Structural effects on magnetic property of reciprocal opalline structures of iron–nickel alloys prepared with template-assisted electrodeposition

Reciprocal opalline structures, opals and corresponding inverse opals, of iron–nickel alloys (FeNi3) were successfully fabricated with template-assisted electrodeposition processes. The magnetic properties of the structures were studied against the structural features, including shape and characteristic length, of these reciprocal opals. The magnetic FeNi3 opals and corresponding inverse opals were obtained from starting polystyrene opals via a double and single templating procedure, respectively. The structural feature sizes of the opal and corresponding inverse opal were adjusted with the diameter of the starting PS spheres, from 250 to 440 nm. The coercive fields of the inverse opals were found much larger than those of the corresponding opals, attributable to the strong local shape anisotropy and intersections of the thin backbone of the inverse opal. The coercive fields increased with decreasing structural feature size, because of the increase in the densities of domain wall pinning sites and domain vortex sites caused by the feature size reduction. The present work demonstrated the drastic effects of shape and characteristic length on the coercive fields of reciprocal structures.