Partial oxidation of high entropy alloys: A route toward nanostructured ferromagnets

Abstract The present work proposes a new approach to the development of nanostructured ferromagnetic composites based on progressive oxidation of high entropy alloys. Sequential ‘subtraction’ of the metals with the lowest oxidation energy destabilizes the remaining solid solution and induces phase separation at the nanoscale. By exploring immiscibility routes in the multidimensional phase diagrams, the strategy can be used to promote intimate contact between mixed oxides and metallic solid solutions with desired magnetic properties. To demonstrate the concept, the relation between oxidation energy, phase separation, and magnetic behavior has been investigated across the (CoCrCuFeNi)Ox composition space, for 0.1 ≤ x ≤ 1.3, in materials produced by reactive sputtering. The results point out directions for tuning the composition when aiming for phases with specific magnetic properties arranged in complex microstructures.