestingly, MS increases with decreasing ϕϕ and value at ϕ=0.01%ϕ=0.01% approaches to the calculated value of MS for the bulk counterpart. A model has been proposed with ferromagnetic-core and disordered magnetic-shell structure to interpret the results.

Plot of loop shift (left axis) and saturation magnetization (right axis) with volume fraction (ϕϕ). Inset: loop shift after field-cooling with 50 kOe field and no shift after zero-field-cooling.Figure optionsDownload as PowerPoint slideHighlights
► Strong exchange bias (EB) effect is observed for 10.5% volume fraction.
► EB decreases with decreasing volume fraction (ϕϕ) and vanishes at ϕ=0.01%ϕ=0.01%.
► In contrast, saturation magnetization increases with decreasing volume fraction.
► Saturation magnetization (MS) approaches to bulk value at 0.01% volume fraction.
► Large EB and MS at different ϕϕ are appealing for multifunctional applications.