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Abstract

The ability to control the light–matter interaction and the simultaneous tuning of both the structural order and disorder in materials, although important in photonics, remain major challenges. In this paper, we demonstrate that path length dictates light–matter interaction for the same crystal structure, formed by the ordering of magnetic nanoparticle self-assembled columns inside magnetic nanofluid under applied field. When the path length is shorter (L = 80 m , m ) the condition for maintaining temporal coherencefor the constructive interference is therefore satisfied, resulting in the formation of a concentric diffraction ring pattern; while for a longer path length (L = 1 mm ,) only a corona ring of scattered light is observed. Analysis of diffraction ring pattern suggests the formation of 3D hexagonal crystal structure, where the longitudinal and lateral inter-column spacings are 5.281 μm and 7.344 μm, respectively. Observation of speckles and diffuse scattering background within the diffraction ring pattern confirms the presence of certain degree of crystal disorder, which can be tuned by controlling the applied field strength, nanoparticle size and particle volume fraction. Our results provide a new approach to develop next generation of tunable photonic devices, e.g. tunable random laser, based on simultaneous harnessing of the properties of disordered photonic glass and 3D photonic crystal.