Preparation of metastable CoFeNi alloys with ultra-high magnetic saturation (Bs = 2.4–2.59 T) by reverse pulse electrodeposition

•CoNiFe films with Bs values between 2.4 and 2.59 T were obtained by reverse pulse electrodeposition.•The boost in magnetic saturation was enabled by the entrapment of spin rich, MOH deposits in the films, during reverse oxidation step.•XPS analysis of the films indicated the presence of O, possibly, in the form of NiOH, further supporting the assumption of creating and trapping MOH films during reverse anodic pulse.•The films displayed poor thermal stability beyond room temperature, possibly due to the decomposition of NiOH species into NiO, Ni, and H2O at higher temperature.•XRD analysis of the films indicated the presence of body centered cubic (bcc) phase, with a small average grain size around 12.8 nm.•The metastable nature of the films, preclude it from being considered for hard drive, writer pole application.•However, due to their stability at room temperature, we see an open possibility for these materials with ultra-high magnetic saturation in biomedical applications. The results of reverse pulse electrodeposition of CoFeNi films with ultra-high magnetic saturation, i.e. Bs values between 2.4 and 2.59 T, are presented in this work. Based on valence-bond theory (Hund’s rule) it was assumed that the electronic configuration of MOH obtained by one electron reduction of electroactive intermediate (MOH+ads + e → MOHads) or oxidation of metal (M − e + HOH → MOH + H+) would result with larger number of spins per atom for each of transition metals in MOH-precipitated in CoFeNi deposit- with one more spin than their respective neutral metal in the order: Fe > Co > Ni. The experimental results showed that the increase of Bs value above Slater-Pauling curve was not observed for CoFe alloys, thus FeOH and CoOH compounds were not present in deposit. However, the increase of the Bs values above the Slater-Pauling curve (Bs = 2.4–2.59 T) was observed, for CoFeNi films obtained by reverse pulse electrodeposition. Therefore, NiOH as a stable compound is probably formed in a one-electron oxidation step during anodic pulse oxidation reaction precipitated presumably at the grain boundaries, giving rise to the ultra-high magnetic saturation of CoFeNi films. The effects of experimental conditions on elemental composition, magnetic properties, crystal structure, and thermal stability of CoFeNi films were studied.