The adsorption of cobalt (Co) and cobalt-boron (CoxB) magnetic nanoparticles (NPs) at a liquid/liquid interface is examined. The Co NPs have a remanent magnetization while the CoxB is completely demagnetized in the absence of an external magnetic field. Cyclic voltammetry experiments reveal that the adsorption of these NPs at the interface shifts the positive potential limit toward lower values showing that a catalytic effect on the ion transfer process is occurring, while electrochemical impedance spectroscopy demonstrates that their mode of self-assembly is directed by their magnetic properties. CoxB NPs form a homogeneous film while Co segregates in macroscopic patches, leaving some areas of the interface uncovered. (C) 2015 Elsevier B.V. All rights reserved.